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8625 Industrial Parkway, Angola, NY 14006 Tel: 716-549-4700 Fax: 716-549-4772 sales@birdrf.com www.bird-technologies.com
Installation and Operation Manual for
T-Pass® Transmit Multicouplers
73-90-11 Series
Manual Part Number
7-9100
Warranty
This warranty applies for five years from shipping date.
TX RX Systems Inc. warrants its products to be free from defect in material and workmanship at the time of shipment.
Our obligation under warranty is limited to replacement or repair, at our option, of any such products that shall have
been defective at the time of manufacture. TX RX Systems Inc. reserves the right to replace with merchandise of
equal performance although not identical in every way to that originally sold. TX RX Systems Inc. is not liable for dam-
age caused by lightning or other natural disasters. No product will be accepted for repair or replacement without our
prior written approval. The purchaser must prepay all shipping charges on returned products. TX RX Systems Inc.
shall in no event be liable for consequential damages, installation costs or expense of any nature resulting from the
purchase or use of products, whether or not they are used in accordance with instructions. This warranty is in lieu of all
other warranties, either expressed or implied, including any implied warranty or merchantability of fitness. No representative is authorized to assume for TX RX Systems Inc. any other liability or warranty than set forth above in connection with our products or services.
TERMS AND CONDITIONS OF SALE
PRICES AND TERMS:
Prices are FOB seller’s plant in Angola, NY domestic packaging only, and are subject to change without notice. Federal, State and local sales or excise taxes are not included in prices. When Net 30 terms are applicable, payment is
due within 30 days of invoice date. All orders are subject to a $100.00 net minimum.
QUOTATIONS:
Only written quotations are valid.
ACCEPTANCE OF ORDERS:
Acceptance of orders is valid only when so acknowledged in writing by the seller.
SHIPPING:
Unless otherwise agreed at the time the order is placed, seller reserves the right to make partial shipments for which
payment shall be made in accordance with seller’s stated terms. Shipments are made with transportation charges collect unless otherwise specified by the buyer. Seller’s best judgement will be used in routing, except that buyer’s routing
is used where practicable. The seller is not responsible for selection of most economical or timeliest routing.
CLAIMS:
All claims for damage or loss in transit must be made promptly by the buyer against the carrier. All claims for shortages
must be made within 30 days after date of shipment of material from the seller’s plant.
SPECIFICATION CHANGES OR MODIFICATIONS:
All designs and specifications of seller’s products are subject to change without notice provided the changes or modifications do not affect performance.
RETURN MATERIAL:
Product or material may be returned for credit only after written authorization from the seller, as to which seller shall
have sole discretion. In the event of such authorization, credit given shall not exceed 80 percent of the original purchase. In no case will Seller authorize return of material more than 90 days after shipment from Seller’s plant. Credit
for returned material is issued by the Seller only to the original purchaser.
ORDER CANCELLATION OR ALTERATION:
Cancellation or alteration of acknowledged orders by the buyer will be accepted only on terms that protect the seller
against loss.
NON WARRANTY REPAIRS AND RETURN WORK:
Consult seller’s plant for pricing. Buyer must prepay all transportation charges to seller’s plant. Standard shipping policy set forth above shall apply with respect to return shipment from TX RX Systems Inc. to buyer.
DISCLAIMER
Product part numbering in photographs and drawings is accurate at time of printing. Part number labels on TX RX
products supersede part numbers given within this manual. Information is subject to change without notice.
Bird Technologies Group TX RX Systems Inc.
Symbols Commonly Used
WARNING
ESD Electrostatic Discharge
Hot Surface
Electrical Shock Hazard
Important Information
CAUTION or ATTENTION
High Voltage
Heavy Lifting
Bird Technologies Group TX RX Systems Inc.
NOTE
Manual Part Number 7-9100
Copyright © 2011 TX RX Systems, Inc.
First Printing: March 1993
Version Number Version Date
1 03/05/93
2 05/10/93
3 01/24/94
4 07/08/96
5 10/17/11
Changes to this Manual
We have made every effort to ensure this manual is accurate. If you discover any
errors, or if you have suggestions for improving this manual, please send your
comments to our Angola, New York facility to the attention of the Technical Publications
Department. This manual may be periodically updated. When inquiring about updates to
this manual refer to the manual part number and revision number on the revision page
following the front cover.
Contact Information
Sales Support at 716-217-3113
Customer Service at 716-217-3144
Technical Publications at 716-549-4700 extension 5019
Bird Technologies Group TX RX Systems Inc.
Table of Contents
General Description ........................................................................................... 1
T-Pass Selectivity vs. Cavity Loss....................................................................... 4
Unpacking ............................................................................................................ 4
Installation Overview........................................................................................... 4
Assembly.............................................................................................................. 4
Peg Rack Assembly ............................................................................................ 6
Cavity / Isolator Mounting .................................................................................... 6
Installation ........................................................................................................... 7
Intermodulation Considerations........................................................................... 8
Multicoupler Checkout ......................................................................................... 9
Required Equipment .......................................................................................... 9
Procedure .......................................................................................................... 9
Measurement Accuracy ..................................................................................... 9
Multicoupler Tuning .......................................................................................... 11
Tuning Specifics ................................................................................................ 11
Fine Cavity Tuning............................................................................................. 12
Procedure .......................................................................................................... 12
Coarse Cavity Tuning ........................................................................................ 13
Procedure .......................................................................................................... 13
Retuning System to all new Frequencies .......................................................... 14
Multicoupler Expansion .................................................................................... 14
Typical Expansion Channel Installation ............................................................. 14
Peg Rack Procedure ....................................................................................... 14
Relay Rack Procedure..................................................................................... 15
Setting Cavity Insertion Loss ........................................................................... 15
Cavity Loss Setting Procedure 1 ..................................................................... 17
Required Test Equipment .................................................................................. 17
Procedure for T-Pass Loop ............................................................................... 17
Procedure for BandPass Loop .......................................................................... 19
Cavity Loss Setting Procedure 2 ..................................................................... 20
Required Test Equipment .................................................................................. 20
Procedure for T-Pass Loop ............................................................................... 20
Procedure for BandPass Loop .......................................................................... 21
Maintenance ....................................................................................................... 23
Isolators.............................................................................................................. 23
Table of Contents Manual 7-9100-5 10/17/11
Figures and Tables
Figure 1: Interconnect diagram of typical system ................................................ 1
Figure 2: Typical transmitter noise suppression ................................................... 3
Figure 3: Front view of 21 channel multicoupler ................................................... 5
Figure 4: Mounting rack detail .............................................................................. 6
Figure 5: Typical combiner installation ................................................................. 7
Figure 6: Measuring T-Pass channel performance .............................................. 8
Figure 7: T-Pass cavity fine tuning ..................................................................... 11
Figure 8: T-Pass cavity tuning controls .............................................................. 12
Figure 9: Coarse tuning a T-Pass cavity ............................................................ 13
Figure 10: Expansion channel installation .......................................................... 15
Figure 11: Top view of T-Pass cavity ................................................................. 16
Figure 12: Setting loop adjustment reference..................................................... 17
Figure 13: Setting T-Pass loop using step attenuators....................................... 18
Figure 14: Setting BandPass loop using step attenuators.................................. 19
Figure 15: Setting T-Pass loop insertion loss ..................................................... 21
Figure 16: Setting Bandpass loop insertion loss ................................................ 22
Table 1: Specifications .......................................................................................... 2
Table 2: Typical T-Pass channel insertion loss..................................................... 3
Table 3: Test data sheet ..................................................................................... 10
Table 4: Cavity insertion loss reference loop settings......................................... 16
APPENDIX A
800 MHz Isolators (Compact Style)
General Description .......................................................................................... 24
Installation.......................................................................................................... 25
Verifying Isolator Functionality........................................................................ 25
Recommended Test Equipment ...................................................................... 25
Measuring Reverse Isolation (S12) ................................................................... 25
Measuring Insertion Loss (S21)......................................................................... 25
Figure A1: Verifying Reverse Isolation ...............................................................26
Figure A2: Verifying Insertion Loss .................................................................... 26
Figure A3: Typical Reverse Isolation Waveform ................................................ 27
Figure A4: Typical Insertion Loss Waveform...................................................... 27
Table 1: Specifications ........................................................................................ 24
Table of Contents Manual 7-9100-5 10/17/11
GENERAL DESCRIPTION
S
TX5
TX4
TX3
TX2
TX1
Transmitter Combiner (T-Pass)
Figure 1: Interconnect diagram of a typical Trans-
mit T-Pass Combiner. Typical five channel system
shown as an example.
The 73-90-11-NN Series T-Pass Transmit Combiners are designed to connect up to 21 transmitters
to a common antenna. They use three-port bandpass filters (called T-Pass cavities) and ferrite isolators to provide low channel insertion loss, high
isolation between transmitters, high antenna-totransmitter isolation, high intermodulation suppression, and excellent transmitter noise suppression.
T-Pass transmit combiners are broadband and
easily adaptable to the most difficult duplex system
design requirements.
An interconnect diagram of a typical transmit combiner is s h own in Figure 1. The T-Pass filter
passes one narrow band of frequencies and attenuates all others with increasing attenuation above
and below the pass frequency. The T-Pass filter
has a “dual-port” output loop plate which allows the
filter to be easily connected to other T-Pass filters.
Connections between the filters are made with a
“thru-line” cable that behaves like a low loss 50
Ohm transmission line. The thru-line cables are
individually optimized to their own channel frequency. No compromises are necessary to accommodate other channel frequencies. Each channel
can therefore be anywhere in a very broad frequency range.
An isolator is added at the input to each T-pass
channel to increase channel isolation. The ferrite
isolators will isolate the transmitter from unwanted
signals that enter the system via the antenna. The
transmitter sees an excellent impedance match on
its output, because the isolator absorbs reflected
power that would otherwise enter the transmitters
output stage. This improves the stability, spectral
purity and long-term reliability of the transmitter.
The TX combiners can be expanded one channel
at a time with factory-tuned, easy-to-install expansion channel assemblies. Expansion is usually
accomplished without modifications to the existing
system, and usually amounts to nothing more than
placing a new channel assembly, or several, on top
of the existing system. New channel frequencies
can be above, below, or between existing channel
frequencies.
The number of channels in the combiner is indicated by the last two digits of the model number in
place of the NN designation. All of the information
for both installation and expansion is included in
this manual. The combiner is easy to install and
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 1
Specifications (Note 1) 73-90-11-2C-nn 73-90-11-2D-nn
Frequency Range (Note 2) 806 - 960 MHz
Cavity Type and Diameter 3/4-wave 6.625” (168 mm)
Max Continuous TX Power @ Tx-Tx Separation
150 Watts @ 450 KHz
125 watts @ 250 KHz
Isolator Load Power (Continuous) (Note 3) 5W / 60W 5W / 100W
Minimum TX-TX Separation @ Cavity Loss
450 KHz @ -1.25 dB
250 KHz @ -1.80 dB
Channel Insertion Loss See Table 2.
Typical TX-TX Isolation @ Minimum Separation -80 dB
Typical Antenna-TX Isolation -70 dB
Typical TX Noise Suppression See Figure 2.
Nominal Input Impedance, Ohms 50
Maximum Input Return Loss (VSWR) -20 dB (1.22:1)
Temperature Range -30° to +60° C
Connectors, Input and Antenna N(F)
Mechanical Mounting Peg Rack™ included with system
Mounting Options (Notes 4 and 5)
-MC: 14” H x 19” W rack-mount adaptor plates
-LR: System supplied without Peg-Rack
Maximum Number of Channels Per Rack 15
Dimensions (Note 6)
65.25” H x 24” W x 20.7” D
(1659 x 610 x 526 mm)
Weight, lb. (Kg)
Basic single-channel system:
Expansion channel assembly:
31 (14.0)
12 (5.4)
32 (14.5)
13 (5.9)
Notes:
1.-nn in model number represents number of channels.
2.Consult factory on T-Pass multicouplers for frequencies below 806 MHz or above 960 MHz.
3.Models available with 5W/25W loads. Same specifications as 60W and 100W models, except load power.
4. -MC option reduces maximum number of channels to 12 per pack.
5. -LR systems are tuned and tested on customer frequencies, then disassembled for shipping.
6. rack depth with cavity tuning rods at maximum frequency. Rod travel is approximately 2.2” (56 mm).
Table 1: Specifications.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 2
Tx-to-TX Separation Cavity Loss (dB)
Channel Loss (dB) vs. Number of Channels
2 3 4 5 8 10 12
1 MHz
-1.25
-2.1 -2.3 -2.4 -2.5 -2.8 -3.0 -3.3
500 KHz -2.3 -2.8 -3.0 -3.2 -3.6 -3.9 -4.1
450 KHz -2.4 -2.9 -3.2 -3.4 -3.9 -4.1 -4.3
250 KHz -1.80 -3.1 -3.8 -4.1 -4.4 -4.9 -5.2 -5.5
Table 2: Typical T-Pass Channel Insertion Loss.
Note regarding Table 2: The typical channel losses specified here are for equally spaced channels
only. Channel loss may be higher or lower in multicouplers where separation varies from one channel to
another. Contact TX RX Systems for T-Pass channel loss specifications based on your actual system
frequency plan.
0
-5
Attenuation (dB)
-10
-15
-20
-30
-25
-35
-40
-45
-50
-55
0.01 0.1 1 10
Offset from Fo (MHz)
100
73-90-11-Series Systems
6.625" Diameter 3/4-Wave, Fo = 860 MHz
IL = -1.25 dB
IL = -1.80 dB
Figure 2: Typical Transmitter Noise Suppression.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 3
has been factory tuned in most cases so that no
adjustments are necessary. The specifications for
the 73-90-11-NN family of T-Pass combiners are
listed in Table 1 and the typical T-Pass channel
insertion loss is shown in Table 2. The response
curve shown in Figure 2 shows the typical transmitt e r noise suppression. N oise suppression
depends on the cavity’s loss setting.
T-Pass Selectivity vs. Cavity Loss
As in the case of bandpass cavity filters, T-Pass filter selectivity depends on the coefficient of coupling of the cavity loops at re sona nce. Tighter
coupling decreases inser tion loss and selectivity
while loose coupling increases them.
Although 800 - 1000 MHz T-Pass cavity loops can
be set to approximately -0.8 to -3.0 dB insertion
loss at resonance, TX RX Systems Inc. uses two
standard cavity loss settings, -1.25 and -1.80 dB,
that produce adequate selectivity for the majority of
multicoupler applications in this range. The curves
shown in figure 2 represent the lower selectivity
side of the response curve of a typical 6.625 -inch
diameter, 3/4 -wave 860 MHz T-Pass cavity filter.
Br i dging loss in a progressive thr u line T-Pass
structure varies in the same general manner as
bridging loss in a parallel junction bandpass structure; it decreases as cavity selectivity increases.
An optimal cavity loss setting exists that minimizes
channel loss under a specified frequency plan and
number of channels. See Tech-Aid No. 92002 (lit.
NO. D3001D93) for a complete set of selectivity
and bridging loss curves for T-Pass cavities from
66 to 960 MHz.
parts are accounted for. Any shortages should be
reported to TX RX Systems or its authorized representative.
It is important to visually inspect the system components for any shipping damage as soon as possi ble after ta king deliver y. It is the customers
responsibility to file any necessary damage claims
with the carrier.
The transmit combiner is a very rugged device and
is well packaged for damage-free shipping to any
place in the world. However, a high impact during
shipping can have a detrimental affect. A damaged
shipping container is a sure sign of rough handling.
The most easily damaged parts of the combiner
are the tuning rods. These rods are marked where
they exit from the locking nut with a dab of red varnish or other color/type of paint. If this seal appears
to be broken it may indicate that the system has
been detuned in transit.
INSTALLATION OVERVIEW
Installation of a TX RX transmitter multicoupler
con s ists o f som e or all of the follow i n g ste p s
depending on how completely the unit was assembled at the factory:
1) Determine the exact mounting location for the
multicoupler.
2) Assemble the mounting rack.
3) Install the cavities with isolators then install the
T-Pass Thruline cables and accessories into
the rack.
UNPACKING
Most T-Pass transmitter multicouplers are shipped
4) Connect the transmitters and antenna(s) to the
appropriate connectors of the multicoupler.
fully assembled in a cardboard crate. The cavities
are usually mounted in a suitably sized Peg-Rack
which is a patented design of TX RX Systems, Inc.
Other types of mounting may be supplied for cus-
5) Verify proper operation of each channel by
measuring power output for each individual
channel.
tom tailored systems as specified at the time of
order. In order to reduce shipping costs, some multicouplers are shipped partially assembled. In this
case, customer assembly of the mounting rack and
An unassembled multicoupler will usually be broken down into the following general parts groups:
ASSEMBLY
installation of the cavity channels may be required.
1) Peg rack assembly.
Accessories or other products ordered with the
multicoupler will usually be found either already
2) T-Pass cavities with mounting clamps.
mounted in the rack or packaged separately as circumstances dictate. It is important to check the
packing slip against the contents to make sure all
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 4
3) Isolator & loads on mounting brackets with
mounting clamps.
L2
L3
L5
L7
L9
L11
L13
L15
L17
L19
L21
L4
L6
L8
L10
L12
L14
L16
L18
L20
TX 1
TX 2
TX 3
TX 6
TX 7
TX 10
TX 11
TX 14
TX 15
TX 18
TX 19
TX 4
TX 5
TX 8
TX 9
TX 12
TX 13
TX 16
TX 17
TX 20
TX 21
21 Cavity Peg-Rack
Model 93-00-10
Figure 3: Front view of 21 channel multicoupler showing cavity and cable layout. Mul-
ticouplers with fewer channels follow the same cavity stacking and cable pattern from
the bottom up.
Isolator mounting clamp
connecto r positi one d on
bo ttom of c avity for th is
channel only.
Isolator mount i n g cla m p
connec tor access hole on
bottom for this bracket. Hole
is on top for all other isolators.
Tra nsm i t te r s c o nne c t t o
type N connector on isolator.
Channel Number
First cavity has built-in short
circuit.
Antenna connects here
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 5
4) T-Pass thruline cables and isolator to cavity
Figure 4: T-Pass cavity mounting rack detail.
cables.
Peg-Rack Assembly
If the unit was fully assembled then this step may
be disregarded. A separate instruction sheet for
the rack assembly is included with the rack.
Cavity / Isolator Mounting
After the Peg-Rack is assembled, the cavity filters
are mounted. They are packaged separately from
the isolator assemblies. The cavities have an identification tag attached indicating their frequency
which is used to identify the cavity position in the
sy stem. A T-Pass THRULINE DATA SH E ET is
also included in the envelope with this manual for
your multicoupler or expansion channel. This computer printout shows the position of each channel
in the multicoupler and indicates its frequency. This
information determines the position of the cavities
in the rack. This data sheet also shows the position
of critical-length Thruline cables.
The front view of a fully assembled 21 channel TPass transmit combiner is shown in Figure 3. The
location and assembly order are the same for any
size multicoupler.
these cavities will also lay in the peg indentations closest to the vertical rails. The isolator
mounting clamp connectors and access hole
should be on top for these channels.
4) Similarly mount the cavity and isolator assemblies for the channels on the left side of the rack
starting with channel 1 and working up. The
stainless steel clamps that hold the cavities
(part # 8-6212) on the left side should lay in the
peg indentations closest to the center of the
rack. Isolator clamps and access holes are on
top for these channels also.
5) Connect the isolator to the T-Pass cavity as
shown in figure 4, using isolator cable part #31918 for each channel. Use pliers with rubber
jaws (Utica Part #529-10) to tighten the connectors slightly more than finger tight. DO NOT
OVER TIGHTEN.
1) Mount the cavities for channel 2 (TX 2) on the
right side of the rack starting with pegs 2 and 3.
The stainless steel clamps that hold the cavities
(part # 8-6212) on the right side should lay in
the peg indentations closest to the vertical rails.
(Note that the 8-6212 clamps are also used for
mounting the isolator assemblies.) The clamp
always goes around 2 pegs. Orient the cavity as
shown in Figure 4.
2) Identify the isolator assembly for channel 2. The
isolators are labeled with the TX/Channel number and channel frequency. Mount the isolator
assembly to the previously mounted cavity
using two stainless steel clamps. See figures 3
and 4. The clamp connectors for the channel 2
isolator assembly should lie on the underside of
the cavity. An access hole is provided in the isolator mounting plate edge to allow access to
one of the hard to get at clamp connectors. It
should face downward.
3) Mount each remaining cavity and isolator
assembly for the right side (channels 3,6,7 etc.)
following the order shown on the T-Pass
thruline data sheet. The mounting clamps for
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 6
6) Similarly connect the T-Pass Thruline cables to
Radio
Cabinet
Radio
Cabinet
Radio
Cabinet
Radio
Cabinet
Work
Area
T-Pass
Transmitter
Combiner
Figure 5: The multicoupler should be positioned so that there is access for tuning and servicing.
the cavities using the THRULINE DATA Sheet
and figure 3 as a guide.
Four, 17/64" (6mm) diameter mounting holes are
provided in the base for attaching the rack to the
floor using bolts or lag screws.
Caution: The Thruline cables must
be installed in the correct location for
proper operation. Use pliers with rubber jaws to tighten these connections
slightly more than finger tight.
This completes the assembly of the basic multicouplers. Any accessories should be mounted to the
rack using the supplied mounting hardware and
adapter plates.
Installation
The multicoupler should be located in a dry and
level area, indoors. It is best if all transmitters are
as equal in distance as possible from the combiners so that cable losses are the same for all channels. Figure 5 shows a suggested orientation for
the equipment. Two points are important. First, a
work area space should be left as illustrated so that
the tuning controls are easy to access. This will
facilitate tuning when chann el frequencies are
changed. Secondly, space is needed when adding
expansion channels. If there is a lack of space to
access the side of the combiner, then plan to allow
the rack to be moved into the indicated work area
to facilitate adding channels. This will require some
slack in the cables that connect to the station transmitters.
Each transmitter connects to its respective channel
through an ‘N-style’ female connector on the isolator. We recommend using a high quality double
shield or semi-flexible cable for this purpose. Rigid
cable may be used but extreme care is needed to
prevent damage to the connector on the multicoupler. High quality connectors should be used for all
connections to the multicoupler. Connectors with
gold plated center pins are preferred to minimize
the generation of intermodulation distortion products.
The antenna connection is made to a female N
connector on the last T-Pass cavity in the chain
near the top of the rack. A flexible jumper of high
quality coax is convenient for this purpose. This
jumper should be rated to handle the total power
output of all the transmitters combined. Since most
transmitter multicouplers exhibit an average 3 dB
loss, the actual total power output will be approximately 1/2 the total transmitter power. However,
we recommend cable rated at twice the ac tual
required power as a safety factor.
Direct connection to the hard line antenna cable is
also possible but care should be exercised to prevent damage to the cavity connector due to excessive bending force created by misalignment of the
hard line.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 7
It is advised that the center pin on all mating N
UG27 Elbow Connector
& UG57 Male-Male
Adaptor
UG57
Male-Male
Transmitter
Transmitter
Transmitter
Single
or Dual
Section
Isolators
Single
or Dual
Section
Isolators
Single
or Dual
Section
Isolators
T-Pass
Cavity Filter
Channel 3
Channel 2
Channel 1
Wattmeter 2
50 Ohm
Load
Wattmeter 1
This T-Pass Loop
requires a 3-1268
short circuit
connector
Figure 6: Equipment hookup for measuring T-Pass channel performance.
male connectors be checked for proper alignment
before connection to the multicoupler. A cocked
center pin in the male connector can permanently
damage the mating female connector. In many
cases, simple field replacement of the damaged
connector is not possible and replacement of an
entire subassembly may be required to make the
unit operational.
This system is de signed for use with separate
transmit and receive antennas. For best operation,
the transmit and receive antennas should be separated vertically by 20 feet with little or no horizontal
offset between antennas. Lesser separations can
be used but with an increased risk of harmful interference between radio systems. In most cases, it
will be desirable to mount the receive antenna
higher than the transmit antenna to maximize the
talk-back range of low power portable radios.
Intermodulation Considerations
Following the previously mentioned antenna spacing recommendations will go a long way toward
minimizing or eli mina ting inter m odulation (IM)
interference. IM is the result of a frequency mixing
process that occurs when two or more RF signals
are present simultaneously in the same circuitry
where nonlinearity occurs. Product frequencies
generated have frequencies that are determined by
relatively simple mathematical relationships such
as F(im) = 2F1-F2 and are normally determined by
doing a computer intermodulation analysis for the
antenna site. These products can be generated in
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 8
a corroded tower joint, metal-roofing, transmitter
final amplifier or the receiver front-end.
Both cavity filters and ferrite isolators isolate the
transmitters connected to the combiner from oneanother thus reducing intermodulation interference.
However in all transmitter combiners, intermodulation products are reduced in strength but never
completely eliminated. They have to be reduced by
an amount to meet the Federal Communications
Commission, 43 + 10 Log(Power Out) rule for spurious output reduction. Because of the limitations
imposed by the tension and friction joints in connectors, IM products will be down 100 to 120 dB
below carrier so they are still strong enough to
cause problems if they fall on a near-by receiver
frequency.
To avoid transmitter generated IM problems, do
not put two channels on the same combiner that
your IM software predicts will cause interference by
generating either 3rd or 5th order IM products.
Having at least two transmitter combiners allows
maximum flexibility in dealing with transmitter generated IM.
Multicoupler Checkout
Fully assembled multicouplers are factory tuned
and ready for routine operation after properly connecting the transmitters and antenna(s) as outlined
previously. The components used in systems that
require partial assembly have been fully intercabled and tuned so they will not require tuning. However, it is recommended that the performance of
the multicouple r be checked ini tially a nd data
recorded for future reference. This is done by measuring the input and output power of each channel
and recording the data. Figure 6 shows the equipment hook up.
REQUIRED EQUIPMENT
If a power monitoring system is not installed along
with the multicoupler, two Bird Model 43 thruline
wattmeters or equivalent can be used. They should
be equipped with elements for the frequency band
of interest and rated for the expected transmitter
power output. The use of two wattmeters eliminates errors that can occur from changing cable
lengths. The measurements should only be done
one channel at a time because most wattmeters
cannot accurately measure the total power of two
or more transmitters simultaneously. A pocket calculator with Log functions makes for easy calculation of power loss in dB using this measured data.
PROCEDURE
Start with channel 1 at the bottom of the rack and
proceed to the next higher channels. The two wattmeters should be connected to the equipment as
shown in figure 6. Note that the use of the elbow
and/or male-male connectors allows the shortest
connections and negligible hook up loss. Longer
cable lengths will tend to increase measurement
error.
It is important that the same wattmeters and wattme ter elements b e used in the same position
throughout the tests. The serial numbers of the
wattmeters should be recorded for future reference. Wattmeter elements may not have serial
numbers so they need to be labeled or otherwise
keyed to a specific wattmeter to assure repeatability of the measurements.
A convenient data sheet is included in Table 3 and
may be photo copied. After entering the data and
calculating the power losses, it should be retained
for future reference. A column is provided for entering the factory measured loss from the T-Pass
Thruline Data sheet that was included in the envelope w ith this manual . The fa ctor y d a t a was
obtained with a laboratory network analyzer having
an accuracy ±0.05dB. The readings obtained using
the wattmeter method outlined may vary considerably from the factory values and this difference is
explained in the next paragraph.
MEASUREMENT ACCURACY
The Bird thruline wattmeter has a measurement
accuracy of +/- 5% of full scale. When using a 100
watt element in this meter, the measurement error
can be as great as + or - 5 watts.
As an example of the actual dB loss readings that
might be produced using the wattmeter method,
consider a T-Pass channel that has a factory measured loss of 3.0 dB. We would expect that a 100
watt transmitter would produce 50 watts out of this
channel but the actual wattmeter reading for the
input power could measure as low as 95 watts to
as high as 105 watts. The measured output power
could run from 45 to 55 watts. It is possible that the
output reading may be 5 watts low while the input
reading is 5 watts high or just the opposite. These
two extremes would yield the following dB loss values:
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 9
For a Power Out (PO) of 45 watts and a Power
Transmitter Combiner Test Data Sheet
Combiner Model Number:
Serial / Job Number:
Date: Technician:
Wattmeter #1 Serial Number:
Wattmeter #2 Serial Number:
Channel
Number
Power Input
(Pi) in Watts
Power Output
(Po) in Watts
Power Ratio
Po / Pi
Calculated
Loss (dB)
Factory Measured
Loss (dB)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
Table 3: Test Data Sheet.
Input (PI) of 105 watts:
Loss (dB) = 10 Log10 (45/105)
Loss (dB) = -3.7
For a PO of 55 watts and PI of 95 watts:
Loss (dB) = 10 Log10(55/95)
Loss (dB) = -2.4
So the calculated loss for this channel can run from
-2.4 to -3.7dB and be acceptable considering the
measurement error factor. The actual error could
be much greater if a 250 watt element was used;
the measured values could vary by as much as +/-
12.5 watts. So using a wattmeter element with the
smallest possible rating is important for accuracy.
Use of between series adapters or UHF type connectors for making connections to the wattmeters,
device under test or loads, could make this error
even worse due to the additional impedance mismatch that these connectors can cause.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 10
MULTICOUPLER TUNING
Transmitter
Output
Section
Termination
Two Single Section
or One Dual Isolators
T-Pass
Cavity Filter
Wattmeter
To Other
Channels
To Other
Channels
Input
50 Ohm
Termination
Fine
Tuning
Output
Coarse
Tuning
Figure 7: Using a Wattmeter for T-Pass cavity fine tuning.
T-Pass transmitter combiners are pre-tuned at the
factory and usually require no adjustment. T-Pass
expansion channels are also pretuned but may
require fine tuning after being installed in an existing system. Channels that are close in frequency
(adjace nt chann els in the multicoupler) to the
expansion channel may also benefit from fine tuning due to the slight interaction that occurs with the
new channel. The procedures that follow may be
used at any time to verify that any or all channels
are properly tuned or to correct any misalignments.
It is interesting to note that T-Pass filters, bandpass
filters and cavity filters in general can act as impedance transformers as well as filters. It is for this
reason that many field service personnel claim that
they can always tune a filter better than the factory.
What isn't generally realized is that their tuning
efforts are usually producing better impedance
matching between transmitter and antenna which
can be improved by the transforming action of filters. Since the filters are usually tuned using laboratory grade 50 ohm loads, the tuning adjustment
that produces this improved match will be slightly
different than the factory adjustment. While this
tuning may produce slightly greater power output
readings, it will rarely produce any discernible
change in system performance.
It is our recommendation that channel tuning only
be attempted under the previously mentioned conditions or when it is suspected that the combiner
has been tampered with or subjected to extreme
shock in shipping or installation. This condition is
indicated when the channel loss is in excess of that
expected from actual measurement of power input
and output.
Tuning Specifics
Tuning the multicoupler consists of tuning the individual T-Pass channels. T-Pass channel tuning
involves cavity filter tuning. For multicoupler models used at 800 MHz and above, isolator tuning is
never required because these isolators are fixedtuned at the factory for specific frequency bands
and have no user adjustments.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 11
Fine Cavity Tuning
NOTE
Cavity Resonator
Coarse Tuning Rod
Coarse Tuning Lock
10-32 Cap Screw
Calibration Index
Input/Output Port
Loop Plate Assembly
Loop Plate
Hold Down Screws
Loop Plate Assembly
Input/Output Port
Calibration Mark
Calibration Index
Fine Tuning Rod
Fine Tuning Lock
Knurled Thumb Nut
Figure 8: T-Pass cavity tuning controls.
Figure 7 shows a hookup suitable for fine tuning
any channel under power while installed in the multicoupler. The term fine tuning here refers to cavities that have already been tuned to frequency and
may only require adjustment of the fine tuning control (+/- 50 KHz). The transmitter is used as a signal source and the cavity is adjusted for minimum
reflected power.
Procedure
With the transmitter keyed, the cavity fine tuning
control is adjusted (pushed in or out) to obtain a
minimum meter reading. See Figure 8 for a detail
of the cavity tuning controls. If a minimum meter
reading is obtained with the fine tuning rod fully in
or completely out, do the following:
1) Set the fine tuning rod so that about 1/2 its
length is inserted into the cavity.
When tuning a cavity that has been in
service for some time it is not unusual
to find the main tuning rod hard to
move in or out. This occurs because
TX RX uses techniques borr owed
from microwave technology to provide large area
contact surfaces on our tuning plungers. These silver plated surfaces actually form a pressure weld
that maintains excellent conductivity. This pressure
weld develops over time and must be broken to
move the main tuning rod. This is easily accom-
plished by gently tapping the tuning rod with a plastic screwdriver handle or small hammer so that it
moves into the cavity. The weld will be broken with
no damage to the cavity.
When adjusting the coarse tuning rod, it is easy to
put the cavity far off resonance and cause most of
the transmitter power to be reflected back into the
isolator output section load. This load should be
capable of dissipating this power or damage could
result. If in doubt about the loads capability, follow
the coarse tuning procedure outlined below. It is
based on the use of a spectrum analyzer and frequency generator which avoids the need to consider power levels.
2) Loosen the coarse tuning rod locking screw (5/
32"/4mm Allen/HexKey wrench required) and
move the rod in or out slightly to obtain minimum meter reading. Small movements of the
coarse tuning rod are facilitated by tapping the
rod with the handle end of a screw driver while
gently pushing or pulling the main tuning rod.
Tighten the coarse tuning locking screw.
3) Adjust the fine tuning control for a minimum
meter reading.
4) Tighten the fine tuning locking mechanism.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 12
LOAD
Spectrum Analyzer
Bird SignalHawk
Signal Generator
RLB - 150 Bridge
50 Ohm Load
T-Pass
Cavity Filter
3-1268
Short Circuit
Connector
Figure 9: Equipment hookup for
T-Pass cavity coarse tuning.
Coarse Cavity Tuning
Wh e n a T-Pa s s c a vi ty f re q u e nc y ha s t o be
changed by over 50 KHz, adjustment of the main
tuning rod is required. Large frequency changes
are more easily observed when using a tracking
generator and a return loss bridge to give a swept
display of the return loss cur ve. The return loss
curve is a very precise indicator of T-Pass cavity
tuning. The test equipment hookup for doing this is
illustrated in Figure 9 and uses the following equipment;
1) Spectrum Analyzer that covers the frequencies
of interest such as the Bird Technologies “Signal Hawk ™”.
2) Signal generator capable of producing the frequencies of interest.
3) Eagle Return Loss Bridge (35 dB directivity).
Model RLB150N3A.
4) Double shielded coaxial cable test leads
(RG142 B\U or RG223/U).
5) 50 Ohm load with at least -35 dB return loss
(1.10:1 VSWR).
6) Shorting stub from holder at top of T-Pass rack
(Part # 3-1268).
Procedure
1) Set the spectrum analyzer for the desired channel frequency (display center) and vertical scale
of 10 dB/div. Set the signal generator for the
desired center frequency.
2) Connect the return loss bridge to spectrum analyzer and signal generator as shown in figure 9
but do not connect it to the cavity. Leave the
test port (called the load port) on the bridge
open.
3) Set up the 0 dB return loss reference display
on the spectrum analyzer. Then connect the
return loss bridge.
4) Loosen the fine tuning rod locking nut and set
the fine tuning rod so that 1/2 its length is
inserted into the cavity.
5) Loosen the main tuning locking screw and
move the main tuning rod in or out to obtain
maximum return loss at the desired frequency.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 13
Small movements of the main tuning rod are
facilitated by tapping the rod with the handle
end of a screw driver while gently pushing or
pulling the main tuning rod.
6) Lock the Main and Fine tuning rods and reinstall
the cavity in the system. Use the previously outlined fine tuning procedure to verify proper tuning under power.
Retuning System To All New Frequencies
When retuning the combiner to all new frequencies
perform the following procedure in a step-by-step
fashion;
ity. A new thruline cable will connect this channel
to the existing cavities.
The system engineer may also advise that the cavity insertion loss on some of the existing channels
needs to be changed in order to accommodate a
new channel. This can be necessary when the new
channel is much closer in frequency separation to
existing channels than that previously encountered. This usually means increasing the cavity
loss for all close spaced channels which provides
the increased selectivity required. Cavity insertion
loss values are shown on the T-Pass Th r uline
cable sheet.
1) Determine new thruline cable lengths for the
new channels and the specific stacking order in
the rack. TX RX Systems Sales engineers will
assist by making the calculations using their
design software. Due to variations in coaxial
cable characteristics and assembly techniques,
factory supplied cables are recommended.
2) Use the Coarse Tuning procedure as outlined
earlier in this manual to tune each cavity channel to the new transmitter frequencies.
3) Connect the channels according to the new
Thru-line cable chart.
4) Fine tune each channel using the fine tuning
procedure as outlined earlier in this manual,
starting with channel 1 and proceeding to the
next higher channel. After tuning all channels,
repeat this step a second time to verify that
there is no more channel interaction.
5) Verify channel losses if desired using the multicoupler checkout procedure outlined previously.
MULTICOUPLER EXPANSION
Expansion channels for your multicoupler may be
ordered directly from TX RX Systems or its authorized representative. The systems engineer will
help you select the right model and any required
options.
The expansion channel and options are shipped
wi t h mountin g instructions and a n ew T-Pass
Thruline cable sheet which shows the exact mounting location of the new channel in the existing system. In most cases, this channel will be added
directly to the next topmost position in the rack and
the antenna connection will then move to this cav-
Typical Expansion Channel Installation
The following text is a procedure for adding expansio n channe l components to a t y p ical T-Pass
Transmitter Multicoupler. Please keep in mind that
instructions shipped with the expansion components supersede these procedures.
Typical Parts Included
(Quantity and Description)
(1) T-Pass Cavity Assembly.
(1) Single/Dual Isolator w/load on Mounting Plate
(1) 9.4" Isolator to Cavity Interconnect Cable
(4) Stainless Steel Band Clamps
(1) T-pass Thru-line Cable
(1) T-pass Thruline Chart.
PEG RACK PROCEDURE
1) Determine the location of the Expansion Channel in the rack by consulting the new
THRULINE cable chart.
2) Mount the cavity in the peg rack using two (2)
stainless band clamps, refer to Figure 10.
3) Rotate the cavity body so that the connectors
are orientated the same as those on the other
cavities and that no cavity-end cap screws are
preventing a flush fit with a mounting peg.
4) Tighten the cavity mounting clamps.
5) Attach the isolator mounting plate to the cavity
using two (2) band clamps. Clamp screws
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 14
should be positioned as shown in figure 10. Do
NOTE
NOTE
NOTE
Figure 10: Expansion channel installation.
not tighten the clamps.
6) Rotate the isolator mounting bracket so that the
isolator is in the vertical plane as illustrated,
forming a smooth line in relation to the other
channels in the rack.
7) Due to the limited space, tightening may require
the use of a 5/16" open end wrench. Tighten
both clamps securely.
8) Connect the isolator-to-cavity cable. Use a pair
of cable pliers to tighten-up the connectors.
RELAY RACK PROCEDURE
Because of their width, 6.625” cavities
are mounted on relay racks in a horizontal or i e ntati o n o n ca v i ty d eck
plates.
1) Determine the location of the expansion channel in the rack by consulting the new
THRULINE cable chart.
2) If necessary install an empty cavity deck in the
rack using 4 Phillips screws. If there is room on
an already existing cavity deck then skip this
step of the procedure.
9) Connect the new channel to the multicoupler
using the proper length T-Pass Thruline cable.
Use a cable pliers to tighten these connections.
The required length thruline cable and
new cabling chart has either been factory supplied or is to be determined
and fabricated by the customer as
determined at the time of order. Use
T-Pass T H RU L I N E de s i g n she e t s
supplied by the factory.
10) If necessary, reset cavity insertion loss of adja-
cent channels as noted on the Thru-line cable
sheet. Follow the procedure outlined under
Setting Cavity Insertion Loss.
11) Fine tune the T-Pass cavity of the expansion
channel according to the procedure outlined
earlier.
3) Mount the cavity on the deck by laying the cavity onto the “V” shaped cavity bracket.
4) Rotate the cavity body so that the connectors
are oriented the same as those on the other
cavities in the system. Secure the new cavity to
the brackets using (2) stainless band clamps.
5) Tighten the cavity mounting band clamps.
6) Connect the black isolator-to-cavity cable using
a pair of cable pliers to tighten-up the connectors.
7) Connect the new channel to the combiner using
the proper length T-Pass Thruline cable. Use a
pair of cable pliers to tighten these connections.
The required length Thruline cable
and new cabling chart has either been
factory s upplied or i s to be determined and fabricated by the customer
as determined at the time of order.
Use T-Pass Thruline design sheets
supplied by the factory.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 15
8) If necessary, reset the cavity insertion loss of
the adjacent cavities as noted in the Thruline
cable sheet. Follow the procedure outlined
below under Setting Cavity Insertion Loss,
9) Fine tune the T-Pass cavity of the expansion
channel according to the fine tuning procedure
outlined earlier.
SETTING CAVITY INSERTION LOSS
It is sometimes necessary to reset the insertion
loss of a T-Pass cavity filter in order to change its
selectivity. Increasing the loss will increase the
cavity se lectivi t y which m ay be necessary t o
Calibration
Mark
Bandpass
Loop
T-Pass
Loop
Loop Locking
Screws (6 places)
Figure 11: Top view of T-Pass cavity.
Cavity Loss (dB)
Built-in Short
Circuit
Coupling Loop Type
TX RX Systems
Part Number
Reference Notch
Depth (dB)
1.25 No
T-Pass
Bandpass
3-3721
3-2294
-9
-17
1.25 Yes
T-Pass
Bandpass
3-2292
3-2294
-9.6
-16.7
1.80 No
T-Pass
Bandpass
3-3721
3-2294
-6.6
-14.6
1.80 Yes
T-Pass
Bandpass
3-2292
3-2294
-7.2
-13.9
Table 4: Cavity insertion loss reference loop settings.
accommodate more closely spaced channels.
Changing the loss is accomplished by rotating the
coupling loops to change the coefficient of coupling. Both loops are normally adjusted for a given
insertion loss setting. Most T-Pass cavities have a
Calibration Index label beside both loops that gives
a relative indication of their settings (see Figure
11). In actual practice, these marks are not accurate enough for setting loss values consistently.
Two procedures are offered for setting the cavity
loss. Both procedures take advantage of the fact
that when a tee connector is placed on a single
bandpass or T-Pass loop, a rejection notch can be
observed across the tee. The depth of the rejection
notch is directly related to the loop's coefficient of
coupling.
The first procedure uses precision rotary attenuators, a signal generator and an RF millivolt meter to
provide very accurate results. The actual loss setting obtained when this procedure is carefully followed will be within one tenth of a dB of the desired
value and the return loss will be 20 dB (1.25:1) or
better.
The second procedure uses a spectrum analyzer
and frequency generator and produces slightly less
accurate results. When this procedure is carefully
followed, the loss settings will be within two tenths
of a dB of the desired value and the return loss will
usually be -15 dB (1.5:1 VSWR) or better. The
advantage of this procedure is that it is much faster
to do, does not require precision attenuators and
will yield acceptable results in most cases.
Table 4 shows a reference chart for setting T-Pass
cavity loss with either procedure. The chart shows
the desired cavity loss settings and the reference
setting for both the T-Pass and bandpas s loo p
assembly. The reference notch depth for a given
loss is that which can be observed across a tee
connector connected to either loop assembly. Note
that the reference notch depths are slightly different when the T-Pass loop assembly has a built-in
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 16
short circuit. This loop is only used once in the bot-
ZERO
SET
ZERO
SET
0 0 0 0 0 0 0 0
1
2
3
3
4567
8
9
10
Modulated
Signal Source RF Voltmeter
Rotary Attenuators
Set to Loop Reference Settings
0.1 dB/Div. 1.0 dB/Div. 10 dB/Div.
All cables are 50 Ohm
coaxial. Double shielded
cables preferred.
UG914/U
Female-Female
Connector
10 dB Attenuator Pads
50 Ohm Adaptor
Figure 12: Setting loop adjustment reference level.
tom cavity of the T-Pass stack. Detailed procedu r es and illus t rations follow o n the nex t few
pages.
5) UG-914/U, BNC(F)-BNC(F), union. TX RX Systems' part # 8-5805.
6) UG-28A/U, N(F), N(F), N(F) tee.
CAVITY LOSS SETTING PROCEDURE 1
This procedure uses precision rotary attenuators, a
signal generator and an RF Millivolt meter.
Required Test Equipment
1) Signal generator capable of producing a CW
signal level of at least -10 dBm with variable
output level capability at the frequency of interest.
2) An RF voltmeter with a 0.001 Volt (-50 dBm)
scale and a 50 Ohm input adapter. Helper
Instruments RF millivolter used for this example.
3) Rotary Attenuators, 1@ 0-1 dB in 0.1 dB increments. 1@ 0-10 dB in 1.0 dB increments. 1@
0-70 dB in 10 dB increments. JFW Industries
model 50BR-017.
4) Two 10 dB fixed attenuator pads with BNC connectors. JFW Industries model 50F-010.
7) UG-57B/U, N(M)-N(M) coupling.
8) Two, UG-201A/U BNC(F)-N(M) adapter. TX RX
Systems' part # 8-5814.
9) 50 ohm coaxial cable test leads with BNC male
connectors (high quality cable).
A spectrum analyzer may be used in place of the
RF voltmeter. However, the personnel doing the
work should fully understand the procedure and
understand the use of the analyzer for this applicati on. We have fo und i t convenient to use test
cables with BNC connectors. They allow for more
convenient connection to test equipment and to
small attenuator pads. UG-201 BNC to N adapters
are used when connections to N connectors are
needed.
Procedure for T-Pass Loop
1) Set the signal generator for the desired operating frequency (within 1 MHz of operating frequency) and for an output signal level of
approximately -10 dBm. Set the rotary attenua-
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 17
tors for the Reference Notch Depth Value
Modulated
Signal Source RF Voltmeter
Rotary Attenuators
Set to Loop Reference Settings
0.1 dB/Div. 1.0 dB/Div. 10 dB/Div.
50 Ohm Adaptor
UG-28A/U
UG-57B/U
T-Pass
Loop
10 dB Pad 10 dB Pad
Short Circuit Connector
3-1268 from top of rack
Bandpass Loop turned upside down
with connector inserted into cavity.
Loop visible and screws tight.
Figure 13: Setting the T-Pass loop using step attenuators.
shown in the chart (table 4) for the desired
insertion loss and T-Pass loop part #.
2) Connect the test leads together through the
female union, as shown in Figure 12, and
adjust the range switch and the zero set on the
voltmeter for a convenient reference level (A
level of 2 on the 0 to 3 scale for example) on the
meter. The generator output level may also be
adjusted slightly if necessary.
3) Remove the bandpass loop from the cavity and
insert it, connector end first, back into the cavity
and tighten all 3 screws securely. See Figure
13.
4) Set all three attenuators for 0 dB but leave them
in the circuit.
5) Connect a UG-28A/U Tee connector and UG57B/U coupling to the T-Pass loop as shown in
figure 13. Then connect the test leads as
shown. Make sure to install the short circuit stub
(part # 3-2330) from the top of the T-Pass rack
if the loop does not have an internal short.
6) Loosen the main tuning rod locking screw and
slowly slide the tuning rod in or out to obtain a
dip (minimum voltage) in the meter reading
which indicates cavity resonance. Use the fine
tuning control to maximize the dip (the fine tuning rod should not be full in or out which would
indicate that slight adjustment of the main tuning rod is necessary). Note the meter reading.
7) If the meter reading is greater or less than the
reference level from step 3, the T-Pass loop
rotation will have to be adjusted. If the meter
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 18
Modulated
Signal Source RF Voltmeter
Rotary Attenuators
Set to Loop Reference Settings
0.1 dB/Div. 1.0 dB/Div. 10 dB/Div.
50 Ohm Adaptor
UG-28A/U
UG-57B/U
Bandpass
Loop
10 dB Pad 10 dB Pad
Previously calibrated T-Pass Loop 3-1268
short circuit removed.
Small Circle on Bandpass Loop indicates
ground end of loop and should be
oriented as shown.
Figure 14: Setting the Bandpass loop using step attenuators.
reading is greater than the reference level, the
loop will have to be rotated so that the calibration mark on the loop points to a slightly higher
number on the calibration index label. Conversely, if the meter reading is less than the reference, the loop will have to be rotated so that
the index mark points to a slightly lower number
on the calibration index. Loosen the three loop
locking screws and rotate the loop so that the
index mark is moved to the next higher or lower
calibration tag number as needed and tighten
the 3 locking screws. Note that tight screws are
necessary for accuracy.
8) Repeat steps 6 and 7 until the minimum meter
reading is equal to the reference level from step
3. Rotation of loops will change the cavity frequency slightly.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 19
9) The Bandpass loop should be installed with the
connector up and the ground point circle oriented toward the center of the cavity as shown
in Figure 14.
10) Remove the short circuit stub from the T-Pass
loop.
Procedure for Bandpass Loop
1) Maintain the previous signal generator settings
and set the rotary attenuators for the proper setting as shown in table 4 for the Bandpass Loop.
2) Connect the test leads together through the
female union and adjust the range switch and
the zero set on the voltmeter for a reference
level (A level of 2 on the 0 to 3 scale is conve-
nient) on the meter. See figure 12. The genera-
tor output level may also be adjusted slightly if
convenient.
Required Test Equipment
1) Spectrum Analyzer and a signal generator.
3) Set all three attenuators for 0 dB but leave them
in the circuit.
4) Connect a UG-107 Tee and the UG-57B/U to
the Bandpass loop as shown on figure 14. Then
connect the test leads as shown. Make sure the
short circuit stub has been removed from the TPass loop.
5) Loosen the main tuning rod locking screw (see
figure 8) and slowly slide tuning rod in or out to
obtain a dip (minimum voltage) in the meter
reading which indicates cavity resonance. Use
the fine tuning control to maximize the dip (the
fine tuning rod should not be full in or out which
would indicate that slight adjustment of the
main tuning is necessary). Note the meter reading.
6) If the meter reading is greater or less than the
reference level from step 2, the bandpass loop
rotation will have to be adjusted. If the meter
reading is greater than the reference level, the
loop will have to be rotated so that the calibration mark on the loop, points to a slightly higher
number on the calibration index label. Conversely, if the meter reading is less than the reference, the loop will have to be rotated so that
the index mark points to a slightly lower number
on the calibration index. Loosen the three loop
locking screws and rotate the loop so that the
index mark is moved to the next higher or lower
calibration tag number as needed and tighten
the 3 locking screws. Note that tight screws are
necessary for accuracy.
7) Repeat steps 5 and 6 until the minimum meter
reading is equal to the reference level from step
3. Rotation of loops will change the cavity frequency slightly.
2) Two 10 dB fixed attenuator pads with BNC
connectors. JFW Industries model 50F-010.
3) UG-914/U, BNC(F)-BNC(F), union. TX RX Systems' part # 8-5805.
4) UG-28A/U, N(F), N(F), N(F) tee.
5) UG-57B/U, N(M)-N(M) coupling.
6) Two, UG-201A/U BNC(F)-N(M) adapter. TX RX
Systems' part # 8-5814.
7) 50 ohm coaxial cable test leads with BNC male
connectors (high quality cable).
We have found it convenient to use test cables with
BNC connectors. They allow for a more convenient
connection to test equipment and small attenuator
pads. UG-201 BNC to N adapters are used when
connections to N connectors are needed.
Procedure for T-Pass Loop
1) Remove the screws that hold in the bandpass
loop assembly; remove the assembly; invert it
and place it back into the cavity. The coupling
loop will be visible. Install and tighten the three
locking screws.
2) Connect the test leads to the spectrum analyzer; turn it on and let it warm up for at least 30
minutes.
3) Connect the 10 dB attenuator pads to the test
leads. They will remain connected for all subsequent measurements.
4) Note the Reference Notch Depth value for the
T-Pass loop assembly to be adjusted from the
chart, see table 4.
8) Make sure that all the loop locking screws are
tight. The cavity loops are now set and the cavity should now be tuned to the desired fre-
5) Set the spectrum analyzer for the frequency of
the channel of interest (within 5 MHz of actual
operating frequency)
quency as outlined elsewhere in this manual.
6) If the Reference Notch Depth is 8 dB or less
CAVITY LOSS SETTING PROCEDURE 2
This procedure uses a spectrum analyzer, signal
then set the display for a vertical range of 2dB/
div otherwise set it for 10dB/div.
generator, and fixed attenuator pads.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 20
NOTE
UG-28A/U
UG-57B/U
T-Pass
Loop
10 dB Pad10 dB Pad
Short Circuit
Connector 3-1268
from top of rack
Bandpass Loop
turned upside down
with connector
inserted into cavity.
Loop visible and
screws tight.
Spectrum Analyzer
Bird SignalHawk
Signal Generator
Figure 15: Setting a T-Pass loop for a specific cavity insertion loss.
7) Temporarily connect the test leads from the
spectrum analyzer together through a UG-914
BNC union to set the zero reference.
8) Connect a UG-28 tee and a UG-57 coupling to
the T-Pass loop as shown in Figure 15.
9) Connect the test leads from the spectrum ana-
The tightness of the locking screws
affe c ts t h e de p t h o f the rejecti o n
notch slightly. It is usually necessary
to rotate the loop for a notch depth
that is slightly less than the reference.
The Notch depth will tend to increase
slightly as all three locking screws are
tightened.
lyzer to the tee connector as shown in figure 15.
12) Remove the bandpass loop and place it back
10) Adjust the cavities main tuning rod so that a
rejection notch appears in the center of the display.
into the cavity with the connector-end up.
Procedure for Bandpass loop
1) The Bandpass loop should be installed with the
11) Loosen the three loop locking screws and
rotate the loop to obtain the reference notch
depth from step 4.
connector up and the ground point circle oriented toward the center of the cavity as shown
in Figure 16.
2) Connect the test leads, with 10 dB pads
attached, to the spectrum analyzer; turn it on
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 21
NOTE
10 dB Pad 10 dB Pad
UG-28A/U
UG-57B/U
Bandpass
Loop
Previously calibrated
T-Pass Loop 3-1268
short circuit removed.
Small Circle on
Bandpass Loop
indicates ground
end of loop and
should be oriented
as shown.
Spectrum Analyzer
Bird SignalHawk
Signal Generator
Figure 16: Setting a Bandpass loop for a specific cavity insertion loss.
and let it warm up for at least 30 minutes if this
has not been done.
3) Note the Reference Notch Depth value for the
Bandpass loop assembly to be adjusted from
table 4.
4) Set the spectrum analyzer for the frequency of
the channel of interest (within 5 MHz of actual
7) Connect a UG-28 tee and a UG-57 coupling to
the bandpass loop as shown in figure 16.
8) Connect the test leads from the spectrum analyzer to the tee connector as shown in figure 16.
9) Adjust the cavities main tuning rod so that a
rejection notch appears in the center of the display.
operating frequency).
10) Loosen the three loop locking screws and
5) If the Reference Notch Depth is 8 dB or less
then set the display for a vertical range of 2dB/
div otherwise set it for 10dB/div.
6) Temporarily connect the test leads from the
spectrum analyzer together through a UG-914
BNC union to set the zero reference. Make sure
to use the 10 dB pads which should remain on
the test cables for all measurements.
rotate the loop assembly to obtain the reference notch depth from step 3.
The tightness of the locking screws
affe c ts t h e de p t h o f the rejecti o n
notch slightly, it is usually necessary
to rotate the loop for a notch depth
that is slightly less than the reference.
The Notch depth will tend to increase slightly as all
three locking screws are tightened.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 22
11) Tighten all loop locking screws. The cavity loss
is now set. The cavity will have to be tuned to
its operating frequency following the procedures outlined earlier in this manual.
MAINTENANCE
Because T-Pass transmit ter multicouplers are
composed of mostly passive components, they will
continue to operate without any maintenance for
years and there is no recommended maintenance
period. We do feel, however, that it is wise to check
multicoupler performance by measuring channel
loss periodically and this may be done at any convenient time along with other radio system maintenance.
ISOLATORS
Isolators perform two important functions. Their primary function is to keep unwanted RF frequencies
out of the transmitter so that intermodulation products cannot be generated. Isolators have a substantial amount of reverse isola tion. They also
ensure that the transmitter never sees any significant reflected power so it will always operate with
maximum stability at full-power output. Isolators
prevent energy from getting into the transmitters
output by dumping any RF energy entering the output of the isolator into a dummy load. The model
73-90-11 series of T-pass transmit combiners will
use either single section or dual section isolators at
the input to each T-pass channel.
Single-section isolators have one load port. A properly sized load capable of dissipating the maximum
expected reflected power that might be encountered should be used. Dual section isolators have
two load ports, one for each section. Although
loads of equal power rating may be used for both
ports, it is customary to use an output load capable
of dissipating the maximum expected reflected
power that might be encountered. A small load (5
watts) is usually factory installed on the first section
of the isolator where high reflected power is not a
factor. Refer to Appendix A for a further discussion of isolators.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 23
GENERAL DESCRIPTION
Appendix A
800 MHz Isolators (Compact Style)
TXRX
Systems
Part #
Freq
Range
(MHz)
Isolation
(dB)
(min)
Insertion
Loss
(dB) (max)
3-22223P 764 - 776 50 0.50
3-22224P 794 - 806 50 0.50
3-22225P 806 - 824 50 0.50
3-22226P 851 - 869 50 0.50
3-22227P 870 - 894 50 0.50
3-22228P 925 - 935 50 0.50
3-22229P 935 - 940 50 0.50
3-22230P 940 - 960 50 0.50
3-22223PL 764 - 776 50 0.50
3-22224PL 794 - 806 50 0.50
3-22225PL 806 - 824 50 0.50
3-22226PL 851 - 869 50 0.50
3-22227PL 870 - 894 50 0.50
3-22228PL 925 - 935 50 0.50
3-22229PL 935 - 940 50 0.50
3-22230PL 940 - 960 50 0.50
TXRX
Systems
Part #
Freq
Range
(MHz)
Isolation
(dB)
(min)
Insertion
Loss
(dB) (max)
3-22223PLA 764 - 776 50 0.50
3-22224PLA 794 - 806 50 0.50
3-22225PLA 806 - 824 50 0.50
3-22226PLA 851 - 869 50 0.50
3-22227PLA 870 - 894 50 0.50
3-22228PLA 925 - 935 50 0.50
3-22229PLA 935 - 940 50 0.50
3-22230PLA 940 - 960 50 0.50
3-22223PLB 764 - 776 50 0.50
3-22224PLB 794 - 806 50 0.50
3-22225PLB 806 - 824 50 0.50
3-22226PLB 851 - 869 50 0.50
3-22227PLB 870 - 894 50 0.50
3-22228PLB 925 - 935 50 0.50
3-22229PLB 935 - 940 50 0.50
3-22230PLB 940 - 960 50 0.50
Table A1: Specification for 800 MHz Isolators (Compact Style).
Isolators perform two important functions. Their primary function is to keep other RF frequencies out
of the transmitter so that intermodulation products
cannot be generated. Isolators have a substantial
amount of reverse isolation. They also insure that
the transmitter never sees any significant reflected
power so it will always operate with maximum stability at full-power output. Isolators prevent energy
from getting into the transmitters output stage by
dumping reflected RF energy entering the output of
the isolator into a dummy load.
The 800 MHz (compact style) isolators available
from TXRX Systems are broad-band and do not
require tuning. The isolators are available as either
single section or dual section models. Dual section
models consist of two single sections mounted in
the same case with a load permanently attached to
the load port of the first section. Table A1 lists the
800 MHz isolators available from TX RX Systems
along with their performance specifications.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 24
INSTALLATION
The isolators can be mounted on most types of
su rfac e s but should not be physica l ly located
where they will not be exposed to moisture or very
high humidity. TXRX Systems isolators are well
shielded magnetically and may be mounted on
steel cabinets or panels.
Th e i solators can get quit e h ot
during operation. This can occur
when an antenna system component fails causing high reflected
power which is then dissipated by
the isolator load. These loads can
get hot enough to burn skin so
use caution when servicing these
systems.
VERIFYING ISOLATOR FUNCTIONALITY
If you suspect there may be a problem with an isolator you can verify the functionality of the device
by measuring its reverse isolation and insertion
loss. It is important to electrically remove the isolator from the system before testing. This is easily
accomplished by disconnecting the input and output cables.
WARNING: Do not make or break
cable c on n ections to t h e isola t o r
while th e circuit is un der transmit
power. Shu t down the transm i tter
before servicing.
RECOMMENDED TEST EQUIPMENT
The following equipment or it’s equivalent is recommended when verifying isolator functionality.
1) Spectrum Analyzer. Bird Technologies Signal
Hawk.
2) A pair of double shielded coaxial cable test
leads (RG142 B/U or RG223/U).
3) 50 Ohm load with at least -35 dB return loss
(1.10 : 1) VSWR.
Measuring Reverse Isolation (S12)
The reverse isolation of your isolator can be verified by performing the following procedure in a
step-by-step fashion.
2) Disconnect the input and output cable to the
isolator.
3) Connect a spectrum analyzer and tracking generator to the input and output ports of the isolator respectively, as shown in Figure A1.
4) Make sure that a 50 Ohm load is connected to
the load port of the isolator. If you are testing
the isolator on the bench make sure you connect a load. If you are testing the isolator while it
is still mounted on the system rack/cabinet
leave the existing load connected.
5) Inject a test signal (-10 dBm) from the tracking
generator into the output port of the isolator.
The test signal should sweep across the operating bandwidth of the isolator.
6) Compare your displayed waveform against the
example shown in Figure A3 as well as the
specification listed in table A1.
Measuring Insertion Loss (S21)
The insertion loss of your isolator can be verified
by performing the following procedure in a step-bystep fashion.
1) Make sure the transmitter associated with the
isolator is turned off.
2) Disconnect the input and output cable to the
isolator.
3) Connect a tracking generator and spectrum
analyzer to the input and output ports of the isolator respectively, as shown in Figure A2.
4) Make sure that a 50 Ohm load is connected to
the load port of the isolator. If you are testing
the isolator on the bench make sure you connect a load. If you are testing the isolator while it
is still mounted on the system rack/cabinet
leave the existing load connected.
5) Inject a test signal into the input of the isolator
from the tracking generator which will sweep
across the operating bandwidth of the isolator.
The strength of the test signal should be -10
dBm.
1) Make sure the transmitter associated with the
isolator is turned off.
6) Compare your displayed waveform against the
example shown in Figure A4 and the specification listed in table A1.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 25
Tracking Generator
Spectrum Analyzer
Bird SignalHawk
50 Ω Load
Figure A2: Verifying Insertion Loss.
Tracking Generator
Spectrum Analyzer
Bird SignalHawk
50 Ω Load
Figure A1: Verifying Reverse Isolation.
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 26
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 27
Figure A4: Typical insertion loss waveform.
Figure A3: Typical reverse isolation waveform.
CELCIUS FAHRENHEIT
105 221.0
104 219.2
103 217.4
102 215.6
101 213.8
100 212.0
99 210.2
98 208.4
97 206.6
96 204.8
95 203.0
94 201.2
93 199.4
92 197.6
91 195.8
90 194.0
89 192.2
88 190.4
87 188.6
86 186.8
85 185.0
84 183.2
83 181.4
82 179.6
81 177.8
80 176.0
79 174.2
78 172.4
77 170.6
76 168.8
75 167.0
74 165.2
73 163.4
72 161.6
71 159.8
70 158.0
69 156.2
68 154.4
67 152.6
66 150.8
65 149.0
64 147.2
63 145.4
62 143.6
61 141.8
60 140.0
59 138.2
58 136.4
57 134.6
56 132.8
55 131.0
54 129.2
53 127.4
52 125.6
51 123.8
50 122.0
49 120.2
48 118.4
47 116.6
46 114.8
45 113.0
44 111.2
43 109.4
42 107.6
41 105.8
40 104.0
39 102.2
38 100.4
37 98.6
36 96.8
35 95.0
34 93.2
33 91.4
32 89.6
31 87.8
30 86.0
29 84.2
28 82.4
CELCIUS FAHRENHEIT
27 80.6
26 78.8
25 77.0
24 75.2
23 73.4
22 71.6
21 69.8
20 68.0
19 66.2
18 64.4
17 62.6
16 60.8
15 59.0
14 57.2
13 55.4
12 53.6
11 51.8
10 50.0
9 48.2
8 46.4
7 44.6
6 42.8
5 41.0
4 39.2
3 37.4
2 35.6
1 33.8
0 32.0
-1 30.2
-2 28.4
-3 26.6
-4 24.8
-5 23.0
-6 21.2
-7 19.4
-8 17.6
-9 15.8
-10 14.0
-11 12.2
CELCIUS FAHRENHEIT
-12 10.4
-13 8.6
-14 6.8
-15 5.0
-16 3.2
-17 1.4
-18 -0.4
-19 -2.2
-20 -4.0
-21 -5.8
-22 -7.6
-23 -9.4
-24 -11.2
-25 -13.0
-26 -14.8
-27 -16.6
-28 -18.4
-29 -20.2
-30 -22.0
-31 -23.8
-32 -25.6
-33 -27.4
-34 -29.2
-35 -31.0
-36 -32.8
-37 -34.6
-38 -36.4
-39 -38.2
-40 -40.0
-41 -41.8
-42 -43.6
-43 -45.4
-44 -47.2
-45 -49.0
-46 -50.8
-47 -52.6
-48 -54.4
-49 -56.2
-50 -58.0
CELCIUS FAHRENHEIT
Celsius to Fahrenheit Conversion Table
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 28
Return Loss vs. VSWR
Return Loss VSWR
30 1.06
25 1.11
20 1.20
19 1.25
18 1.28
17 1.33
16 1.37
15 1.43
14 1.50
13 1.57
12 1.67
11 1.78
10 1.92
9 2.10
Watts to dBm
Watts dBm
300 54.8
250 54.0
200 53.0
150 51.8
100 50.0
75 48.8
50 47.0
25 44.0
20 43.0
15 41.8
10 40.0
5 37.0
4 36.0
3 34.8
2 33.0
1 30.0
dBm = 10log P/1mW
Where P = power (Watt)
Insertion Loss
Input Power (Watts)
50 75 100 125 150 200 250 300
3 25 38 50 63 75 100 125 150
2.5 28 42 56 70 84 112 141 169
2 32 47 63 79 95 126 158 189
1.5 35 53 71 88 106 142 177 212
1 40 60 79 99 119 159 199 238
.5 45 67 89 111 134 178 223 267
Output Power (Watts)
Insertion Loss
Free Space Loss
Distance (miles)
.25 .50 .75 1 2 5 10 15
150 68 74 78 80 86 94 100 104
220 71 77 81 83 89 97 103 107
460 78 84 87 90 96 104 110 113
860 83 89 93 95 101 109 115 119
940 84 90 94 96 102 110 116 120
1920 90 96 100 102 108 116 122 126
Free Space Loss (dB)
Free space loss = 36.6 + 20log D + 20log F
Where D = distance in miles and F = frequency in MHz
Frequency (MHz)
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 29
TX RX Systems Inc. Manual 7-9100-5 10/17/11 Page 30
8625 Industrial Parkway, Angola, NY 14006 Tel: 716-549-4700 Fax: 716-549-4772 sales@birdrf.com www.bird-technologies.com
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