Agilent 776D Service Manual

776D Dual Directional Coupler

Operating and Service
Manual

Manual part number: 00776-90010
Printed in USA
May 2001
Supersedes: June 2000

Revision 3.1

Notice

The information contained in this document is subject to change without
notice.

Agilent Technologies makes no warranty of any kind with regard to this
material, including, but not limited to, the implied warranties of
merchantability and fitness for a particular purpose. Agilent Technologies
shall not be liable for errors contained herein or for incidental or
consequential damages in connection with the furnishing, performance, or
use of this material.

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its software on equipment that is not furnished by Agilent Technologies.

This document contains proprietary information which is protected by
copyright. All rights are reserved. No part of this document may be
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written consent of Agil ent Technologies.

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R
Use, duplication, or disclosure by the U.S. Government is subject to

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Data and Computer Software clause at DFARS 252.227-7013 for DOD
agencies, and subpara graphs (c)(1) and (c)(2) of the Commercial Computer
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Agilent Technologies, Inc.
1400 Fountaingrove Parkway
Santa Rosa, CA 95403-1799, U.S.A.

© Copyright 2000-2001 Agilent Technologies, Inc.

ii Agilent 776D Operating And Service Manual

In This Manual…

Overview, page 1

•

• Specifications, page 3

• Installation, page 4

• Storage and Shipment, page 6

• Performance Tests, page 7

Agilent 776D Operating And Service Manual iii

Warranty

Custom systems are warranted by contractual agreement between Agilent
Technologies and the customer.

Certification Agilent Technologies, Inc., certifies that this product met its published

specifications at the time of shipment from the factory. Agilent Technologies
further certifies that its calibration measurements are traceable to the
United States National Institute of Standards and Technology (NIST,

formerly NBS), to the extent allowed by the Institute’s calibration facility,
and to the calibration facilities of other International Standards
Organization members.

Warranty This Agilent Technologies system product is warranted against defects in

materials and workmanship for a period corresponding to the individual
warranty periods of its component products. Instruments are warranted for a
period of one year . During the w arranty period, Agile nt T echnol ogies will, at
its option, either repair or replace products that prove to be defective.

Warranty service for products installed by Agilent Technologies and certain
other products designated by Agilent Technologies will be performed at

Buyer’s facility at no charge within Agilent Technologies service travel
areas. Outside Agilent Technologies service travel areas, warranty service
will be performed at Buyer’s facility only upon Agilent Technologies’ prior
agreement and Buyer shall pay Agilent Technologies’ round trip travel
expenses. In all other areas, products must be returned to a service facility
designated by Agilent Technologies.

For products returned to Agilent Technologies for warranty service, Buyer
shall prepay shipping charges to Agilent Technologies and Agilent
Technologies shall pay shipping charges to return the product to Buyer.
Howev er , Buyer sh all pay all ship ping char ges, duti es, and taxe s for products
returned to Agilent Technologies from another country.

Agilent Technologies warrants that its software and firmware designated by
Agilent Technologies for use with an instrument will execute its
programming instructions when properly installed on that instrument.
Agilent Technologies does not warrant that the operation of the instrument,
or software, or firmware will be uninterrupted or error free.

LIMITATION OF WARRANTY. The forego ing warranty shall not apply
to defects resulting from improper or inadequate maintenance by Buyer,
Buyer-supplied softwa re or interfacing, unauthorized modification or
misuse, operation outside of the environmental specifications for the
product, or improper site preparation or maintenance.

iv Agilent 776D Operating And Service Manual

NO OTHER WARRANTY IS EXPRESSED OR IMPLIED. AGILENT
TECHNOLOGIES SPECIFICALLY DISCLAIMS THE IMPLIED
WARRANTIES OR MERCHANTABILITY AND FITNESS FOR A
PARTICULAR PURPOSE.

EXCLUSIVE REMEDIES. THE REMEDIES PROVIDED HEREIN ARE

BUYER’S SOLE AND EXCLUSIVE REMEDIES. AGILENT
TECHNOLOGIES SHALL NOT BE LIABLE FOR ANY DIRECT,
INDIRECT, SPECIAL, INCIDENTAL, OR CONSEQUENTIAL
DAMAGES, WHETHER BASED ON CONTRACT, TORT, OR ANY
OTHER LEGAL THEORY.

YEAR 2000. Agilent Technologies warrants that each Agi l ent Technologies
hardware, software, and firmware product on Agilent Technologies’
Corporate Price List (dated July 1, 1998 or later) delivered under the
product’s contract of sale will be able to accurately process date data
(including, but not limited t o, calculating, c omparing, and sequenc ing) from,
into, and between the twentieth and twenty-first centu ries, and the years
1999 and 2000, including leap year calculations, when used in accordance
with the product documentation provided that all other products (that is,
hardware, software, firmware) used in combination with such Agilent
Technologies product(s) properly exchange date data with it. If the
agreement requires that specific Agilent Technologies products must
perform as a system in accordance with th e foregoing warranty, then that
warranty will apply to those Agi le n t Tec hnol ogies products as a system, and
Customer retains sole responsibility to ensure the year 2 000 readiness of its
information technology and business environment. The duration of this
warranty extends through January 31, 2001.

The remedies available under thi s warranty wi ll be defined i n, and subjec t to,
the terms and limitations of the warranties contained in the contract of sale.
To the extent permitted by local law, this warranty applies only to branded
Agilent Technologies products and not to products manufacture by others
that may be sold or distributed by Agilent Technologies. N othing in this
warranty will be construed to limit any rights or remedies provided
elsewhere in the contract of sale with respect to matt ers other than year 2000
compliance.

Assistance Product maintenance agreements and other customer assistance agreements

are available for Agilent Technologies products.
For assistance, call your local Agilent Technologies Sales and Ser vice Office

(refer to “Service and Support Any adjustment, maintenance, or repair of
this product must be performed by qualified personnel. C ontact your
customer engineer through your local Agilent Technologies Service Center.
You can find a list of local service representatives on the Web at the address
below.” on pagevi).

Agilent 776D Operating And Service Manualv

Service and Support

Any adjustment, maintenance, or repair of this product must be
performed by qualified personnel. Contact your customer engineer
through your local Agilent Technologies Service Center. You can find a

list of local service representatives on the Web at the address below.

Online assistance: www.agilent.com/find/assist
United States

(tel) 1 800 452 4844

New Zealand

(tel) 0 800 738 378
(fax) ([phone]

Country Phone Number Fax Number

Singapore 1-800-375-8100 (65) 836-0252
Malaysia 1-800-828-848 1-800-801664
Philippines (632) 8426802

Thailand [phone] (outside Bangkok)

Hong Kong 800-930-871 (852) 2506 9233
Taiwan 0800-047-866 (886) 2 25456723

Latin America

(tel) [phone]
(fax) [phone]

Japan

(tel) ([phone]
(fax) ([phone]

Asia Call Center Numbers

1-800-16510170 (PLDT Subscriber
Only)

[phone] (within Bangkok)

Canada

(tel) 1 877 894 4414
(fax) [phone]

Australia

(tel) 1 800 629 485
(fax) ([phone]

(632) 8426809
1-800-16510288 (PLDT
Subscriber Only)

(66) 1-661-3714

Europe

(tel) ([phone]
(fax) ([phone]

People’s Republic of
China

India 1-600-11-2929 000-800-650-1101

800-810-0189 (preferred)
10800-650-0021

10800-650-0121

vi Agilent 776D Operating And Service Manual

Safety and Regulatory Information

Review this product and related documentation to familiarize yourself with
safety markings and instructions before you operate the instrument. This
product has been designed and tested in accordance with international
standards.

WARNING The WARNING notice denotes a hazard. It calls attention to a procedure,

practice, or the like, that, if not correctly performed or adhered to, could result
in personal injury. Do not proceed beyond a WARNING notice until the
indicated conditions are fully understood and met.

CAUTION The CAUTION notice denotes a hazard. It calls attention to an operating

procedure, practic e, o r the like, which, if not correctly pe rformed or adhered
to, could result in da mage to the product or loss of important data. Do not
proceed beyond a CAUTION notice until the indicated conditions are fully
understood and met.

Instrument Markings

When you see this symbol on your instrument, you should refer to the instrument’s

!

1SM1-A This text indicates that the instrument is an Industrial Scientific and Medical Group 1

instruction manual for important information.

This symbol indicates hazardous voltages.

The laser radiation symbol is marked on products that have a laser output.

This symbol indicates that the instrument requires alternating current (ac) input.

The CE mark is a registered trademark of the European Community. If it is
accompanied by a year, it indicates the year the design was proven.

The CSA mark is a registered trademark of the Canadian Standards Association.

Class A product (CISPER 11, Clause 4).
This symbol indicates that the power line switch is ON.

This symbol indicates that the power line switch is OFF or in STANDBY position.

Agilent 776D Operating And Service Manual vii

Safety Earth Ground

This is a Safety Class I product (provided with a protective earthing
terminal). An uninterrup ti ble saf et y ear th gr ound must be pr o vided from the
main power source to the product input wiring terminals, power cord, or
supplied power cord set. Whenever it is likely that the protection has been
impaired, the product m ust be made inoperative and secured against any
unintended operation.

Befor e Applying Power Verify th at the product is configured to match the available main power

source as d escribed in the input power configuration in structions in this
manual. If this product is to be powered by autotransformer, make sure the
common terminal is connected to the neutral (grounded) side of the ac power
supply.

viii Agilent 776D Operating And Service Manual

Overview

This operating note contains operating information for the Agilent 776D
dual directional coupler. Since the 776D must be returned to Agilent
Technologies for repair, no service information is given. I nstrument
specifica ti ons are listed in Table 1. These specifications ar e the performance
standards, or limits agains t which the instrument may be te sted. Figure 1
defines the terms used in Table 1 and throughout this manual.

Figure 1 Coupler Terminology

Description The 776D is a dual directional coupler desi gned for use in 50-ohm coaxial

systems. In this coupler, nominal coupling is 20 dB. The coupling variation
with frequency of each auxiliary arm is marked on the namepl ate opposite
the appropriate auxiliar y arm.

Agilent 776D Operating and Service Manual 1

Overview

Network Analyzer

Reflectometer

Fixed Frequency

Reflectometer

Swept Frequency

Reflectometer

A network analyzer with either phase magnitude display, phase gain display
or polar display, with a sweep generator with appropriate RF unit plug-in,
may be used with the 776D as a reflectometer test setup. The network
analyzer reflectometer may be used either for fixed frequency or swept
frequency measurements.

A SWR meter with a sweep oscillator, with appropriate plug-in RF unit, or
other signal source may be used with the 776D as a fixed frequency
reflectometer.

A frequency response test set or network analyzer system together with a
sweep oscillator wit h appropri ate plu g-ins may be use d as a swept freq uenc y
reflectometer.

A SWR meter with a sweep oscillator and a 140 or 180 oscilloscope with
appropriate plug-ins may be used as a swept frequency reflectometer.

2 Agilent 776D Operating and Service Manual

Specifications

Table 1 Specificati ons

Characteristics Value

Primary line insertion loss Approximately 0.35 dB maximum
Minimum directivity
Nominal coupling attenuation (each secondary arm) 20 dB
Accuracy of coupling (each secondary arm) Mean coupling 20 dB + 0.5 dB

1

40 dB

Specifications

Maximum coupling variation (each secondary coupling
value)

Auxiliary arm tracking
Maximum primary line VSWR
Maximum auxiliary arm VSWR 1.20
Primary line power handling capacity 50 watts average or 10 kW peak
Primary line connector

Auxiliary arm connectors

Accessories available Agilent 11511A Type N Female Shorting

Dimension 6-5/16 in x 2-5/16 in x 1-3/4 in

Net weight 2 lb (0.9 kg)

1. Measured with Agilent sliding load.

2. Maximum change in coupling curve of one secondary arm relative to the other.

3. Agilent Type N connectors mate with standard Type N connectors (see text)

2

1

3

3

± 1 dB of specified mean coupling value

Equal to or less than 0.3 dB

1.15

Agilent compatible Type N connectors, one
male and one female

Agilent compatible Type N connectors,
female

Jack
Agilent 11512A Type N Male Shorting Plug

(161 mm x 59 mm x 45 mm)

Agilent 776D Operating and Service Manual 3

Installation

Installation

Initial Inspection Inspect the shipping container for damage. If the shipping container or

cushioning material is damaged, it should be kept until the cont ents of the
shipment have been checked for completeness and the instrument has been
checked mechanically and electrically. Procedures for checking electrical
performance are given in "“Performance Tests” on page 7". If the contents

are incomplete, if there is mechanical damage or defect, or if the instrument
does not pass the electrical performance test, notify the nearest Agilent
Technologies office. If the shipping container
material sh ows signs of stre ss, notify th e carrier as well as the Agilent
Technologies office. Keep the shipping materials for the carrier's inspection.
The Agilent of f ice will ar range for repai r or re place ment without wa itin g for
claim settlement.

is damaged, or the cu shi oni ng

Mating Connectors Type N mating connectors used with the 776D should have dimensions

compatible with US Military Standard MIL-C-39012.

N-female Pin Depth: +0.207 inches to +0.201 inches

(effective 0 to–0.006 inches)

N-male Pin Depth: –0.207 inches to –0.213 inches

(effective 0 to –0.006 inches)

Operating Environment

CAUTION Do not heat cycle t his coupl er during use or stor age. K eep coupl er near r oom

Operate the 776D in the range from 0 °C to +55 °C and protect it from
excessive humidity.

temperature (25 °C).

Installation Instructions

Support Weight When installing the 776D, be sure the auxilliary equip me nt supports its own

weight. The coupler, particularly the connectors are not designed to support
weight.

4 Agilent 776D Operating and Service Manual

Installation

CAUTION Do not drop the coupler . While the coupler probabl y with not break, it can be

jarred out of adjustment and the connectors can be damaged.

On the bottom of each coupler is supported by four pl ast i c feet (part number
0361-0207). The feet are insert s in 8-32 tapped holes (0.50 in deep) and may
be removed to mount the coupler. Dimensions between mounting holes are
shown in Figure 2.

Figure 2 Dimensions of Trapped Mounting Holes

Signal Flow Signal flow is indicated in Figure 3. Coupling is indicated by arrows. The

776D is bi-directional (signal may go through the coupler in either
direction).

Figure 3 Type N Connector Dimensions

Agilent 776D Operating and Service Manual 5

Storage and Shipment

Storage and Shipment

Environment The 776D may be stored in surroundings between –40 °C and +75 °C.

However, heat cycling should be avoided by storing at an even room
temperature (25 °C) if at all possible. The greater the heat cycling, the
greater chance of dimensional c hange of th e printed ci rcuit board resulting i n
out-of-specification operation.

Original Packaging Containers and materials identi cal to those used in factory packaging are

available through Agilent Technologies offices. If the instrument is being
returned to Agilent office for servicing, attach a tag indicating the type of
service required, r eturn add ress, model number , a nd full s erial nu mber . Also,
mark the container FRAGILE to assure careful handling. In any
correspondence, refer to the instrument by model number and full serial
number.

Other Packaging The following general instructions should be used for repackaging with

commercially available materials:

1. Wrap the instrument in heavy paper or plastic. (If shipping to a Agilent
Technologies office or service center, attach a tag indicating the type of
service required, return address, model number, and full serial number.)

2. Use a strong shipping container. A single wall carton made of
200-pound test material is adequat e.

3. Use enough shock-absorbing material (3 to 4-i nch layer) ar ound all sides
of the instrument to provide firm cushion and prevent movement inside
the container.

4. Seal the shipping container securely.

5. Mark the shipping container FRAGILE to assure careful handling.

6 Agilent 776D Operating and Service Manual

Coupling Test

Specification • Mean Coupling, 20 dB ± 0.5 dB

Performance Tests

Perf ormance Tests

The performance tests check the instrument’s electrical performance using
the specifications of Table 1 on page -3 as the performance standards.

• Maximum Coupling Variation, ± l dB of mean coupling.

Figure 4 Coupling Test Setup

Procedure 1. Set up the equipment as shown in Figure 5.

2. Set the SWR meter to maximum bandwidth, 50 dB range.

3. With 1000 Hz square-wave modulation, tune SWR meter FREQ control
for a maximum indication. Set the SWR meter GAIN control for an
indication of 0 dB on the meter.

4. Observe the waveform while sweeping the oscillator manually from 940
to 1900 MHz. If the waveform is not square:

a. Adjust the loop gain of the oscillator. If still not square,
b. Add a 10 dB attenuator to the 20 dB attenuator, and repeat step 4.

5. Adjust the gain of the SWR meter to 0 dB on the 50 dB-NORMAL
range on the SWR meter and run a calibration line on the X-Y recorder.

6. Set level to 0.5 dB and run a calibration line.

7. Set level to 1.0 dB and run a calibration line.

Agilent 776D Operating and Service Manual 7

Performance Tests

8. Set level to 1.5 dB and run a calibration line.

9. Set level to 2.0 dB and run a calibration line.

10. Adjust the gain of the SWR meter for an indication of 1 dB. Remove the
20 dB attenuator and insert the 776D under test, as shown in Figure 4.
Run a test trace. See Figure 5. The test trace should have a variation of

less than ± l dB and the mean couplin g should be be tween 19.5 and 20.5
dB.

11. Reve rse th e 776D un der tes t end- for-e nd an d repeat the te st for coup ling
on the other arm.

Figure 5 Coupling Test Trace

8 Agilent 776D Operating and Service Manual

Directivity Test

Specification: Minimum directivity 40 dB

Performance Tests

Figure 6 Directivity Test Setup

Procedure 1. Connect the equipment as shown in Figure 6, with the Agilent 776D

under test un-terminated.

2. Set the SWR meter to maximum BANDWIDTH, and full gain on the
50 dB range.

3. Modulate the sweep oscillator with 1000 Hz square-wave modulation
and tune the SWR meter FREQ control for a peak indication.

4. Adjust the RF output for a 5 m V signal on the oscilloscope.

5. Manually sweep the oscillator from 940 to 1900 MHz while observing
the waveform. If the waveform does not remain squa re, adjust the ALC
loop gain of the oscillator.

Agilent 776D Operating and Service Manual 9

Performance Tests

6. With the SWR Meter set to the 50 dB-NORMAL range, adjust the
GAIN control to obtain a full-scale (0 dB) indication.

7. Terminate the 776D under test with the coaxial short. Note the SWR
Meter indication. Adjust SWR meter GAIN control to indicate half-way
between this indication and the indication in step 6. This will balance
out any source match errors. The setup is now calibrated.

8. Connect the sliding load in place of the coaxial short.

9. Remove the 40 dB pad from the c rysta l dete ctor a nd reco nnect t he 776D
under test.

10. Manually slowly sweep the oscillator from 940 MHz to 1900 MHz
while rapidly phasing the sl iding l oad. Not e the min imum number of dB
down that the signal indicates on the SWR meter. Be sure to add any
SWR meter range changing and the 40 dB removed by the pa d to the
indicated value. If the indication is more than 40 dB down at all
frequencies, the 776D is within specifications and no further directivity
testing need be done. If not, note the frequencies where the 776D
appears out of specif i ca ti on. (The 776D may not be out of specification.
The directivity signal and the signal reflected from the load may be
adding in-phase.) To find the true directivity, proceed with the following
tests.

11. Set the sweep oscillator for CW operation at the frequency where the
directivity appears to be out of specification. Phase the sliding load and
note the dB attenuation values of the maximum and minimum meter
indications. Record these indications. Subtract the smaller value from
the larger. The remainder is M

. For example, if the indications were

l

–0.5 and 4.4 dB with a pad of 40 dB, the two indications are 39.5 and

44.4 dB down. The difference between the two indications is 4.9 dB
(which is M

).

l

12. Refer to the Sig nal Separatio n Chart in Figure 7. Determine values for

, which are the two correction values to be used. Add the minimum

M

2

dB indication of step 11 to each correction value (M
the differ ence in dB (M

is 4.9 dB, then entering the graph in Figure 7 at

1)

). For example, if

2

4.9 dB on the vertical scale, read the two correction values of 2.1 and

13.3 dB on the horizontal scale. Add these values to the smaller of the
two dB indications. In our example, the corrected results would be 41.6
dB and 52.8 dB. In this case, since both results are better than the
specifications no further tests need be made. However, if one of the
corrected results is out of specifications, proceed to the following tests

13. Two results were determined in step 12. One of these results is the
coupler directivity and one is the load reflection, but it is not

is which. To identify the dire ctivity value from the load reflection

which

known

value, loosen the sliding load center conductor lock and pull out the
center conductor a smal l distance. Tighten the center conductor lock.

10 Agilent 776D Operating and Service Manual

Performance Tests

14. Repeat steps 11 and 12. The corrected result for sliding load reflection
should remain practically the same as the original corrected result (with
a few tenths of a dB). The true 776D directivity is the other original
corrected result, whi ch changed when the sli ding load was l oosened. It is
not intuitively obvious that

loosening the sliding load conductor affects

the directivity value instead of the sliding load value. The re flection
from the added discontinuity due to the loosened conductor adds to the
measured directi vi ty si gnal whi le t he refle ction from t he mo ving p ortio n
of the sliding load has not been changed by loosening the connector.

15. Reverse the 776D under test end-for- end and repeat steps 1 through 14.
This completes the CW directivity test.

16. If a swept frequenc y directi vi ty test i s desire d, an X-Y recorder may also
be used. Connect the Y input of the r ecorde r to the REC OUT conne ctor
on the rear of the SWR meter. Insert a tee connector in the recorder X
input line and connect the itweep oscillator SWEEP OUT signal to the
recorder. Sweep from 940 MHz to 1900 MHz while phasing the sliding
load. For any measurements where a tracking error of 0.3 dB would be
significant, reset the open/short reference at the frequency in question
and re-run the measurement.

Signal Separation Chart The chart shown in Figure 7 is used for separating two signals when their

sums and differences are known.

= difference in dB between the minimum and maximum return loss

M

1

measurements

= correction in dB to be added to smallest dB reading

M

2

If Load Reflection is greater than unknown, use the e
If Load Reflection is less than unknown, use the e

> eun curve.

L

< eun curve.

L

Agilent 776D Operating and Service Manual 11

Performance Tests

Figure 7 Signal Separation Chart

12 Agilent 776D Operating and Service Manual

VSWR Test

Performance Tests

Specification • Maximum Primary Line SWR, 1.15

• Maximum Auxiliary Arm SWR, 1.20

Figure 8 VSWR Test Setup

Procedure 1. Connect the equipment as shown in Figure 8, with the 776D under test

unterminated.

2. Set SWR meter to maximum BANDWIDTH and full gain on the 40 dB
range.

3. Modulate the sweep oscillator with 1000 Hz square-wave modulation
and tune the SWR meter FREQ control for a maximum indication.

4. Set the oscillator RF output for an indication of 0 dB.

5. Manually sweep the oscillator from 940 to 1900 MHz while observing
the wav eform. If w av eform is not square , a. Adjust th e ALC loop gain of
the oscillator. If it cannot be adjusted to be square, b. Replace the 10 dB
leveling pad with a 20 dB pad and repeat step 5.

Agilent 776D Operating and Service Manual 13

Performance Tests

6. Set the CW frequency to approx imately midband (1420 MHz). With the
SWR meter set to the 40 dB range, adjust the GAIN control to full scale
0 dB indication.

7. Terminate the measurement 776D with a coaxial short. Note the
indication. Set the SWR mete r GAIN control to indicate half way
between this indication and the indication in step 6. This procedure will
balance out any source match errors. The setup is now calibrated.

8. Connect the port of the 776D under test as a load on the measurement
776D. Terminate the 776D under test with a sliding load.

9. Remove the 20 dB pad from the crystal detector and reconnect the
measurement 776D.

10. Manually sweep the oscillator slowly from 940 MHz to 1900 MHz
while rapidly phasing th e sliding load. Read the number of dB down th e
signal indicates on the SWR meter. Be sure to add the SWR meter range
changing and the dB removed by the pad to the indicated value.

11. Whenever the value in step 10 approaches 24.5 dB (VSWR of 1.15
measured with a directional coupler directivity of 40 dB, (computed
with a Reflectometer Calculator, obtainable from Agilent, p/n
5952-0948), set for CW o perat ion on t hat f requenc y a nd v ar y the s lidi ng
load. Take the average of the readings as the true value.

12. Reverse the 776D under test end-for- end and repeat steps 1 through 11
on the opposite port of the mainline.

13. To measure the VSWR of the au xil ia ry ar ms, ter m in ate both ports of the
mainline with 50 ohm loads. Connect auxiliary port under test to the
measurement 776D where the mainline port under test was originally
connected. It is not necessary in this case to terminate the unused
auxiliary port or use a sliding load. The indication should be le ss than

21.9 dB (SWR of 1.2 measured with a directional coupler directivity of
40 dB).

14 Agilent 776D Operating and Service Manual