Larcan MX30V, MX30VX User Manual

PUBLICATION TSM 20-332

TECHNICAL MANUAL

30 WATT VHF AMPLIFIER

FOR MX3 0V SERIES

TV TRANSMITTER/TRANSLATOR

LARCAN INC.
228 AMBASSADOR DRIVE
MISSISSAUGA, ONTARIO
CANADA L5T 2J2

PHONE: [phone]
FAX: [phone]

Rev 0: November 26, 1998

MX30V series - 30 Watt VHF AMPLIFIER
Section Title Page

NOTICES, ETC.................................................................3

SAFETY AND HEALTH WARNINGS.....................................4&5

GENERAL SERVICE INFORMATION

1) Parts Lists Explained...................................5

2) Interpreting LARCAN Drawing Numbers.....................5

3) The LARCAN Assembly Prefix Numbering System.............6

4) List of Prefix Numbers for the 10 W Transmitter .........7

5) Production Changes......................................7

INTRODUCTION.....................................................8

GENERAL DESCRIPTION..............................................8

SPECIFICATIONS..................................................10

ABOUT THIS MANUAL...............................................11

PUBLICATIONS LIST for MX30V series VHF Amplifier:

PUB98-29 Installation:

1. General Information ..............................29-1

2. Grounding and Ground Loops .......................29-2

3. Lightning and other Transient Protection .........29-4

4. Power Wiring .....................................29-9

5. Ventilation and Air Conditioning ................29-10

6. Fire Protection .................................29-11

7. Unpacking .......................................29-12

8. Transmitter External Interlock Connections ......29-12

9. On Site: First Time Startup .....................29-13

PUB98-30 Amplifier Chassis (Prefix 1):

1. Amplifier Chassis Description ....................30-1

Comment:

the footer date stamp to
release date,and make sure
that any revisions have the
date stamp the same date as
the revision.

don't forget to set

MX30V series - 30 Watt VHF AMPLIFIER

PUB98-31 RF Output System: Filter and Directional Coupler (Prefixes 6 & 7):

1. HB Helical Resonator Bandpass Filter Description........31-1

2. HB Low Power Bandpass Filter Description................31-3

3. LB Low Pass & Notch Filter Description..................31-4

4. RF Directional Coupler Description......................31-5

PUB98-32 RF Power Amplifier (Prefix 2):

1. Introduction and General Description....................32-1

2. Preamplifier Circuit Board Assembly.....................32-2

3. RF Power Amplifier......................................32-2

PUB98-33 Amplifier Control Board & Metering Panel (Prefix 4):

1. Control Board & Metering Panel Description ..............33-1

2. Amplifier Control Circuit Board Description.............33-2

PUB98-34 Transmitter Output RF Metering Detector Board (Prefix 5) :

1. RF Metering & AGC Board Description.....................34-1

2. RF Metering Board Test and Calibration..................34-2

PUB98-34a Pin Attenuator Board (Prefix 9):

1. Pin Attenuator Board Description.......................34a-1

2. Pin Attenuator Board Setup.............................34a-1

INTRODUCTION

This manual describes the LARCAN 30 watt VHF amplifier designed for NTSC
channels 2 through 13. Models 40D2232G1 is for channels 7 through 13, 40D2232 G2
for channels 2, 3, and 4, and model 40D2232 G3 is for channels 5 and 6. These
amplifiers are used in the LARCAN-USA MX30V series transmitters and translators.

LARCAN all-solid-state 30 W VHF amplifier were designe d to operate conservatively
at 30 W peak sync visual RF power and 3 W average aural single carrier RF power,
with superb performance, reliability and operating economy. This amplifier
accepts an on-channel internally diplexed (in a 10:1 ratio vis to aur) composite
driving signal of about 1mW peak visual RF, as input to its RF chain.

The 30 W amplifier and channel processor chassis' are designed to fit in a
single 19" customer-provided cabinet rack, and require 7" (4RU) of vertical panel
space for a complete transmitter or translator system. Alternatively, a 19"
customer-provided tabletop cabinet could be substituted if the site requires it.

The RF amplifier heatsink has its own integral cooling fan, and other sub­assemblies are convection cooled. The simplicity of design, the deployment of
all modular and other subassemblies, and the use of standard readily available
components, also enhances serviceability.

Peak forward and reflected power are displayed on an analog percent power meter
located on the front panel of the unit.

AMPLIFIER CHAIN

The internally diplexed composite RF output of the channel processor is fed to a
conservatively designed broadband solid-state amplifier. This amplifier requires
no tuning or adjustment. Simplicity of operation, reduced maintenance costs and
increased reliability are a few of the major benefits derived from this
amplifier.

The amplifier chain consists of two stages of amplification for low band and
three stages for high band.

For amplifiers having somewhat more gain than usual, and especially for 10 watt
output applications, the exciter driving the preamplifier may be padded down with
an inline attenuator to avoid overdrive to the preamplifier, because exciters
generally perform better at higher output levels.

The preamplifier uses high gain, broadband, integrated circuit amplifier(s)
operating class A. This preamplifier has two stages in high band models, while a
single stage suffices for low band.

The preamplifier uses the same circuit board that is an integral part of the
"phase quadrature control" that is a required part of paralleled amplifier
configurations. The 30 W transmitter uses a single RF chain, consequently
quadrature phasing is not needed nor used, but some low cost components for it
may remain in place on the board. Removal entails far greater overall expense
than simply leaving them in place.

The PA stage consists of a pair of push-pull FETs in a single case, operating in

class AB as a linear amplifier. This amplifier is capable of more than 50 watts
RF output when driven by the preamplifier in the present system, but uses the
identical dual FET device that is used in higher powered LARCAN transmitters.

The Sound/Aural signal of the transmitter is internally diplexed and corrected at
IF with the visual/vision signal within the exciter, and is amplified in common
with the visual/vision signal in the amplifier chain. Internal diplexing offers
the distinct advantage of lower cost.

The amplifier output is fed through the bandpass filter and the directional
coupler, which provides a small sample of forward and reflected output power for
AGC and VSWR supervisory functions. The transmitter output then passes to the
antenna.

TRANSMITTER CONTROL

The control circuitry in this solid state transmitter is simple. Interlocking in
the 30 W simply consists of jumpers (marked EXT1 and EXT2) but external patch
panel link switches, or RF switching auxiliary contacts, can be connected if
desired. This low power level generally needs no interlocking.

All control wiring of the transmitter passes through a control circuit board
(prefix 4), and facilities are provided on this board for telemetry, st atus, and
control connections to and from a remote control system.

The transmitter interlock wiring is also brought out on terminal block TB2.
External Interlocks 1 and 2 are all brought out on TB2 for connection as
required. Interlock 1 is provided here only for consistency with other LARCAN
transmitter designs in which this interlock is used with a fire alarm system to
shut off blowers.

In the 10 W, the control is so simple (just a single contactor) that either
Interlock 1 or 2 can be used. The cooling fan for the PA heatsink is wired
across the power supply output, therefore will operate whenever the supply is
energized. A thermostat is provided in the PA heatsink to open the interlock
chain should an unlikely overheating condition occur.

On site it is necessary to ensure that AC mains voltage within ±10% of nominal is
available, especially in sites where the voltage can often be extremely variable,
and/or failures are common. It is a good idea to log all voltage excursions in
such sites over a period of time, and then specify a suitable voltage regulator.

It may be necessary to specify a regulator capable of wide input range if site
voltage variations are extreme.

The amplifier's 48Vdc linear power supply (power-one type HD48-3-A) is rated
for 3A and is designed for operation from AC power line voltage variation of
+10%, -13%. The amplifier takes less than 240 VA.

The control's 12Vdc linear power supply is rated for 0.9A and is powered upon
application of AC into the unit.

ELECTRICAL AND ME CHANICAL SPECIFICATIONS

DOC/FCC (NTSC)

Power Output: ................................................................Visual 30 W peak, Aural 3W

Diplexing: ........................................................................internal, 10:1 V to A

Frequency Range: ........................................................54-216 MHz (channels 2 thru 13)

Amplifier Output Impedance: ....................................................................... 50 Ù

Output Connector: ................................................................................type N

Amplifier Input Impedance : ....................................................................... 50 Ù

Output Regulation: .............................................................3% (black-white picture)

Output Variation: .....................................................................2% (over 1 frame)

Amplitude/Frequency Response

-0.75 MHz to +4.75 MHz (Relative to Visual Carrier).........................................+0.5/-1.0 dB

Harmonic Radiation: ..............................................................................-60 dB

Spurious Emission (fv-4.5MHz, fv+9.0 MHz): .......................................................-50 dB

Intermodulation Distortion (3-Tone Method): .......................................................-52 dB

ELECTRICAL AND MECHANICAL SPECIFICATIONS

ELECTRICAL

AC Line Input: ..................................................................................120 VAC

Power Consumption (amplifier alone):

Black Picture and aural on (typical): ....................................................230 VA

ENVIRONMENTAL

Ambient Temperature: ........................................................................ 0° to +45°C

Humidity: .....................................................................................0% to 90%

Altitude: ...................................................................................... 7500 ft.

COOLING

Cooling air enters through the front panel perforations from the room, and passes into the amplifier
heatsink. The rear of this heatsink is fitted with a 4" fan that extracts the warmed air and exhausts it
back into the room. Other parts of the amplifier are convection cooled.

DIMENSIONS

Amplifier and exciter/translator chassis are standard 19" rack width;
Amplifier depth is 19" including a 3" allowance for connectors.
Amplifier height is 5¼" (3U).

The MX30V series amplifier is marketed on the assumption that the customer prefers to provide the cabinet or
enclosure for it.

VHF AMPLIFIER CHASSIS

Contents:

Part Topic Page

1 Chassis Description...........................................30-1

List of Figures:

Fig Title Drawing Reference

1 Chassis Assembly Diagram.............................40D2232 sht 1

2 Wiring Diagram, Amplifier, AC Line to Neutral........30C1987 sht 1

3 `power-one' Power Supply Data.....................................

1. Amplifier Chassis Assembly 40D22328G1 through 40D2232G3: Figure 1.

The Amplifier Chassis consists of a standard 19" rack mounted 5¼" 3U enclosure
containing 2 linear power supplies, the amplifier heatsink assembly, the output
directional coupler, the bandpass filter (in most models), a cooling fan, a
control panel (meter and control board), an RF metering board, a line filter, and
an AC relay. Its basic part number is 40D2232 .

Three frequency ranges are required to cover the entire VHF television s pectrum,
thus there are three fundamental models of RF amplifier assemblies: for channels
2, 3, 4; channels 5, 6; and channels 7 - 13.

AC power input for the three Amplifier/ models is connected for system operation
from one line to neutral, most commonly from 115 volts AC single phase.

40D2232G1 is the chassis for a 30 watt amplifier for operation on channels 7

through 13 (174-216 MHz), it has a 150 watt power supply, and its AC
is connected line to neutral.

40D2232G2 is the chassis for a 30 watt Amplifier for operation on channels 2,

3, and 4 (54-72 MHz), it has a 150 watt power supply, and its AC is
connected line to neutral.

40D2232G3 is the chassis for a 30 watt Amplifier for operation on channels 5

and 6 (76-88 MHz), it has a 150 watt power supp ly, and its AC is
connected line to neutral.

Although we indicate NTSC frequency ranges, the amplifiers are capable of
frequency coverage outside the ranges cited, for CCIR systems B, D, etc.
transmitter applications in other regions worldwide.

Figure 1 is the fundamental assembly drawing of the chassis.

The heatsink cooling fan is a 48 volt DC "Muffin" model from Comair -Rotron; it is

PUB98-30 rev 0: Dec. 12, 1998

30-1

30W VHF Amplifier

Comment:

must be altered to agree with
the revision date.

The footer date stamp

VHF AMPLIFIER CHASSIS

powered from the 48 volt amplifier power supply. As built, the cooling fan pulls
warmed air from the heatsink so the cooling air enters through the perforations
in the chassis front panel. This may be more convenient for a desktop cabinet
arrangement, but for cabinet racks fitted with ventilation filtering, the fan can
be mechanically reversed end for end, and remounted so that the fan forces air
through the heatsink, from which the warmed air exhaust leaves the chassis
through the front panel perforations.

A thermostat is mounted on the heatsink where operating temperature can be
sampled. If this temperature should increase past the trip point of the
thermostat,which is 60°C, its contacts will open and break the interlocking
circuit of the amplifier. The interlock circuit ultimately controls the power
supply to the amplifier, and the power supply will therefore shut down and remain
shut down until the heatsink cools and the contacts close again.

The chassis is wired according to one of the wiring diagram shown on Figures 2.

Chassis parts lists are provided on the last pages of this manual. The circled
numbers on the assembly drawing correspond to the "symbol" item numbers on the
parts list.

40D2168Gx means that the assembly can be any one of the 3 listed above, where "x"
denotes the group.

PUB98-30 rev 0: Dec. 12, 1998

30-2

30W VHF Amplifier

he footer date stamp

Contents:

Sec Topic Page

1 HB Helical Resonator Bandpass Filter Description (50W HB only)31-1

2 HB Low Power Bandpass Filter Description......................31-3

3 LB Low Pass & Notch Filter Description........................31-4

4 RF Directional Coupler Description............................31-5

List of Figures:

Fig Title Drawing Reference

1 Bandpass Filter response...........................text, page 31-2

2 Bandpass Filter schematic..........................text, page 31-3

3 RF Directional Coupler schematic....................text, page 8-6

4 Generic Helical Resonator Bandpass Filter Assembly ...30C1064 sht 2

5 High Band Bandpass Filter Assembly....................20B704 sht 1

High Band Bandpass Filter Schematic...................10A769 sht 1

6 Low Band Bandpass & Notch Filter Assembly............20B1118 sht 1

Low Band Bandpass & Notch Filter Component locations .20B1120 sht 1

7 Low Band Bandpass & Notch Filt er Schematic...........20B1151 sht 1

8 RF Directional Coupler Assembly.......................20B534 sht 4

Low Band Coupler PC Board Assembly ...................10A1942 sht 1

1. 30C1064G1 Helical Resonator Bandpass Filter (used with 50 watt High
Band):

The helical resonator was developed during the late 1950's and first described in
"Proceedings of the IRE" magazine by W. W. McAlpine and R. O. Schildknecht,

"Coaxial Resonators with Helical Inner Conductor," Proceedings of the IRE, vol.
47, no. 12, pp. 2099-2105; December, 1959. The same authors later published
another magazine article "Helical Resonator Design Chart," Electronics, p. 140;
12 August 1960.

IRE stood for the "Institute of Radio Engineers" which was responsible for some
of the television transmission standards that remain in use today. IRE later
merged with the "American Institute of Electrical Engineers" to become the
"Institute of Electrical and Electronic Engineers" which is known to us as the
"I-triple-E" and which continues publication of important electrical and
electronic engineering research papers in the "Proceedings of the IEEE" and in
the "IEEE Transactions" dealing with electrical and electronics interests.

We generally avoid such papers in our manuals except for the rare instance where
critical information is involved, as the content of most of these publications
are considered to be excessively arcane and esoteric for the beleaguered
technician whose sole interest is to get the transmitter back on the air. Should
you wish further information, we refer you to the above cited publications, to
"Reference Data for Radio Engineers, sixth edition" published by Howard W. Sams &
Co., and to the "ARRL Radio Amateur's Handbook" published annually by the

Comment:

is frozen. Any later
revisions made after the
initial release must have the
footer date agree with the
revision date.

T

1. Bandpass Filter: (continued).

LARCAN bandpass filter implementations generally consist of a cascaded series of
coupled resonators. Some use helical resonators; essentially a self supporting
high Q coil (the helix) mounted inside a metallic shield enclosure. One end of
the coil is solidly connected to the shield enclosure and the other end is open
circuited except for a small trimmer capacitance to ground. The dimensions of
the coil are critical to the frequency of operation; the assembly behaves as
though it were a quarter wave coaxial transmission line resonator. Several sizes
of coils and enclosures are necessary to cover the desired frequency ranges.

Fold-out Figure 4 indicates the generic assembly of a coupled helical resonator
bandpass filter.
The referenced drawing in Figure 4 happens to be a low band filter, but the high
band unit is laid out identically and appears almost the same as Figure 4 except
the high band helixes have fewer turns of coarser winding pitch, and their shield
enclosure dimensions are somewhat smaller.

The desired response shape is presented as Figure 1 below, and the filter
electrical equivalents are presented on the next page as Figure 2. When we
examine the assembly, and take capacitances into account, the equivalent circuit
of a helical resonator becomes simply a parallel resonant LC tank circuit having
low (trimmer) capacitance and relatively high inductance. Adjustment of the
trimmer produces a change of capacitance, and the trimmer's moveable slug is
shaped to appear as a shorted turn, which alters the inductance of the helix.

Matching from and to 50 ohm transmission lines is accomplished with taps on the
input and output helixes.

Coupling between sections is electrically a bridged T network of capacitors, and
is made up of the small capacitance between the free ends of the coils,
controllable by the amount of capacitance to ground that is introduced by the
coupling adjustment screws; the coupling is maximum when the screws are backed
out fully from the enclosure. Shielding partitions placed inside the enclosure
between helixes, produce fixed area apertures which affect the coupling
capacitance between helixes. Helix #3 in the Figure 4 drawing has taller
partitions on both sides of it, giving lower capacitance and less coupling than
the others.

For system use, the tuning and coupling is adjusted for a flat topped response
with steep sides, and the desired shape is such that fV - 4.5 MHz and
fV + 9.0 MHz are both 30 dB down, but the carriers must be fV < 0.6 dB and
fA < 0.7 dB departure from flatness. Input and output return loss must be 20 dB
or better over the full 6 MHz bandwidth. These idyllic sweep curves are shown
below as Figure 1.

This is the electrical equivalent of a series of five coupled helical resonators.
Similar lower power filters are built using conventional air wound coils and
ceramic trimmer capacitors, and these will be described next:

2. 20B704G1 Low Power Bandpass Filter for High Band:

Please refer to Figure 5. The configuration of this filter is similar to the
previously described helical resonator type in that it uses five LC resonant
circuits, but it differs in that two of these resonant circuits behave as high Q
traps for frequencies outside the band edge (_4.5 and +9 MHz), so that the
overall response has a reasonably flat top and steep sides. Factory adjustment
is made to achieve the same in-band response (carriers must be fV < 0.6 dB and
fA < 0.7 dB departure from flatness) as described for the helical resonator
filter. (We would have preferred to use this 20B704G1 filter for the 50 watt
high band system as well, except that the ceramic trimmers overheated due to the
higher RF currents at the 50 watt level, so the decision was made to go with the
higher power helical resonator filter for 50 watt high band transmitters).

Like the helical resonator filter, there are nine screw adjustments and two I/O
matching (with soldering iron) adjustments that need to be made simultaneously,
and all of them are interactive. Accurate adjustment is impossible without the
aid of a network analyzer, and because of the expense of this gear it is not as
likely to be available in the field; for this reason we say the filter is not
user-adjustable.

Sure, it is possible to use a sweep generator and detector for setting the
response of either filter, but unless an accurate 50 ohm return loss bridge is

used with the sweep generator, there is no way to properly set up the input and
output matching. Our recommendation: don't mess with the filter adjustments at
all.