| 300W VHF Power
Amplifier (CLASS-AB) |
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| Model No.: TW/VHFPA/300W |
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TWIN 100W VHFTV Transmitter based on LD MOS
technology is designed to meet the high
performance standards required for color TV
Broadcasting applications over Band IV & Band V
channel frequencies..
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| The power Amplifier
Consists of: |
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ALC PH ADJ BOX
ALC Box gets RF from changeover unit and
controls the amplitude of the RF to
compensate for level variation arising in
PA’s other stages. Thus keeping output level
constant.
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| PRE-AMPLIFIER (BGY-88): |
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AMPLIFIER PALLET
Driver Amplifier is 15W VHF Linear Class-A
having a gain of 31dB. +7dBm signal
(maximum) is fed to this amplifier and 6W
(nominal) is drawn to provide input to final
amplifier to get 300W sync peak output
power. The current of this amplifier is 3.5A
with +28V supply voltage.
AMPLIFIER PALLET
This amplifier is Class AB and incorporates
micro strip technology and push-pull MOSFET
to enhance ruggedness and reliability. This
Amplifier provides 300W sync peak output
power.
MONITOR BOARD
This board monitors parameters like forward
power, reflected power, temperature and
either indicate through meter/ LED or takes
action like level control and shutting of
the PA supply.
FILTER BOARD
These boards isolate supplies of
Class-AB pellets and Class-A Driver by coils
and capacitors keeping in view the high gain
of total PA. They also have provision to
measure accurately the current consumed by
each of the stages.
DIRECTIONAL COUPLER.
This coupler is used for sensing output
power of PA and is given to detect the
levels of Forward and Reflected power in
Monitor Board. The distinct feature is that
it has got repeatability built in the
design. It has coupling of 32dB to 34dB in
VHF Band.
ANALOG MONITORING
A small card is placed at the rear side
of the 300W power amplifier module for
proper DC voltage amplification of FWD PWR
and RFL PWR. These DC voltages have been fed
to Remote Terminal Unit (Refer Manual REMOTE
CONTROL SYSTEM) for PC monitoring of the FWD
and RFL PWR of the amplifier sub-system.
COMBINER
This combiner is 3dB, 90º-hybrid coupler. It
has got low loss and better phase balance.
500W sync peak RF outputs from PA-1 and PA-2
are combined in this combiner assembly. |
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| Product Test Specification
are as follows |
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| 1 |
ISO Port |
-24dB |
| 2 |
Phase difference between 0º and 90º |
90º ± 1º |
| 3 |
Level at 0º and 90º |
3dB ± 0.15 |
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Return Loss at 0º and 90º |
-26dB or better |
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| Specification are as
follows |
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| No. |
DESCRIPTION |
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SPECIFICATIONS |
| 1 |
Frequency Range |
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174 – 230 MHz |
| 2 |
Power Gain (Min) |
: |
56dB |
| 3 |
Power Output |
: |
300WATT (Peak to Sync at 1% SYNC Compression) |
| 4 |
Frequency Response |
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±0.2 dB in any band III channel |
| 5 |
IMD |
: |
Better than 48 dB |
| 6 |
Harmonics |
: |
< -60 dBc |
| 7 |
Spurious |
: |
< -55 dBc |
| 8 |
VSWR Trip |
: |
10W Black |
| 9 |
Input Return Loss |
: |
>16dB |
| 10 |
DC Input (Black Burst)
(At rated output power) |
: |
28V / 22A |
| 11 |
Indications |
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PA OK LED
GREEN |
: |
When PWR OK |
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FWD HIGH LED, RED |
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When FWD PWR Exceeds 320W (SYNC PEAK) |
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RFL HIGH LED, RED |
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When RFL PWR Exceeds 12.5W (SYNC PEAK) |
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TEMP HIGH, RED |
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When Thermistor Temp Exceeds 75°C |
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HEALTH |
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TTL High When PA Fails |
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TTL Low When PA OK |
| 12 |
Metering Indication |
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FWD |
: |
Indication in Green Range for PWR O/P 300W |
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RFL |
: |
Indication in Red Range for RFL PWR >10W |
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