Parts List

2-6 VHF Enhanced Transmitter Instruction Manual VT-3 132 - 174 MHz
2.3.4 Deviation Setting
The transmitter maximum deviation range is set by jumpers at the factory to ± 5.0 kHz for the
VT-3 132 - 174 MHz transmitter. However, under some conditions such as a large change in
transmitter operating frequency, the deviation control may need adjustment. The transmitter
deviation is dependent on the operating frequency and this dependency is likely to be more severe at
the band edges. For frequency changes exceed ing ± 0.5 MHz, especially at the band edges, the
deviation should at least be checked and corrected if necessary. See the Audio Processor section of
the Transmitter Main Board Manual for details on setting the transmitter deviation. Note that the
adjustment of the balance compression levels, which is also discussed in the Audio Processor
alignment section, is not required as this adjustment should not be affected by a change in
frequency or deviation settings.
2.3.5 Setting RF Alarm Thresholds
The VSWR and Forward Power Alarms are factory preset to give alarm conditions for a 3:1
VSWR and 50 % forward power respectively. The Amplifier Manual describes how to adjust these
settings, should different levels be required. If the alarm thresholds are crital to operation of a
particular installation and if the transmitter undergos a large change in frequency (see section 2.3.2
above), the threshold alarm levels, particularly the VSWR alarm, should be checked.
2.4 Recommended Test Equipment List
Alignment of the transmitter requires the following test equipment or its equivalent.
Dual Power Supply: Regulated +9.5 Vdc at 2 A.
Regulated +13.8 Vdc at 2 A - Topward TPS-4000
Oscilloscope / Multimeter: Fluke 97 Scopemeter
Current Meter: Fluke 75 mult imeter
Radio communications test set : Marconi Instruments 2955R
VSWR 3:1 mismatch load: JFW 50T-035-3.0:1
Alignment Tool: Johanson 4192
It is recommended that the radio communications test set be frequency locked to an external
reference (WWVH, GPS, Loran C) so that the high stability oscillator may be accurately set to
within its ±1 ppm frequency tolerance.