Daniels VT-3/140-SWA2, Instruction Manual

Page: 60 / 262

3-14 Transmitter Main Board Instruction Manual
3.11.4Tuning the Transmitter
For all MT-3 transmitters, apply a low impedance source of 20-300 Hz to the Direct Modulation
input of the transmitter (Pin Z28 of the 48 pin connector) through a 22 uF capacitor, positive
terminal connected to pin Z28. A Marconi 2955 works well for this test. Adjust R44 on the audio
processor to the fully clockwise position.
• Apply a 100 Hz tone at -8 dBm to the Direct Modulation input of the transmitter (Pin Z28
of the 48 pin connector, and key the transmitter. Adjust the level of the tone until a
deviation of 1.5 kHz is acheived. Note that the level required may be anwhere from -10
dBm to 0 dBm depending on the type of transmitter.
• Confirm that the frequency response rolls off by checking that the following deviations
are observed: (note that the deviation will NOT roll off at 300 Hz if an OC-3 crystal
oscillator is used instead of a synthesizer).
- 20 Hz tone gives about 700 Hz deviation
- 100 Hz tone gives 1.5 kHz deviation
- 300 Hz tone gives about 500 Hz deviation
• Finally, confirm subtone 1 modulation: set-up for 100 Hz Mod with 500 Hz Dev.
- Check 200 Hz Mod, Dev = 1.5 (VHF) / 2.0 kHz (UHF)
- Check 300 Hz Mod, Dev = 1.5 (VHF) / 4.0 kHz (UHF)