Adjusting The Receive Preamp - Mirage B-215-G User Manual

MIRAGE B-215-G
3. Next place a 3:1 mismatch dummy load at the output of the amplifier. The shut-down trip
point must be set to the most sensitive end of the band. The trip may be adjusted so the
circuit just trips at 140 to 152 watts. Adjust the trip by selecting proper diode as shown on
print as ZD3, and/or select the proper capacitance C25 across R24, the 62 ohm resistor
shown on the pick-up trace. A piece of 50 ohm coax, approximately 2 inches long, may be
substituted for C25 and cut to proper length to adjust the trip point. Remove the 3:1 dummy
load and reconnect the output coax.
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NOTE: C25 may be removed or temporarily disconnected to make the shutdown circuit
more sensitive.
4. Set SSB - FM switch to SSB. Key up and set SSB relay pot for 2 to 3 seconds of hang time
on the relay after it is unkeyed.

Adjusting The Receive Preamp

1. Remove the input and output coax cables for the amplifier radio and antenna connectors.
MAKE SURE YOU TURN THE TRANSMIT RADIO OFF.
2. Connect a coax from signal generator through a 5 dB pad to output connector on antenna
connector of amplifier. Set generator to mid-band 146 MHz with a -55dBm signal.
3. Connect a coax from spectrum analyzer to the radio input of amplifier.
4. Set spectrum analyzer to read 10dB per cm vertical deflection. Apply a 3cm reference signal
from generator (approximately -55dBm).
5. Turn on receive amplifier. Signal should increase 1.5 cm (15dB) with dip switch SW4 in LOW
gain position and 2.1 cm (21dB) in the HIGH gain position.
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NOTE: Because of the devices used, 12 dB gain is possibly all the gain that may be
achieved in a worst case event in the HIGH gain position.
6. If you do not have sufficient gain, adjust the variable capacitor C22 for 15 dB gain with S4 dip
switch in low gain position.
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