Garmin APOLLO GX SERIES, Service Manual

Page: 74 / 166

Garmin AT Rev --
7-36 GX Service Manual © 2004 Garmin AT
The following transmitter tests are not required for return to service. They are
included for troubleshooting. Continue on to the receiver tests below.
Modulation Audio Frequency Response
Step General Instruction Specific Instructions Expected Results
1 Set all test
equipment as
specified in Test
Equipment Setup on
page 7-17.
On HP8920, set AFGen1 to 20
mV.
2 Key the transmitter. On the test box, press the PTT
switch to TX.
3 Adjust audio level
input to obtain 85%
modulation ± 0.5%. Using the CURSOR CONTROL
knob or the
↑ arrows, adjust the
AFGen1 Lvl until 85% modulation
is viewed on the HP8920 (AM
Depth). NOTE: Always approach
the desired modulation from
lowest audio input level and stop
when desired modulation is
obtained. It may be necessary to
set INCR +divide10, or INCR SET
or INCR X10 to obtain a reading of
I=0.00100 for fine adjustment.
NOTE: Due to the 35-second time
out, the PTT switch may be
toggled from RX to TX to maintain
TX power during adjustment.
Confirm the AF Freq. meter
reads 1 kHz at 85 % modulation
± 0.5%.
4 Set AM Depth
measurement to
reference. On the HP8920, select the AM
Depth field. Then, select %. Press
the SHIFT (BLUE KEY) REF SET.
Push CURSOR CONTROL knob. The AM Depth field will read
0.00 ± 0.05 dB.
5 On the test box press the PTT
switch to RX.
6 NOTE: Option 019
required HP8920A. If Option 019 (the notch filter
option) is not installed, an external
variable notch filter will be
required to perform the following
test.
7 Lock notch and
audio generator. Use the SHIFT CONFIG keys
under SCREEN CONTROL. Use
the CURSOR CONTROL knob to
select the Notch Coupl. Set to
AFGen1. Push the PREV key
under SCREEN CONTROL to
return to TX TEST. Lock notch filter to AF Gen1
Freq. and return to TX TEST.