Garmin APOLLO GX SERIES, Service Manual

Page: 75 / 166

Garmin AT Rev --
© 2004 Garmin AT GX Service Manual 7-37
Step General Instruction Specific Instructions Expected Results
8 Change AF Freq. to
350 Hz. Using the CURSOR CONTROL
knob and the DATA keypad, set
AFGen1 Freq. to 0.350 kHz.
9 Key the transmitter. On the test box, press the PTT
switch to TX.
10 Read the difference. Read and record the AF Depth
difference.
The variation will be <4 dB at
85% modulation from 350 Hz to
2.5 kHz.
11 On the test box, press the PTT
switch to RX.
12 Repeat steps 9 to 12 for every 200
Hz until 2500 Hz is obtained. The variation will be ≤ 4 dB at
85% modulation from 350 Hz to
2.5 kHz.
Modulation Audio Frequency Distortion
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 ± 1%. 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
± 1%.
4 Read distortion. On the HP8920 set the AF Freq.
field to Distn. Record distortion. The distortion will be <10% at
85% modulation.