Garmin AT
Rev --
© 2004 Garmin AT
GX Service Manual
7-45
Reference Sensitivity and Squelch Threshold Sensitivity
Step
General Instruction
Specific Instructions
Expected Results
1 Set
all
test
equipment as
specified in Test
Equipment Setup on
page 7-17.
2
Sig. Gen. Mod Lvl.
To 30%.
Amplitude to 1000
µV.
On the HP8920:
1. Set AFGen1 to AM 30%.
2. Set AMPLITUDE to 1000
µV.
3. Set Ext. Load R 4 ohms.
3
Move test cable.
On the test box, connect the
HP8920 audio in cable to SPKR
OUT.
4 Adjust
volume
control on Comm
radio for 12 W.
On the Comm radio, adjust the
volume control until the AC Level
reads 12 watts.
≥
12 watts output into 4 ohm
load (mounted in test fixture) at
a volume level from 0 to 12
watts.
5
Open squelch.
On the Comm radio, pull the
Squelch knob out (disable
squelch).
6
Get 6 dB SINAD
reading and record
reference sensitivity.
On the HP8920:
1. Set the value field in the
SINAD meter reading to
average (AVG) at 10.
2. Set AMPLITUDE using the
↓
down arrow until the SINAD
meter reads 6 dB SINAD.
3. Record AMPLITUDE as
reference sensitivity.
4. The volume on the HP8920
can be adjusted to monitor
the Comm radio audio.
<2 µV (hard) for 6 dB S+N/N
with 30% modulation at 1000
Hz modulation.
7
Close squelch.
On the Comm radio push the
Squelch knob in (close squelch).
The Comm radio will have no
audio out.
8 Get
squelch
sensitivity.
On the HP8920:
1. Set AMPLITUDE using the
↑
up arrow until the SINAD
meter reads squelch opens.
2. Record AMPLITUDE as
squelch sensitivity threshold.
Will start to break at greater
than:
2 µV (-104 dBm).
Note: Will be full open if signal
is increased by 3 dB.
Summary of Contents for APOLLO GX SERIES
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