Garmin APOLLO GX SERIES, Service Manual

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Garmin AT Rev --
© 2004 Garmin AT GX Service Manual 7-31
Receiver Dynamic Range
1. Inject a 1000 µV RF signal with 85% AM modulation at 1 kHz into the Comm antenna port.
2. Channel the Comm to the same frequency as the signal generator.
3. Connect a 4 ohm resistor and AC power meter (or voltmeter) across the speaker output.
4. Turn up the volume control on the Comm radio to make sure the output power can be greater
than 12 watts (6.93 Vrms volts across 4 ohms).
5. Open the Comm squelch by pulling the squelch knob out.
6. Measure SINAD on the speaker output with a 4 ohm load resistor.
7. Adjust the RF level of the signal generator until the SINAD reads 6 dB.
8. Increase the signal generator RF level +107 dB from the level necessary to obtain 6 dB
SINAD.
9. Measure audio distortion; it should not exceed 5%.
Dynamic range _____ OK
Weather Channel
1. Inject a 1000 µV RF signal with 3 kHz FM modulation on 162.4 MHz into the Comm antenna
port.
2. Channel the Comm to the same frequency as the signal generator.
3. Connect a 4 ohm resistor and AC power meter (or voltmeter) across the speaker output.
4. Turn up the volume control on the Comm radio to make sure the output power can be greater
than 12 watts (6.93 Vrms volts across 4 ohms).
5. Test squelch by pressing NRST to put the WTH into secondary channel.
Squelch test ______ OK (No audio when WTH is put into secondary channel)
6. Press MON button on the Comm radio
Monitor Test _____ OK (Pulsing 1 kHz tones present when MON button is pushed)
7. Measure the audio output with an ocilliscope with the MON button pressed.
Scan time _____ OK (20 mS blank time between the 1 kHz tone)
8. Press the INT/OFF switch to INT
Speaker audio _____ OFF
Headset audio _____ Pulsing 1 kHz tone present