Question regarding audio output on the SLR5500

I received the following question via my contact form a few days ago:

I need to make a SLR5500 operate in digital mode but I want to add an analogue link using a  GM340. I managed to get PTT to work but I can't extract the audio from the repeater. According to the manual, audio should be on pin 3 (of the GM340) but this isn't working.

The SLR5500 does not produce audio on the accessory connector in digital mode. Only the SLR8000 is capable of this with a HKVN4368A licence.
The SLR5500 will present audio on the AUX connector but only when it is operating in analogue mode.

If you need to link MOTOTRBO repeaters using RF backhaul, may I suggest using MOTOTRBO Link.

If  you must use an analogue link or just want to bridge an analogue channel to digital, then you could trying using a DM1400 (or any other MOTOTRBO mobile) wired into the GM340 in a back-to-back configuration. The DM1400 would be monitoring a talkgroup on on one of the digital channels and the GM340 would be on your analogue channel. The two would be connected as follows.

Note that you might need to set the GM340 up to do flat audio as well as turn pre/de-emphasis off. The pin numbers are shown. The GPIO pin function need to be set in the CPS. The DM1400 should have AGC turned off.

You can use any (fixed) resistor value that is around 600Ω instead of the 470Ω shown. The potentiometer/resistor network is needed since RX audio is around 300mV and Mic audio is arou nd 80mV. The potentiometer lets you get the audio levels right and can either be a 10kΩ or a 22kΩ log/lin.

There are some limitations to what the above (back-to-back setup) can do. The audio on analogue will be no better than what 2,4kbps AMBE+2 sounds like. The important thing is not to overdrive the microphone input on either radio.

I've not tried this but you might want to add a series capacitor on the microphone input of both radios - 100nF should give you a nice -3dB/8ve rolloff. 

If you're going to be using a DM4000 series radio, you could try using one of the audio profile settings.