Increase handset audio

[AD0JA]

I am interfacing a motorola radius M100 RX and GM300 TX to an FF800 repeater controller. I am using the handset audio connection on the mic jack for RX audio, but the only problem is, the RX audio is very low, even if I put the RX pot at 99% on the controller. Does anyone have any ideas on how to increase the handset audio? And yes, I do have the handset enabled in the RSS.

Thanks
Jacob AD0JA

[Jim202]

There is a possibility that the connection FF800 is not DC isolated. I believe that you will find a DC bias voltage there. You can try using a coupling capacitor to block the DC voltage going to the FF800 and see if that helps. Something on the order of a 1.0 or a 2.0 uf capacitor should do the trick. Voltage is not that important as long as it is at least the battery voltage or slightly higher. Think a 15 volt rating will do you just fine.

Jim

[jackhackett]

According to the FF-800 manual the RXA - RXD audio inputs are DC isolated with a 1uF capacitor.

They say the min/max audio levels are 0.8/4.0 Vpp and they recommend around 2 Vpp.

I believe the Radius handset audio is not going to be enough. It's taken off of the 'volume control top' signal which the schematic shows as 300mV, and there's a 10K resistor in series so that's going to cut it down a bit more. If you've got a scope or meter that can measure that sort of AC level, you can verify the handset audio level.

If all of this is correct, you'd have to add some sort of amplifier circuit (could probably do it with a simple 1 transistor amp) or find a receive radio with a higher audio level available.