Recording both TX and RX audio from CDM

[hobbes]

I'd like to be able to set up a base CDM1550 so that I can record both RX audio (easy enough from the rear accessory connector) AND be able to record TRANSMITTED audio from the local desk mic -- that is, record both sides of the radio traffic. Any thoughts on how to accomplish this?

Does TX audio get repeated out at the accessory connector somewhere? Or could I put something inline (like a 1:1 audio isolation transformer) between the mic and the control head and capture audio that way?

Any suggestions are welcome!

Thanks!

[Bill_G]

Simplex or repeater channel? If it's simplex (tx=rx), then put up another mobile monitoring that freq to record both sides off the rx. If it's a repeater channel (tx does not equal rx), and you have a scanning mobile, you could try the same trick hoping it will lock on the correct side each time quickly enough to capture all transmissions. Otherwise, you need to find, or make, a summing amp with two lines in and a single line out to capture, and isolate, the mic hi and rx hi out of the CDM. You could try using resistors and caps off each side forming a bridge with a single output that might knock the levels down enough to prevent cross talk but still be high enough to record. You would have to experiment with values.

[RFguy]

We typically use a mixer amp to mix the 2 audio sources (RX and TX audio) to feed to the recorder. I prefer ones with adjustments to allow for balancing of the audio.

This is one we have used in the past:
http://www.omnicronelectronics.com/digital/rsa-u5.htm

[hobbes]

The Omnicron device seems to be what I'm looking for. Thanks!