Yep that ye old resistor/capacitor
Harold Lanfear said:
Does anybody have a wiring diagram to build a selector switch to add a second com radio? Another option would be to buy a simple audio selector switch, but they all seem to contain multiple function that I don't need.
I already have nice PS Engineering Stereo Intercom and would like to add a backup com radio without having to replace the existing intercom.
Thanks in advance to any responders.
To add to Jamies suggestion sometime a small non-polarized capacitor, probably 2.2 or 3.3 uF (faraday's) is nice to isolate the two audio signals. 2.2 uF probably will do. You can use the capacitors in series with the resistors. Play with the R and C sizes to get good balance. Than you would need a switch to select which one to PPT.
Some radios have an AUX AUDIO input or usually several AUX inputs. The Garmin VHF Com's do NOT have Aux inputs, but the ICOM A200 does. If you have one radio with Aux audio inputs, route the audio from one radio thru the one with the audio input. You don't need resistors or capacitors if you do it this way and you can listen to both radios if you like. If not you can use the capacitor/resistor deal and tie them together.
Use the volumn controls on each radio to select the audio to listen to or not. You can listen to both if you like. The switch method that was mentioned with the 4 pole switch works but, but than you can only hear one radio at a time.
The above suggestion of using a Double throw switch with an OFF postion is fine, but you can give yourself "radio failure" if the switch is selected to the center off position accidental. I can't think of a great reason why you would want to turn the both mic / ptt inputs off (disconnect). There may be a good reason I can't think of, but its probably he could only get a 4 pole switch in a double throw type.
Tie the audio together
radio #1 audio------R----C------\
.............................................|-----------> to intercom
radio #2 audio------R----C------/
Switch for PTT and MIC
...................................To intercom mic
.............................................^
.............................................|
radio #1 mic----> double pole single throw switch <-----radio #2 mic
radio #1 ptt----> double pole single throw switch <-----radio #2 ptt
.............................................|
.............................................V
...................................To intercom ptt
* You can't parallel the mics and ptt of each radio together, they must be switched.
Good luck