Audio Selector Question

[Harold Lanfear]

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.

[Jamie]

Hi Harold:

You can probably get away with just passively mixing the audio outputs of the two COMs together into the audio input of your intercom, then just put the mic and PTT lines on a toggle switch to let you select which COM you're transmitting on. Doing it this way will let you monitor one COM while you're transmitting on the other. If you don't want to hear the second radio, just turn the volume down. One caveat to using this approach is if both radios are on the same frequency it's going to get very noisy when you transmit. :-)

When you mix the audio you'll need to throw some resistors in there. Just use trial and error with the resistor size until you have something that sounds right.

I passively mixed my audio sources. I have the Dynon EMS that I wanted to mix with my COM into my DRE 244e intercom. I crimped various resistors to d-sub pins, then soldered the other ends of the resisters to a single wire:


Sorry...I didn't get a picture with the d-sub shell removed.

In the future if I need to add another audio source I can simply add another wire to the d-sub connector that mates to this one.

Alternatively, Stein sells a switch (see here, part #SA-818) that will let you switch everything between the two radios.

Hope that helps,

[gmcjetpilot]

Originally Posted by Harold Lanfear

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

[RV6_flyer]

Originally Posted by Jamie

When you mix the audio you'll need to throw some resisters in there. Just use trial and error with the resister size until you have something that sounds right.

For the past 1,000 flying hours, I have mixed a GX60 and SL30 together using 100 ohm resistors with no issues. NO capacitor. DPDT switch to switch between comm 1 and comm 2.