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Two Radios to One Intercom

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cluros(at)gmail.com
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Posted: Tue Mar 10, 2020 9:42 am Post subject: Two Radios to One Intercom

Hello All,



I have been searching through the list archives as I'm sure we have discussed this before but cannot find the exact answer. We currently have a single VHF radio going to an intercom and would like to add a second radio. Input to the intercom would be controlled by the volume knobs on the radios and output will be controlled by a transmit select switch which will only allow the ptt line to be triggered on one radio at a time.

What is required to combine the audio output of the two radios to a single audio input on the intercom?

Thank you,

Sebastien

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ceengland7(at)gmail.com
Guest

Posted: Tue Mar 10, 2020 10:48 am Post subject: Two Radios to One Intercom

Simplest way is a ~500 ohm resister in series with each radio's output, and tying the downstream ends together to feed the intercom radio input.

 Charlie

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 On Mar 10, 2020, at 12:48 PM, Sebastien <cluros(at)gmail.com (cluros(at)gmail.com)> wrote: 	  Quote: 	
		   Hello All,



I have been searching through the list archives as I'm sure we have discussed this before but cannot find the exact answer. We currently have a single VHF radio going to an intercom and would like to add a second radio. Input to the intercom would be controlled by the volume knobs on the radios and output will be controlled by a transmit select switch which will only allow the ptt line to be triggered on one radio at a time.

What is required to combine the audio output of the two radios to a single audio input on the intercom?

Thank you,

Sebastien

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user9253

Joined: 28 Mar 2008
Posts: 1921
Location: Riley TWP Michigan

Posted: Tue Mar 10, 2020 11:19 am Post subject: Re: Two Radios to One Intercom

Found this drawing someplace.

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Joe Gores

roughleg(at)gmail.com
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Posted: Wed Mar 11, 2020 5:48 am Post subject: Two Radios to One Intercom

Here is an article on audio mixer circuits. The solutions presented in it involve use of an op-amp, which makes the circuit a little more complicated, but offers advantages in better gain and reduced crosstalk.

https://sound-au.com/articles/audio-mixing.htm 

I'm building a mixer for my plane to combine "aux" input (2-channel stereo music, to be mixed to mono) and the alert tone from my EMS into the aux input of my VHF COM radio. This is 3 inputs rather than the two you are looking at, but the principle is the same. Here's the diagram from the article that I plan on using.



[img]cid:ii_k7ndikza0[/img]



Hope this helps.

Pat



On Tue, Mar 10, 2020 at 1:29 PM user9253 <fransew(at)gmail.com (fransew(at)gmail.com)> wrote:



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 Found this drawing someplace.

 

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