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Two Radios to One Intercom

 
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cluros(at)gmail.com
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PostPosted: Tue Mar 10, 2020 9:42 am    Post subject: Two Radios to One Intercom Reply with 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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ceengland7(at)gmail.com
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PostPosted: Tue Mar 10, 2020 10:48 am    Post subject: Two Radios to One Intercom Reply with quote

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: 1906
Location: Riley TWP Michigan

PostPosted: Tue Mar 10, 2020 11:19 am    Post subject: Re: Two Radios to One Intercom Reply with quote

Found this drawing someplace.

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PostPosted: Wed Mar 11, 2020 5:48 am    Post subject: Two Radios to One Intercom Reply with quote

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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Joe Gores




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