>I want to connect two radio's together so that I can switch to either for
>transmit and receive, with the option to receive on both. I know audio
>panels are available commercially, but they usually contain Markers ADF etc
>which I do not need, not to mention the cost.
>The only problem I have encountered, is feeding the two audio outputs into
>one speaker at the same time. Some form of isolation circuit is required
>to prevent the two radios trying to drive each other backwards, so to
>speak.
Are you really considering a "speaker"? Don't know many homebuilts
with sufficiently low cabin noise to allow comfortable use of speakers.
Here's something I've used on several simple systems (two receivers).
Use a 47 ohm, 1/2 watt resistor in series with EACH radio's headset
output to drive both headsets in paralle. This has the effect of cutting
output voltage from each receiver by 1/2 but it's generally made up
quite easily by turning up the volume. I genrally don't bother to put
switches in the headset lines from each radio and choose to control
each radio by setting its volume control.
Use a two-pole, two position switch to flip the microphone audio and
press-to-talk lines between the two transmitters. This is very easy
to implement and see how it works before you go out and buy/build
an isolation amplifier.
Bob . . .
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