James,
I recommend you feed each radio output to your intercom via your switch
panel - each output in series with a 600 ohm resistor 1/4 watt - the input
impedance of the intercom is nominally 600 ohm - so you should mix the
signals without risk. If you find the volume too low, reduce the resistor
values to whatever the radio handbook recommends as a minimum load
impedance - be careful to select the correct wattage.
If you don't have an intercom you really need some form of buffer amplifier
to feed the loudspeaker or phones - or I remember Bob Nuckolls produced a
"Roll your own" intercom circuit.
Roger Mills
C/N 141
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> From: James Naylor <jnaylor@avnet.co.uk>
> Subject: Audio mixer
> Date: 12 October 1998 08:51
>
> A question for the radio experts out there.---
>
> 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.
>
> I'm sure there must be a simple design that could be built into a small
box
> with just one switch for selecting the radio (I have got this far) and
one
> to select the speaker for both or individual.
>
> Any help would be appreciated.
>
> Jim Naylor
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