[App_rpt-users] Using a handmic while using a URI

[Jeff DePolo]

> Well, I need the radio to be able to use the microphone. I 
> know that it is not the easy solution but it is the one that 
> I am going for. I do not want to open up the radio so I am 
> going to try and design a circuit so that the mic and the URI 
> can be connected into the microphone jack. I will also 
> include some digital logic so that if both the URI and the 
> mic a trying to key up, then only the signal from the mic 
> will go through. I will try and upload a schematic later. 

You didn't say what kind of radio it is (or if you did, I didn't see it).
The best and/or easiest way to implement this is going to vary with the type
of radio.  

At the very worst, you need is a SPDT switch (CD4053 appropriately biased,
reed relay, whatever) and a couple of steering diodes.

But depending on the radio, it could be as simple as hard-OR'ing the PTT's
together and resistively summing the audio.  You likely have way more audio
output available from the URI than you'll need to drive the mic input, so
there's a good chance all you need to do is add enough series R in the audio
coming from the URI to prevent loading the hand mic.  Assuming you're using
the AC-coupled output from the URI you don't even have to worry about
DC-blocking the mic bias.

					--- Jeff WN3A


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