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Re: Preamp bypass circuit



Hello Hamish,

Please consider avoiding taking DC power from any radio connector.

In my scheme where I use an external sequencer and grab the MIC PTT
before it gets to the transceiver, I also need DC power for the mast
mounted preamplifier and legal limit SPDT coaxial relays, about 500 mA
total.
The sequencer switches the DC power to the mast mounted preamplifier
and relays.

Drawing more than a few mA of DC power from the radio is scary to me.
Manufacturer suggestions or specs are usually non existent, usually a
surface mounted transistor as a switch and not contact closure as in a
relay.

Stan, WA1ECF



Hamish Moffatt wrote:
> 
> On Wed, Feb 14, 2001 at 08:41:20PM -0600, Dave Metz wrote:
> > This is a one IC circuit so the construction is simple.  Yes, you will have
> > to go inside your 847 and reroute the PTT connection from the mic jack
> > to the rear apron of the radio to a connector and then route it back in
> > to the PTT circuit again.  You can also steal the power for the squencer
> > and the ground connection through the same connector.
> 
> Why not put the sequencer in line with the microphone, instead of modifying
> the radio? There is power available in the mic socket too.
> 
> Hamish
> --
> Hamish Moffatt VK3SB <hamish@debian.org> <hamish@cloud.net.au>
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