Re: Good place to tap for PTT-OUT #v5


Jerry Gaffke
 

Yes, the TX rail has 12v on it whenever the rig is transmitting, 0v when it is not.
Probably your best choice, and easy to tack a wire on it.

Does your amplifier really want a 12v signal, or something more like 5v?
How much current will the amplifier draw from this signal?

I would think about limiting the current somehow, perhaps a series resistor inside the uBitx.
Otherwise a miss-wire in the cable could cause 10 Amps to flow, and lots of smoke.

Jerry, KE7ER


On Tue, Mar 16, 2021 at 10:38 AM, Rob French (KC4UPR) wrote:

I'm looking to add a PTT-OUT to the back panel of my uBITX, to control e.g. an amplifier or a switch to isolate an external SDR during transmit.

My thought is to grab C154/D11 or one of the other filter-switching relay circuits.  Those look like easy places to tack a short wire to without having to completely disassembly my uBITX.

Two quick questions:
(1) Dumb question... but that junction does provide what I want, right?  i.e. +12V on transmit.
(2) Any downsides to tapping the +12V on transmit, from that location?  e.g. some RFI effect

Thanks,
Rob KC4UPR

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