Re: TX-RX switching

Allison Parent <kb1gmx@...>

Hi Arv,

I used BJT as well, but used complmentary pair (PNP-NPN) so that
the transistors can both source and sink current. That solved the
ping (RX hangover) problem for me by actively grounding the contolled
circuits rather than letting them bleed down.

To further suppress any audio I added a 2n7000 mosfet in the audio
path to shunt it at the amp transistor on transmit.


--- In BITX20@..., Arv Evans K7HKL <arvevans@e...> wrote:


My BITX uses NPN's for switching. The 0.7 volt drop didn't seem to
bother much, but I am running 13.8 volts to the transceiver and 26 volts
to the IRF510 RF PA.

The problem with fast switching is that there are some bypass capacitors
in the receiver circuits that will keep the receiver alive for a few ms
after the transmitter comes on line. This causes a "ping" in the audio
system that can be quite loud. This is especially annoying when using
VOX to run QSK CW ( inserting a keyed tone into the microphone jack to
generate the CW ).


On Tue, 2005-11-08 at 21:59 +0000, ea4dsy wrote:

I am thinking of using a pair of P-channel Mosfets for swithching
and without voltage drop and relay coil power drain.


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