Re: TX-RX switching

Arv Evans K7HKL <arvevans@...>
 

Allison

Your approach to the problem sounds better than mine.  I used the brute force method and put a relay in the speaker lead.

Arv
_._

On Wed, 2005-11-09 at 13:20 +0000, Allison Parent wrote:
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.

Allison
KB1GMX

--- In BITX20@..., Arv Evans K7HKL wrote:
>
> IEA4DSY
>
> 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 ).
>
> Arv K7HKL
>
> On Tue, 2005-11-08 at 21:59 +0000, ea4dsy wrote:
>
> > I am thinking of using a pair of P-channel Mosfets for swithching
> > fast
> > and without voltage drop and relay coil power drain.
> >
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