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December 16th 04, 07:07 PM

On 16 Dec 2004 10:26:06 -0500, (Scott Dorsey) wrote:

TW wrote:

Quoting from the Vectronics VEC-1220K 20M transmitter kit manual, page
26: "Receiver Hook-up: You may patch most receivers directly into your
VEC QRP-CW Transmitter's receiver jack without risk of damage.
Transmitter output is typically around + 32 dBm and the energy
reaching your receiver through the T/R switch is normally 25 dB lower,
or about +7 dBm. This is a very strong signal, but a high-quality
receiver with a wide AGC range can usually handle it without blasting
out the speaker! If you are able to leave the receiver on during
transmit, you'll enjoy the benefit of full QSK operation."

It would strike me that if you really wanted a full T/R switch, and you
did not want to spend the five dollars or so for a fast relay, you could
probably build an acceptable switch using 1N4007 diodes. I would think
that with these current levels at HF that there would be no need for a
fancy switching PIN diode.

Another alternative, by the way, is just to use a vertical for transmitting
and a horizontal dipole for receive. This also has some major benefits in that
your receiver noise will be lower with the horizontal and your transmitted
signal will be slightly better with the vertical.
--scott

Hi Scott,
The existing circuit simply uses one 1N4007 and a 1N4148 in series
thru a .01 cap to the receiver muting input (it is not THAT simple,
they are across the emitter and collector of the keying transistor; I
tried to draw it in text symbols, but gave up). What I hear in the
phones on keying is a loud "square wave" thump on each character sent.

I bought the Vectronics kits a couple of years ago after a period of
inactivity due to illness, mainly to get engaged and productive on
something.

I'll check out some designs in my 2000 and earlier Handbooks for relay
and/or diode switching better than the current Vectronics QSK design.
I can in fact use a vertical and a dipole, so that is a good
suggestion. Meanwhile, I enjoy QSK with my SW-20+.

Thanks,

Ted KX4OM

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