wb2vuf@qsl.net wrote:
> There is also a reed relay that switches the antenna input to the
> receiver. If you have the amplifier switching relay active, you don't
> hear the reed relay, but with the amp relay disabled, you will hear a
> gentle "ping" coming from the reed relay.
>
> Bob WB2VUF
... this reed-relay does not switch the antenna to the receiver, it only
disconnects the rf final from the antenna during receive. A pair of cheap
rectifier diodes type 1N4007, which indeed have the characteristics of
PIN diodes, form an electronic T/R switch that connects the antenna to
the receiver. By the way: Instead of using a fixed voltage, a sample of
the transmit signal is rectified and used to reverse-bias these diodes
in a very simple and clever fashion. This unique biasing scheme of the
PIN-diode T/R-switch grants secure isolation between transmitter and
receiver *independent* of SWR and transmit power. All in all, the QSK
of the Corsair II is one of the best that were ever realized.
73
Karl, DJ5IL
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