Topband: RX/TX Antenna decoupling

[Guy Olinger K2AV]

The answer to a lot of these either/or station wiring quandaries on
RX/TX/RX transitions is a slow-relay assert-TX signal. This is a signal
that would properly drive the frame relay RX/TX/RX in an un-QSK'd AL1200.
This is available in any WinKey or WinKey based device like MicroHam. In
contest setups this is the box that creates clean keying from ascii streams
on USB lines from contest logging computers, and accepts key and paddle
input. The TX-assert to key-down and TX release after key up delays are
programmable and can be set to exactly fit a station requirement.

Particularly on 160/80 where many stations never operate without a RX
antenna active on a port on their receiver, slow-relay assert-TX signal can
drive a frame relay to disconnect/connect BOTH leads of feedline at the
antenna with precisely set assert and release delays around actual RF power
on line.

We run the transceiver in its QSK mode. All we will lose is the benefit of
best possible RX signal **between dits** from the TX antenna. We will still
hear RX antenna signals from RX antennas, even if somewhat diminished by
the still-connected TX antenna. But we will still know if someone is
transmitting on top of us.

This also allows us to disconnect an RX antenna, like an SAL30, from it's
control/amp circuitry, when it's too close to the TX antenna. We can use
slow-relay assert-TX to switch to an omni RX antenna for QSK, optimally
located away from the TX antenna and safe to keep on our RX during TX.

Lastly but not leastly, the slow-relay assert-TX signal allows us to cut
down on the relay cycles on pain-to-replace and often noisy vacuum relays
in expensive big tube amps that we would rather send elsewhere for repair.

73, Guy K2AV

On Thu, Oct 5, 2017 at 9:44 AM, Rob Atkinson <ranchorobbo at gmail.com> wrote:

> I discovered my rx antennas worked much better if my tx antenna was
> completely disconnected from the station.  Most coaxial relays or T/R
> switches only break the center conductor.   That's not good enough.
> There has to be a complete disconnection which I provided by using an
> open frame relay mounted in a plastic box.  On 160 m. such a device
> will not present an impedance bump but this solution worked for me
> because I don't care about QSK.  This may not be necessary if the tx
> and rx antennas can be separated by one or more wavelengths.
>
> 73
>
> Rob
> K5UJ
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