For what it's worth, I now operate very easily with the station
optimised for both 73kHz and 136kHz with a fairly fast manual
changeover.
The connection from the antenna to the coil can be made either to
the 136kHz tap or the 73kHz tap (actually not a tap but the top of
two coils). This works fine for transmit on 73 and receive on 137. To
transmit on 137 I simply change the tap on my matching
transformer as the impedance on slighly different.
My changeover time is about 30 seconds - more than adequate for
two-way QRSs.
I find it important to optimise the antenna tuning on receive
because the Datong LF converter has a broadband front end and it
needs as much input selectivity as it can get.
Mike, G3XDV (IO91VT)
http://www.dennison.demon.co.uk/activity.htm
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