[VHFcontesting] DEM Transverters With Common IF Connection

[Zack Widup]

Hi Jim,

Depending on the relay used, there's no reason you can't use it as the
switching relay if it isn't passing more than a watt or so on
transmit.

All my transverters through 432 MHz use the circuit of "A
VHF/UHF/Microwave Transverter IF Switch" by Zack Lau, (at the time)
KH6CP, which was in August 1988 QEX. This circuit attenuates the
transmit RF before it gets to the relay. With 1.5 watts from an HF
rig, it supplies about -10 to +5 dBm output, which is adjustable. The
circuit works well through 144 MHz. If the DEMI transverter provides
attenuation of the transmit RF, you may have to modify it slightly to
bypass the attenuation on the transmit input. I've used this circuit
with my HTX-100 10-meter transceiver and my FT290RII 2m all-mode rig.

73, Zack W9SZ


On 12/15/12, Jimk8mr at aol.com <Jimk8mr at aol.com> wrote:
> Not precisely a contesting question, other than it concerns my VHF
> contesting station. But rather than subscribe to some other reflector for
> advice
> on one question, I'll pose it here.
>
> I recently replaced the TS-830S that had been the IF radio for my
> transverters  (222-432-1296) with a KX3. While I still also have a  HR-2510
> that I
> can use, clearly the KX3 would be a big improvement over  that. However, the
>
> KX3 won't provide the separate RX and TX IF inputs for the  DEM
> transverters.
>
> Has anyone had experience with modifying the DEM transverters for a common
>
> IF input/output?
>
> It appears that there is a unused half of the DPDT relay that switches  the
>
> DC between TX and RX. Does anybody know of any reason that could not be
> used  for switching the 28 MHz IF signal? Would 100 mw (or somewhat more) of
>
> 28MHz RF to the output of the RX chain  (i.e. if RF was applied without the
>
> relay switching, either with or without power on the last RX stage) be of
> concern?
>
> Any other issues to be concerned with?
>
>
>
> 73  -  Jim   K8MR
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