On Mon, Mar 24, 2003 at 11:40:19AM -0500, Mark S. Adams, P.E. wrote:
>
> I figure that there would be room for switching for at least 8
> transverters, the board, and another switch that would provide a bypass to
> HF. To make this more clear, I figure that 50-432 bands would use a 28MHz
> IF and not go through the DEMI board, whereas 903-10G would use the board.
> As for 144, the DEMI board could be switched to an amp for that band. Since
> the signals in the box would all be 28 or 144 MHz nothing too exotic should
> be required.
You may already know this but something that you really
need to think about is that you will need a large amount
of isolation on the switching side of the transverters.
Typically the transverters are always on - so if you just switch
the 28mhz IF line around it is possible to get feed through.
On the VHF bands it would be quite easy to be listening to
the wrong bands signal and thinking it is just a weak
signal on the band you are switched to.
You could switch the DEMI transverters off when you change bands
but I think you will find the resulting drift on power up to
be quite annoying. DEMI provides an easy way to remove power from some of
the RX stages.
I recently built an IF switch that does this - on the RX side I used
a decent four position BNC relay to switch the IF lines and just
used one of the poles on some open frame relays for the TX IF side.
I also added a way to switch the transverters RX power on and off by
adding a small relay in each transverter. I control this relay
through one of the unused RCA jacks on the transverter - all I have
to do is short out the RCA jack to make the RX work in the DEMI unit.
This makes it very easy to use the units without the IF switch by
putting a shorted RCA plug in the jack to enable the RX power.
On the IF switch I have a pole of the relay that shorts those lines
to ground as you change bands. So far it seems to all work well
and I an hearing the other bands - even with strong local signals.
--
George Fremin III - K5TR
geoiii@kkn.net
http://www.kkn.net/~k5tr
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