Some interesting info here about how some of the commercial products are
built. Pretty sure I must be doing something wrong here though. Okay this is
just on the bench with a couple of pieces of coax and a couple of relays.
Relays are single pole 30A pcb mount type, encapsulated. Braid of the coax
cables joined together far ends of the coax go to sig gen and RX. Feed
enough signal to get S7 on the meter with the centres joined and then break
the centre of the 2 coaxes and connect to relay N/O contacts, braids still
joined. Increase sig gen to get S7 again. See a fairly typical 40dB at
14MHz. Add a second relay in series with the first with a wire between the
two not more than an inch long. Still see about the same isolation. Maybe I
need to move the relays further apart from each other.
Interesting on this one was playing with a K3 this week and noticed
something similar with the two antenna ports, S9 signal to the radio was
still audible when switched to the unused antenna port. I think they only
use a single relay in the antenna switching from Ant 1 to Ant 2.
Back to my switch project it seems clear that layout is critical as may be
the choice of relay to minimise coupling. Whilst I think I have a stray
coupling problem there also seems to be quite a few variables at play.
Martin, HS0ZED
p.s. This switch box is for my quad project, feeding the loops one at a
time.
-----Original Message-----
From: towertalk-bounces@contesting.com
[mailto:towertalk-bounces@contesting.com] On Behalf Of Martin Sole
Sent: 05 June 2010 12:21
To: 'Martin Sole'
Cc: TowerTalk@contesting.com
Subject: Re: [TowerTalk] Antenna switch isolation?
Thanks guys,
Just trying to stay sane, hi hi! Missed a 0 off though, 1kw would be 100mW
at the other connections but truly I think it can be discounted as said. Don
mentioned achieving 60dB, I'm not an expert at how to predict or determine
quite where the RF might go but I would be interested if there are pictures
of switches that can achieve better than the ~40dB that I can get,
appreciated my test was a bit 'dirty' .
Martin, HS0ZED
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