[Moon] isolation relay performance

[Vladimír Petržílka]

Sorry for off topic: I haven't experience with such "white impurity" but
with anything else: when 50 terminator is used on the port of isolation
relay, the relay has always lower isolation compare use of short
connected (grounded) connector . Try to measure it. 
 
Just for info: We are using such old "home made relay" for TX port on
70cm: http://www.ok2kkw.com/rele1986.htm It is in the operation for
more, than 20 years.
 
The short connection of RX contact to ground is in our very old relay
design realized by silvered brass set screw. Such relay is OK up to
23cm, on 70 cm has almost 60dB isolation and in case of use 7/16
connectors it's usable up to 2 kW RF. When terminator was used for
grounding, isolation was aprox. 10 dB less. It is clear, because the
crosstalk to RX port is function of capacity between open RX port
contacts during TX ON. This crosstalk has quite high impedance, so as
low as possible impedance on RX contact grounding helps to improve
isolation.
 
Best regards
Vladimir
(I am not an EME operator, but HW support of OK1TEH operation only, hi)
 
-----Original Message-----
From: moon-bounces at moonbounce.info [mailto:moon-bounces at moonbounce.info]
On Behalf Of peter blair
Sent: Monday, February 18, 2008 11:26 PM
To: moonbounceboard; freetalk moonnet
Subject: [Moon] isolation relay performance



 This post is for general information and comment.
Between the receive port and the preamp on my 23cm feed I use an
isolation relay which switches the preamp between the feed (rx) and a
50R termination (tx) This is common practice and I do the same on all
the eme bands. I use small SMA type relays to minimise losses and
discontinuities. I recently had one that I'd used for probably 2 years
until it developed an intermittent loss of about 0.2-0.3dB showing
itself as a noticeable loss of moon noise or sun noise.  I changed the
relay and the problem went but this weekend I decided to take a look at
it as there seemed to be no obvious reason for it doing this. 
 The relay is an MA type ( 35x45x12mm) with  a nickel plated brass body
and the 3 SMA female sockets are screwed  into the top, each with a lock
nut. They look as though they are stainless steel.  I carefuly unscrewed
them and immediately noticed some white deposit in the threads. (I
should mention that the feed is only in the dish for a few days at a
time but the relay is not shielded from the weather) I cleaned up the
threads with a small wire brush ( for suede shoes!) reassembled the
relay and it is perfect again. The loss including 15mm 0.141 cable is
0.1dB measured on the PANFI as a change in NF. Repeated operation of the
relay has no ill effect. The gold plated contacts on the inner
conductors were nice and bright and clean
 I'm amazed that the water could penetrate the locknut and thread, but
it clearly did and the intermittency was presumably the mechanical shock
altering the corroded contact of the SMA outer. I shall in future shield
it from the wx but I thought it worthwhile to distribute this info as
its the sort of thing that can go un-noticed as a gradual degradation in
performance.
 I wonder if anyone else has experienced this?
 73 Peter G3LTF 
 
 

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