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[TowerTalk] Relays

To: <>
Subject: [TowerTalk] Relays
From: (on4kj)
Date: Tue Feb 25 14:08:06 2003

Seen that problem 30 years ago on LF switching a few ?A of LF sigs from a
Our sollution,Let flow a couple of mA DC through the contacts at the same
time, using Cps to block DC elswhere then thez contacts.
What say.

----- Original Message -----
From: "Doug Faunt N6TQS +1-510-655-8604" <>
To: <>
Cc: <>
Sent: Tuesday, February 25, 2003 7:16 PM
Subject: Re: [TowerTalk] Relays

To: <>
>    Date: Tue, 25 Feb 2003 18:45:56 +0100
>    From: =?windows-1252?Q?Jir=28=ED_=8Aanda?= <>
>    Hi Mikael,
>    you have two problems:
>    1. - the smaller one - the relay should handle about 7-10A
>    2. - THE MUCH bigger one - the relay should also be capable of
>    transfering 0.3 microVolt/50 Ohm - i.e. 0.006 microA . If you start to
>    play with this you find that this is THE PROBLEM. Most of the switches
>    work fine while on TX but you might be deaf on RX without knowing  -
>    might have 10-30dB atenuation and how to find out, it might be easily
>    just the propagation. Just check up WX0B advice on all his gear. "Hot
>    switch time to time and the oxide on contacts and might burn out" !?!?
>    Definitely if the relay is open frame and is silver plated you are
>    to watch problems caused by oxidation thin noncoductive layer will
>    down while on TX so you will not observe any SWR deterioration , while
>    on RX it will be there and you will be listening just through the
>    capacity of the contacts and insulating layer ! You can expect the
>    layer to withtad up to hundreds of mV to couple of Volts than it
>     I have observed this phenomenon many many times and until we (me +
>    OK1RF) get of rid of most realys in the way. This phenomenon caused me
>    definitelvely a couple dozens of  decicive QSOs in various contest
>    during passed years.
> I looked at the relays that Force12 uses in the relay boxes for
> changing the center frequency of their 80M and 40M antennas.  They use
> a standard 30A 250V DPST power relay.  I got some from McMaster-Carr
> here in the US, which are exactly the same.  These relays have a
> wiping action on closure, which should help some, and F12 recommends
> turning the TX power to 10W and hot-switching them, periodically to
> clean them, but warns against hot-switching at full power.  I've not
> heard of any problems with them, but you can't really tell.
> 73, doug
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