[TowerTalk] Relays for High Power

[Tod Olson-MN]

My recollection of the specifications catalog for the RF1D series of vacuum
relays was that the contacts were rated in terms of DC, AC (60 Hz) and RF at
say 1 MHz 10 MHz and 30 MHz. The 30 MHz ratings were ( as I recall) about
1/3 the 1 MHz ratings in term of current.  This lends some support to the
'Elmer rule of thumb' mentioned by John. His advice on 'don't do hot
switching' is something I will echo.

In about 1970 I put together a system that allowed me to have QSK using a
Collins S-Line with a Collins 30S-1. I would time delay the keying by a few
milliseconds to allow the relays to close and open (and bounce) with no RF
on the contacts. I used the RF1D relay. It has a rating of about 1 amp at 30
MHz. My spare RF1D's are still unused because this switching system worked
well (you do need to have a low SWR on the feedline).

Personally, I use vacuum relays for switching wire antenna elements. (I
prefer the kind that are latching). I never switch things with RF applied.
Voltages can get very large for some configurations and the vacuum relays
seem to handle high voltages without a problem. The cost of the vacuum
relays (at flea markets, etc.) is more, but not dramatically more than the
Radio Shack relays. Their capability is much more.

Tod, KØTO




----- Original Message -----
From: "John Langdon" <jlangdon@outer.net>
To: "alsopb" <alsopb@gloryroad.net>; "Pete Smith" <n4zr@contesting.com>;
<towertalk@contesting.com>
Sent: Tuesday, February 01, 2000 9:31 AM
Subject: RE: [TowerTalk] Relays for High Power



My "Elmer" W5GEL, taught me to "derate" by a factor of 3 for HF, i.e., if
the contacts are rated for 9A DC, do not plan exceed 3A of RF.  Strictly a
rule of thumb, and assumes no hot switching..

73 John N5CQ




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