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[TowerTalk] Relays--summary

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Subject: [TowerTalk] Relays--summary
From: (Healy, Rus)
Date: Thu, 31 Jul 1997 09:25:08 -0400
Certainly, for high-SWR situations, wider contact spacing is a good
thing. I was seeking a source of relays for switching in a 50-ohm system
(where the peak voltage never gets very high), which I didn't specify.

--73, Rus

>From:  Jim Reid[]
>Sent:  Friday, July 25, 1997 8:18 PM
>To:    Healy, Rus;
>Subject:       Re: [TowerTalk] Relays--summary
>At 10:30 AM 7/25/97 -0400, you wrote:
>>Thanks for the input on relays. Interestingly, I got more messages
>>asking for a summary than I did with actual input.
>>The overwhelming winner was the Radio Shack 275-218 DPDT, 12-V coil
>>relay with 10-A contacts, which sells for about $6.99. 
>Hi again,  Rus,
>But what about high swr situations?  I was afraid of the close
>contact spacing in  the RS relays.  When running 1.5kW to my
>V-beams,  can get some pretty high vswr in the feed system.
>For example, at a 3:1 vswr in my 450 ohm feedline,  and at
>1.5kW, the peak voltage is about 2000!  And rms voltage is
>1400+.  So I decided to go with bigger relay units  with
>good contact separation.  as I had no idea when a voltage
>might stand on the line at the relay position near the peak
>values.  Maximum rf current at the same conditions is
>only 3.2 amps in the 450 ohm setup.
>With 50 ohm coax,  the same vswr and power result in only
>670 volts peak,  but 9.5 amps of rf current.
>Anyway,  that's why I chose the bigger,  and more costly
>antenna system switching relays.
>73,  Jim, KH7M

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