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.
>From: Jim Reid[SMTP:firstname.lastname@example.org]
>Sent: Friday, July 25, 1997 8:18 PM
>To: Healy, Rus; email@example.com
>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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