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[TowerTalk] Relays--summary

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Subject: [TowerTalk] Relays--summary
From: (Jim Reid)
Date: Fri, 25 Jul 1997 14:18:30 -1000
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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