[TowerTalk] Relays for High Power

[Pete Smith]

At 07:21 AM 2/1/00 +0100, Bogomir Rejc wrote:
>
>
>> I am looking at some Potter Brumfield relays/switches to remotely switch
in 
>> loading at various antennas.  At a KW output, what should the rating of
the 
>> contacts be on the PB relays?  Will 5 amps be adequate?
>
>Voltage and current maximums on lossless lines are calculated 
>using  the following equations
>
>Emax=SQR(P*Zo*SWR)
>Imax=SQR(P/Zo*SWR)
>
>where SQR is square root, P power and Zo characteristic 
>impedanc.
>
>Assuming 1500W, 50Ohms and SWR=3 this would give 474V and 
>9.5A.
>
>Values calculated using the above equation are maximum 
>expected values. Losses in line tends to decrease these values. 
>
>So for legal output 5A under missmatch conditions wouldn't be 
>enough.
>
>Does anybody know how RF current ratings are related to usualy 
>specified 50/60Hz ratings?
>

Thanks, Mirko.  I asked a somewhat related question here recently and was
told by a number of people that 50/60 Hz ratings need to be discounted
severely for RF, depending on frequency.  No quantitative data though.
Maybe your query will elicit the info.

73, Pete Smith N4ZR
n4zr@contesting.com 

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