# [TowerTalk] Relays for High Power

**Bogomir Rejc
**
bogomir.rejc@eta-cerkno.si

*Tue, 1 Feb 2000 07:21:22 +0100*

>* 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?
73s, Mirko, s59x
----------------------------------------
Bogomir Rejc, S59X
Platiseva 25
5282 Cerkno
SLOVENIA
AX.25: s59x@s50box.svn.eu
Email: bogomir.rejc@eta-cerkno.si
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