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[AMPS] Antenna System Power Ratings Question

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Subject: [AMPS] Antenna System Power Ratings Question
From: jreid@aloha.net (Jim Reid)
Date: Mon, 19 Oct 1998 12:12:14 -1000
Aloha Big Gun HF amp users,

At what power levels do you have to start worrying about
antenna system components?  All our "stuff": PL259's, N's,
9913,  LMR-400,  typical commercial antennas,  switches,
even the Top Ten devices remote switches,  etc.  are all
fine up to and somewhere above the 1500 watt CW,
RTTY continuous output level.  Some antenna tuners
are rated to 3kW;  at least one soon to be for sale,
the Ameritron ATR-30 will handle a real 3 kW,  or
at least so I am told.  I suppose it will have S)239 sockets,
so maybe they are good to at least that power level.

Any comments on the topic?   Up to what powers will
the usual componentry live,  and at what power do you
have to start upgrading to large hardline,  perhaps
home brew antennas,  tuners,  etc?

I calculate that at 3 kW,  for example,  in a 50
ohm system, with say 2:1 vswr, the RMS voltage
will be 548 volts;  peak voltage, 1.414 times that,
or at  775 volts,  and the RF current will be about
11 amps.

Typical good RG8 size coax is rated at 4000 or 5000
volts breakdown,  and yes, as the vswr increases,  this
rating drops,   so also the power handling capacity.

In a balance feed/antenna system,  using, say 450 ohm
twin line,  and still 2:1 vswr (band edges,  say), the voltage
increases to an RMS of 1640 volts,  and peak of 2325 volts,
and the current,  of course drops to about 3.6 amps.

Amidon High Power baluns still use the SO239 socket
on units rated at 10 kW,  I believe.

It would seem the lowest lost system would be the twin line
feed and balanced tuner,  a la,  old Johnson AM kW Matchbox. 

Just curious,

73,  Jim,  KH7M
On the Garden Island of Kauai


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