Doc,
I would bet that there is a mismatch along the jumper. I would vary the
length of the jumper and watch the swr. It should remain nearly the same if
the exciter and load impedance are matched.
Along with mismatch comes circulating currents. Since the currents may be
reactive and out of phase with the source voltage, we often say that they do
not result in heating. However the voltage drop due to the resistance of the
line is in phase with any current passing through it and therefore, it
causes heating. So yes, mismatch can result in temperature rise in the line.
I hope this is helpful in pointing you to the possible cause.
73, Jeff - K1LE
----- Original Message -----
From: "Doc Johnson" <bluescreen@comcast.net>
To: <amps@contesting.com>
Sent: Saturday, April 20, 2002 12:50 AM
Subject: [Amps] Warm Coax question
> I am not sure where to ask this question but it kinda fits in this forum.
I
> have a 2 meter repeater system. It consists of multiple RX feeding a
voting
> system then feeding a 375 watt Micor xmitter. The xmitter is located on
top
> of a building approx 60' away from the antenna (DB224 4 bay dipole) which
> is fed with 7/8" foam hardline. I am using a 2' jumper to connect the
> xmitter to the antenna which has been 9913 and rg213. The jumper gets
> quite warm to the point it is uncomfortable to touch. Another confusing
> issue is I tune the amp up with a Bird watt meter and when I remove the
> watt meter the plate current lowers by about 50-75 mills. Any input? SWR
> is 1.3.:1 which seems a touch high for an antenna that is tuned for the
> amateur band.
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