Adrian,
Power factor is a quantity associated with mains power (and similar
power distribution systems). In the old days (when I went through EE),
it was, indeed, related to the phase angle.
With RF systems, it's the load that the antenna presents to the
feedline, and it's different at every frequency. It's primary
significance is how it looks to the feedline, which in turn affects loss
in the line and, after being transformed by the line, whether the
transmitter can put power into it. The function of an antenna tuner is
to transform whatever that impedance is to something the 1) makes the
output stage "happy", and 2) that the output stage can supply power to
without stress on the output stage that could cause destructive failure.
When "happy" has been achieved, the transmitter is delivering power to
the line, but if the match between antenna and line is poor, not much of
that power may get to the antenna, but be turned into heat in the
transmission line.
Remember I said that VSWR in a system is set by the load (the antenna)
and is decreased by the loss in the line. If the line is long enough and
mismatch is great enough, the VSWR eventually ends up a 1:1. I've used
this example as an extreme case: a 1,000 ft spool of RG58 with a 10K ohm
load would look like a perfect 50 ohm load to a transmitter at 28 MHz,
the SWR would read 1:1 at the transmitter end of the line, and loss in
the feedline would be huge.
73, Jim K9YC
On 3/4/2020 9:57 PM, Adrian wrote:
Jim, yes in you example ' Rs + j Xs)' I was referring to Rs, which I though
was the antenna resistance, and jXs the capacitive or Inductive reactance,
of which does not
consume any power, but effects the power factor (phase shift) acting on the
real antenna resistance. Which part did I misquote or misunderstand Jim, or
is Rs not the antenna resistance
under the conditions of measurement. ?
Adrian ... vk4tux
-----Original Message-----
From: [email protected]
[mailto:[email protected]] On Behalf Of Jim Brown
Sent: Thursday, 5 March 2020 2:32 PM
To: [email protected]
Subject: Re: [Elecraft] High Current only on 20 Meters
On 3/4/2020 8:15 PM, Adrian wrote:
When I say radiation resistance I include the small copper resistance
also, which is negligible on this heavy copper wire delta loop.
An important part of my post was about using the right words to describe
physical reality. Radiation resistance is a characteristic of an antenna,
and can be used to compute antenna efficiency. That's NOT what you're
measuring. You are measuring feedpoint impedance (assuming you can connect
at the feedpoint AND that your measurement setup doesn't change the
impedance).
So please call it what it is -- the feedpoint impedance, which your analzyer
probably reports as Rs + j Xs). :)
73, Jim K9YC
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