That's a gracious comment, and I genuinely appreciate it - thank you!
But I wouldn't want Dean or anyone else thinking that I was that clever :)
I was never considering differential dissipation in the choke. My point
all along was that common-mode voltage is determined by
differential-mode voltage: double the differential mode voltage in a
system without changing anything else and the common-mode voltage will
double. The differential-mode voltage in its turn is determined by the
differential-mode load impedance, as is the SWR on the feedline. There
are therefore dependencies between the load impedance, the SWR seen on
the feedline, the common-mode voltage, the common-mode current and the
choke dissipation, which is why I baulked at your original statement
that: "SWR has NOTHING to
do with dissipation in a common mode choke". Please note I am _not_
saying that standing waves are the _cause_ of common-mode current - I
made that clear in an early posting!
You and Ian make valid points about the complex inter-relationships
between the various elements of an antenna system, which is why I
eventually quoted the results from an EZNEC model rather than using a
simpler, less complete analysis. If you remember, a relatively small
shift in frequency on an 80m coax-fed dipole altered the feedpoint
impedance sufficiently that the observed SWR changed from 1.4:1 to 3:1
and the choke dissipation increased from 2.2W to 6.4W.
I fully accept that the increased SWR and the increased choke
dissipation were driven by the increased feedpoint impedance, but then
to say that SWR has NOTHING to do with the choke dissipation seems to me
an odd interpretation of the results.
We can debate causality at some length, but folk who simply observe that
on their real-life antennas an increase in SWR is accompanied by
increase in choke dissipation will rightly believe there IS a dependency.
In retrospect, perhaps this long discussion resulted from some ambiguity
in the phrase "has nothing to do with" ?
On 23/04/2012 21:25, Jim Brown wrote:
> Chatting with Dean, N6BV, at Visalia over the weekend, he observed that
> Steve Hunt had been including differential dissipation in his discussion
> of the effect of VSWR on dissipation in a choke. My apologies to Steve
> for missing that, and the above discussion is my response to correct for
> that failure.
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