[TowerTalk] RE : Understanding Antenna Impedance Measurements
on4kj at skynet.be
Tue Nov 15 19:22:38 EST 2005
So I guess :
" If one doesn't get through the trash with 100W it wont be much better
with 200W ".
But there are all kind of HAM........ Nowadays even more then thirty or
forty years ago.
Seen from the technical point of vieuw, I love these kind of threat,
because the approach of a problem comes very often from an other
direction and helps a lot for a better understanding. ( Even at my age
I still look out for these messages.
De : towertalk-bounces at contesting.com
[mailto:towertalk-bounces at contesting.com] De la part de Tod
Envoyé : mardi 15 novembre 2005 22:56
À : 'Tower Talk List'
Objet : Re: [TowerTalk] Understanding Antenna Impedance Measurements
In the end it is transferring power to the antenna that counts. Unless
the VSWR is awfully high and/or the line length is very long I think it
is quite stuffiest to put a tuning network at the station so the
transmitter is happy and then start sending. You most likely ( and the
folks you contact) will never know that your antenna is neither resonant
nor matched at the frequency you are operating -- and you signal will
not be noticeably impaired either.
> -----Original Message-----
> From: towertalk-bounces at contesting.com
> [mailto:towertalk-bounces at contesting.com] On Behalf Of Jim Brown
> Sent: Tuesday, November 15, 2005 3:50 PM
> To: Tower Talk List
> Subject: Re: [TowerTalk] Understanding Antenna Impedance Measurements
> On Tue, 15 Nov 2005 15:38:28 -0700, Tod wrote:
> >Those values look like they are within about 2% of expected
> values for
> >the R and within 20% or so on the X. Is the analyzer accuracy any
> >better than that if there is NO coax between the load and
> the analyzer?
> What Jim Lux has shown by cranking the numbers is that when
> the VSWR is small, the effect of the transmission line is
> small. That would be true whether the line was a half wave or
> not. But when it's a half wave length, it has almost the
> effect of moving the analyzer to the antenna terminals AT
> THAT FREQUENCY.
> I say "almost" because the loss in the line will reduce the
> VSWR slightly (but VERY little on topband).
> Tom can tell you a lot more about analyzer errors. But
> consider this -- it isn't really possible to stick the
> analyzer at the antenna and read it without a very tall
> ladder, and your presence next to the analyzer will detune it
> a bit. There's also the interaction of the antenna with the
> coax. Other errors
> -- the analyzer has some finite input R and C. For small
> VSWR, neither mean much, especially at 2 MHz, but they sure
> do at higher frequencies and high VSWR. As I recall, W4EF
> said that the AEA CIA-HF has input Z on the order of 10-12K
> in parallel with 12 pF. That's an older box, and the new one
> may or may not be better.
> Jim K9YC
> See: http://www.mscomputer.com for "Self Supporting Towers",
> "Wireless Weather Stations", and lot's more. Call Toll Free,
> 1-800-333-9041 with any questions and ask for Sherman, W2FLA.
> TowerTalk mailing list
> TowerTalk at contesting.com
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any questions and ask for Sherman, W2FLA.
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