At 11:33 AM 9/1/2006, Don Havlicek wrote:
>When measuring the 'resonance' of an antenna at the shack, you are NOT
>measuring the antenna's resonance .. you are measuring the resonance of
>the antenna and feedline.
>Remember .. the feedline SHOULD have NO effect, but it will, unless it
>is an exact 1/2-wavelength multiple at the particular frequency at which
>you are making measurements.
Depends if you're measuring dips in SWR or actual resonance (i.e. no
reactive component in impedance).
If you're measuring the SWR (not the R+jX) at the shack end, the
transmission line just moves the apparent R+jX around a circle of constant
SWR (ignoring TL losses). That is, the TL doesn't change the SWR, so a dip
at a given frequency is still a dip. (assuming the TL's not radiating)
If you're measuring the reactive part of the impedance, then, yes, the TL
makes a huge difference.
>Don
>N8DE
>
>Keith Dutson wrote:
> > What changes the resonance at the shack?
> >
> > 73, Keith NM5G
> >
> > -----Original Message-----
> > From: towertalk-bounces@contesting.com
> > [mailto:towertalk-bounces@contesting.com] On Behalf Of Don Havlicek
> > Sent: Thursday, August 31, 2006 10:24 PM
> > To: N2TK, Tony
> > Cc: 'Ron Feutz'; towertalk@contesting.com
> > Subject: Re: [TowerTalk] C31 - 1 feed line or 3
> >
> > Where did you make those measurements?
> >
> > If at the shack end of the coax, they are quite meaningless as to antenna
> > resonance.
> >
> > The only way to get the correct measurements is AT THE ANTENNA.
> >
> > Sorry, but too many guys/gals put their SWR meters at the shack end of the
> > coax and try to determine what the ANTENNA looks like from there.
> >
> > It just doesn't work that way.
> >
> > Don
> > N8DE
> >
> > N2TK, Tony wrote:
> >
> >>Ron,
> >>Mine resonates at
> >>
> >>28.64 - 1.1:1
> >>21.22 - 1.25:1
> >>14.1 - 1.2:1
> >>
> >>Single feed.
> >>
> >>N2TK, Tony
> >>
> >>
> >>-----Original Message-----
> >>From: towertalk-bounces@contesting.com
> >>[mailto:towertalk-bounces@contesting.com]On Behalf Of Ron Feutz
> >>Sent: Friday, September 01, 2006 10:02 AM
> >>To: towertalk@contesting.com
> >>Subject: [TowerTalk] C31 - 1 feed line or 3
> >>
> >>TT'ers,
> >>
> >>I just ordered an F12 C31XR. I have been told by experienced users
> >>that the beam can be a pain to tune properly on 15 (high swr).
> >>
> >>I ordered the beam with single feed. Since then I have heard that the
> >>problem is less severe with the 3 feedline model.
> >>
> >>All inputs from experienced users will be welcomed.
> >>
> >>Thanks and 73,
> >>
> >>Ron KK9K
> >>
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> >
> >
> >
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