Hi Joe,
I understand about the line loss, and what it does, but aren't you still
finding the "resonant" freq. of the antenna by finding where the VSWR dips?
Assuming you didn't screw up in constructing the antenna, and that you are
measuring with whatever feed line you plan to use, isn't it the SWR at the
transmitter (or the return power) that you are concerned with? If your rig
is happy (you aren't burning up your finals or the power is not folding
back) and you have feed line appropriate for the distance and frequency, and
you didn't screw up building the antenna, then all you want to do is make
the minor adjustments necessary to get that dip at the desired point in the
band.
It's sort of like having an antenna tuner (coupler, or whatever you want to
call it). You aren't really tuning the antenna; you are just making the rig
happy. Ideally the tuner would be at the antenna to reduce feed line loss,
or better yet, you actually COULD tune the antenna, like a StepIR or a
Screwdriver, but assuming those aren't options available to you then
whatever makes the rig happy should be fine, right? Obviously, a dummy load
will make the rig happy, but I mean assuming you have a decent antenna and
appropriate feed line.
What am I missing?
73 - JC, K0HPS
-----Original Message-----
From: Joe Subich, W4TV [mailto:w4tv@subich.com]
Sent: Sunday, September 03, 2006 1:01 PM
To: 'JC Smith'; towertalk@contesting.com
Subject: RE: [TowerTalk] C31 - 1 feed line or 3
JC,
The issue with "at the feedpoint" vs. Force 12's specifications
which call for 100' of coax is LOSS. Loss in the coax, even 1 dB
in 100' for RG-213 at 28 MHz, causes the apparent SWR and SWR
bandwidth to be significantly better than it really is.
An antenna system with feedline loss of 3 dB (100' of RG-58 on
10 meters) will never show a SWR worse than 3:1 - no matter how
bad the antenna really is.
73,
... Joe, W4TV
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com] On Behalf Of JC Smith
> Sent: Sunday, September 03, 2006 2:36 PM
> To: n8de@thepoint.net; 'N2TK, Tony'
> Cc: 'Ron Feutz'; towertalk@contesting.com
> Subject: Re: [TowerTalk] C31 - 1 feed line or 3
>
>
> Just out of curiosity, how do you make those measurements at
> the antenna
> without your body affecting the results? On many antennas it
> is almost
> impossible to position yourself at the feed point anyway, and
> in any case,
> isn't it the whole system (antenna, support, feed line, etc.)
> we are really
> concerned with? Who cares where an antenna with no feed line
> resonates
> (other than the theoreticians). Not a criticism of your
> comment, Don, I
> believe you are correct in what you say, but what does it really mean?
>
> 73 - JC, K0HPS
>
>
>
> -----Original Message-----
> From: towertalk-bounces@contesting.com
> [mailto:towertalk-bounces@contesting.com]On Behalf Of Don Havlicek
> Sent: Thursday, August 31, 2006 8:24 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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> >
> >
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> >
>
>
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