My guess is the velocity constant(Vo) for the replacement (RG-8) was not the
same as the Vo of the coax replaced (RG-58), if this is indeed the fact,
then the physical length of the RG-8 would not be equal to the physical
length of the RG-58 for the "same electrical length".
It would appear that you need to adjust the length of the RG-8 so that it is
electrically equal to the replaced RG-58. This is assuming that there is no
problem with the new connectors.
I hope this may lead to a solution to your problem and you will be back on
12 meters shortly.
73,
Jim WD4AIR
>From: Alan Bryant <wd0evx@moonworks.com>
>To: tentec@contesting.com
>Subject: [TenTec] Antenna Matching Weirdness
To: <tentec@contesting.com>
>Date: Wed, 18 Oct 2000 18:17:10 -0600
>
>
>I realize that by posting this, I'm probably going to look like an idiot,
>but I'm sincere in wanting to know what's going on with something.
>Hopefully someone smarter than I am can provide an intelligent answer. So,
>from the "there are no dumb questions" department...
>
>I use a multiband MFJ vertical for an antenna (it's all I have space and
>neighbor tolerance for), and a small antenna tuner with it to broaden its
>bandwidth. The antenna is designed for 40m through 10m, plus 6m and 2m,
>EXCLUDING the WARC bands.
>
>When I initially set-up my station, the only short coax patch cables I had
>with PL-259s on them were made of RG-58 coax, but since it was only a
>couple of 2' cables, I used them anyway. All seemed to work well enough,
>and the tuner also allowed me to match with low SWR on the WARC bands in
>addition to the others. While I know the antenna is far less than optimal
>on the WARC bands, I've managed to work some DX with this set-up on 12m
>with relative ease.
>
>I recently made new patch cables using RG-8 foam core coax, cut to the
>exact lengths I needed. Not surprisingly, the configuration of the three
>tuner knobs was now different to achieve low SWR. But suddenly, I can no
>longer successfully match on 12m at all. The lowest SWR I can get there is
>about 3:1, when I could get it clear down to 1:1 before.
>
>Understanding that trying to use this antenna on the WARC bands is probably
>dumb to start with, I'm still left wondering why I could match it
>successfully with crappy, inappropriate coax (RG-58), and now I can't when
>using quality coax connections of the proper type (RG-8).
>
>Any thoughts on this are welcome (except those, perhaps, telling me I
>shouldn't expect it to work to begin with).
>
>Thanks.
>
>
>
>---
>Alan Bryant, WDØEVX
>Denver, Colorado
>http://www.moonworks.com/wd0evx
>
>
>--
>FAQ on WWW: http://www.contesting.com/FAQ/tentec
>Submissions: tentec@contesting.com
>Administrative requests: tentec-REQUEST@contesting.com
>Problems: owner-tentec@contesting.com
>
_________________________________________________________________________
Get Your Private, Free E-mail from MSN Hotmail at http://www.hotmail.com.
Share information about yourself, create your own public profile at
http://profiles.msn.com.
--
FAQ on WWW: http://www.contesting.com/FAQ/tentec
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
|