I had the same problem with my C-31XR that I installed in 1999 or 2000 and
took down and sold when I moved from AZ in 2006. I had to remove the tip
tube to raise the center frequency into the 15M band.
Tom, N6BT, subsequently told me that later production changes to the feed
system solved the problem, and that was before he sold the company, of
course.
Jim
-----Original Message-----
I found that my C31XR was also resonant at 21.0 MHz or so. In the end I
adjusted the length of the driven element -- made it shorter by about the
amount the last tip extended from the DE. It was still a bit low and I will
be adjusting it again in July when I work on the Idaho Antennas. I also
found that I needed to make the inductance at the center of the 15m driven
element almost zero to get close to the proper feed point impedance.
I am guessing that there may be some subtle production changes which
occurred when the new Force12 manufacturing was started up. Eventually the
manufacturing problems, if any, will be resolved I am sure.
Tod, K0TO
> -----Original Message-----
> HI
> I installed the Force12 C31XR at 75 feet tall and I have a
> problem in 15M, it resounds in 20.000Mhz and in 21.000Mhz
> have 2:5; when I take out one jumper that connects the
> 10Mdriver with the 20M it downs the SWR in 21.000Mhz to 1:7
> and levels up the SWR in 20M. I don?t know if those jumpers
> made the driver longer and that?s why resounds in the
> 20.000Mhz. I don?t know what to do because it is by the
> manual. Any help will be well received!
>
> Here is a picture: http://users3.jabry.com/wp3c1/Dsc01979.jpg
>
>
> Alfredo Vélez WP3C/NP4DX
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