Using a single feed, my C-31XR resonated (measured in the shack, where my
transmitter is) well below 21.0 MHz (209??). N6BT suggested cutting an
inch, I think he said, off the end of each side of the 15M driven element.
At the time, I did the math and came to the conclusion that I needed to take
off more length to get the resonant frequency high enough in the band.
I loosened the boom guy and rotated the room 90 degrees so the elements were
almost vertical. I carried a cordless drill up the tower to the first
element tip and drilled out the rivet holding the last/smallest tube and
removed it. I then did the same for the other side of the element. I
didn't change the lengths of any parasitic elements.
I no longer have the antenna and can't find my measurements, but my
recollection is that it covered from the bottom end of 15M through most, if
not all, of the phone band.
Again, if I am remembering correctly, the 15M driven element has no direct,
electrical connection to the coax, but is capacitively coupled to the 20M
driven element using a single feedline. The 10M driven element is connected
to the 20M DE with two, parallel wires that I tried to stretch taut to keep
parallel. If I were to put up another C-31XR, I'd probably use three feed
lines to a remote switch. It would be interesting to try a remote switch
that can be configured to either float or ground the unused ports to see if
any difference.
Jim N7US
-----------------------------------------------------------------
N2TK:
Ron,
Mine resonates at
28.64 - 1.1:1
21.22 - 1.25:1
14.1 - 1.2:1
Single feed.
N2TK, Tony
-----------------------------------------------------------------------
KK9K:
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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