At 06:55 PM 11/23/1999 -1000, Stuart Browne wrote:
>
> John,
>
>My 40 meter linear loading "jumper" is spaced about 24" on one side and
about
>18" on the other and it appears resonant at 7.1 mhz with a 1:1 at a height of
>20' above ground. The feedback from several C4 owners to my post is that they
>all have their jumpers set at a different spacing. No one seems to have used
>the book setting and found a match at the right frequency. When the beam
goes up
>on the tower the center frequency usually changes by about 15 khz but that
>varies by tower height and ground conditions.
One of the issues may be that there have been some significant variations
in the shape of the rigid jumpers. I had a C-4 which I made into an
EF-240S by adding a second element and boom, and the second element's
jumper was a couple of inches shorter and markedly less "humped" than the
first. I believe that the only way to really be sure of tuning one of
these critters properly is to resonate both the driven element and
reflector at their respective target frequencies, while in place on the tower.
73, Pete N4ZR
Sometimes a tower is just a tower
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