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.
73's and Aloha,
> Sounds like you are having fun. I am in the process of putting up a C4E. I
> also snapped one of the Aluma-Weld wire. It seems pretty easy to do.
> Luckily, I did not need a new one. Still had enough length to make it
> What distance did you end up with from the spreader bar to the tuning bars?
> Did it match at all with what is in the assembly manual?
> I have initially placed the tuning bars about 17" from the spreader bar. My
> lowest SWR is about 1.6 at 6.9 MHz with the C4E hanging on a tilted over
> tower. The 40m element is only about 6 feet off the ground. I know that the
> SWR will change when I get the antenna up in the air, but do you have any
> idea how much the center frequency will change?
> TNX in advance de KJ7GU,
> John in Arizona.
> ----- Original Message -----
> From: Stuart Browne <firstname.lastname@example.org>
> To: towertalk <email@example.com>
> Sent: Sunday, November 21, 1999 11:21 PM
> Subject: [TowerTalk] F12 C4XL Assembly and Tuning Love Story
> > I just completed constructing a F12 C4XL.
> > The antenna went together really well. The instructions were pretty
> > straight forward. Riveting the elements was fun and not hard to do. The
> > elements were all well marked, pre-drilled for the rivets and telescoped
> > for easy to assemble.
> > I assembled all of the elements and the boom in my driveway and then
> > carried everything up to my roof. The roof is only slightly sloped so
> > its perfect for assembling beams. I used three plastic/foldedable saw
> > horses which I layed out and assembled the boom on. Then I added the C3
> > and C4 elements, the C4 40 meter "spreaders", and after a little head
> > scratching (the photos in the assembly manual were hard to read) the
> > Aluma-weld wire and the linear loading elements for the 40 m elements.
> > On the 40 m reflector I snapped two of the Aluma-Weld 40 m elements
> > connecting them to the spreader. I called F12, and they sent me a free
> > set of replacements via 2nd day air so I had a few extra days of
> > anticipation.
> > Using the MFJ analyzer I checked the VSWR on the C3 portion of the beam
> > and all of the VSWR was 1:1 or 1:2...right on the frequencies where I
> > want to operate. The C4 portion of the beam took a little time to "tune
> > and prune" . Tuning which consists of setting the linear loading
> > elements per the manual and the adjusting them for the frequency you
> > want. The frequency as per the book setting where I found unity was 6.3
> > mHz., a little out of band even for KH6 ! It took less than an hour to
> > adjust the linear loading elements and the hair pin matching coil until
> > I found a 1:1 reading at 7.1 mHz. I painted the boom with a very light
> > blue paint and then with spray cans of green, grey and sand, camoflaged
> > it to look like my Hawaiian hillside of Hale Koa scrub.
> > The beam goes up next week on the 50' pirod tower (two -20' sections and
> > a 10 foot mast) and will be turned by a Hygain HDR-300, a bit over kill,
> > but I live on a steeply sloping hillside on the "Windward" side on the
> > island of Oahu and this is hurricane country. Serious on-air testing
> > and comparison to my super quite trap dipole and ancient TA-33 jr.
> > next weekend. This has been a fun project!
> > 73's and Aloha,
> > Stu
> > WH6H
> > --
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