[TowerTalk] TowerTalk] F12 EF-240/230

[K7LXC@aol.com]

In a message dated 10/21/2005 8:33:06 PM Pacific Daylight Time, 
towertalk-request at contesting.com writes:

>   I have assembled a Force 12 EF-240/230 (2 element 30 & 40 Mtr on a common
boom) and have suspended it up 25 feet on a rope between two trees.  I am
unable to get the antenna resonant at a frequency that is in either band.
Email to F12 three days ago was not answered.

>  The best tuning is about 1.25 @ 6.7-6.8 Mhz and quite narrow.  On 30 it is
1.5 @ 9.8 Mhz.  I do not seem to get the resonant frequency above those
listed.  I have tried moving the linier jumpers so they are quite a ways off
what the manual quotes but it does not seem to make much difference.  I am
using a MFJ259B on about 35 feet of coax.

    The F12 linear loaded antennas are not easily tuned and the dimensions 
they provide are just a STARTING point for the jumpers. They aren't like most 
other antennas where the dimensions are really meaningful.

    You have to tune each element individually. The driven element is obvious 
and then take the shorting piece of wire off of the reflector and tune it 
like a dipole. The resonant frequency of the non-driven elements are in the 
manuals so you just just tune them for those freqs - typically 2-3% longer than the 
DE. Don't forget to put the wire jumper back on. 

    If the DE and REF are tuned closely in frequency, you'll have good swr 
but very narrow bandwidth. 

Cheers & GL,
Steve    K7LXC
TOWER TECH