[TowerTalk] Force EF-140S

[Mark Beckwith]

> Toying with the idea of converting a linear loaded
> EF-140S, which is part of my C3E, to a stand-alone
> inductance loaded dipole.  Has anyone tried this
> with any success?


I have done that with Hygain and KLM shorty-forty elements, both.  (I.e. if 
I'd have had Force-12 elements lying around I would have used them)  I 
removed the factory linear loading, then handmade small loading coils that 
mounted on the elements out where they have the insulators that were at the 
end of the linear loading.  (This may not be what you had in mind, though, 
because) I also added about 12' of tubing at the center of each element 
half, so the elements are more like 85% full sized - which also makes the 
loading coils smaller and less of the overall electrical length of the 
antenna (all to the good).

http://www.n5ot.com/n5ot/EU40.JPG
http://www.n5ot.com/n5ot/JA40.JPG
http://www.n5ot.com/n5ot/Extreme Danger.jpg

The loading coils are RG58 wound over PVC - I think it's about 1.5" ID PVC 
(schedule 40), and the ones on the directors are maybe 6-7 turns and the 
ones on the reflectors are maybe 20-30 turns.  The physical lengths of all 
the elements in a given beam are the same - the resonant frequency of the 
elements is set by the number of turns.  I built a set of coils with an 
adjustable tap, and then put an element up and found the dip, brought it 
down and adjusted the tap, then repeated the process until I know how many 
turns = what frequency.  Then I just built fixed coils, built the antennas, 
put them up and didn't look back.

I knew what frequency to set the elements to by designing a computer 
optimized yagi, then worked the design backwards to learn the resonant 
frequency of each element.

In the photos you can see the little bumps where the home-made loading coils 
are located.  Some people have stated that what I did should not have worked 
but I think they're engineers.  Something about Q and blah-blah-blah all 
that and I think they used the words "impedance" and "efficiency" or 
whatever, but I'm happy with the way these antennas have played.  They 
definitely make a lot of QSOs and bust a lot of pile-ups.  People tell me my 
signal is loud I don't run excessive power.

This would be pretty simple to do with one element, and I don't think 
getting a match when you had the element resonating on the frequency you 
liked would not be hard, even if the element were shorter and the coil 
longer.  Personally, after getting the frequency set, I would just use a 
tuner and get on the air.  Life is short - get on the radio.

Mark, N5OT


----- Original Message ----- 
From: "jsloss" <k7mks at comcast.net>
To: <towertalk at contesting.com>
Sent: Wednesday, November 14, 2007 11:50 PM
Subject: [TowerTalk] Force EF-140S


>
> Joe k7mks