[TenTec] Zepp?

[Richards]

On 9/14/2014 11:47 AM, Don Jones wrote:
>
> But I would like to try the OCF method mentioned by Rick DJ0IP.
> Sounds like for a 44 ft OCF antenna the feed point would be 19ft/25ft. 
> Correct?
> Hoping I can get 10M to play better and would like better efficiency 
> as compared to a 34 doublet on 30M.

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I have been tracking and following Rick's development of his OCF dipole 
for a LONG time, and he has tested that puppy sixteen ways to Sunday and 
back, in addition to using it on the air in various contests.  I, too, 
am interested in OCF dipole designs because I wanted to get a 40 m OCF 
dipole to also play on 15 m, which is usually not possible.  I cut mine 
at different non-typical feed point 25% to 75%  and got 15 meters to 
play on a 40 meter OCF Dipole - but at some expense to the 6 meter band, 
which usually would be better  (mine has about 5 : 1 SWR on 6 meters, 
and it would usually be lower, if I did not adjust it to make 15 play 
better at about 3.5 SWR) -  I think Rick and I are both interested in 
the same thing - i.e., to experiment with various feed points and 
determine how many bands one can work on one wire.

Another reason Rick's work is interesting, is because these things are, 
as Jim Brown strongly observes, more subject to problems from Common 
Mode Current  than other designs, which can add unwanted electrical 
noise and it can also adversely affect impedance mismatch,  as Rick as 
demonstrated in in dozens of tests.    The goal is, of course, to get as 
many workable bands,  with the lowest mix of SWR and mismatch, as 
possible.   MY goal was simply to get 15 m to play on a 40 m OCF dipole 
- which it usually does not.  I understand Rick's goal was more 
ambitious, to make the most  of a single wire antenna.

What did I learn from his work, and my own research... ?

1)  they ARE subject to CMC if you are not careful;

2)  not all baluns are created equal,

3)  it is often better to wind the transformer bit separate from the 
choke bit, and both are important in their own right,

4)  OCF Dipoles generally work on all "even" harmonic bands,  but with 
some tweaking of the feed point location, they CAN be made to work on 
both "even" and at least some "odd" harmonic bands,

5)  Whilst they work best on the lower bands - closest to the one for 
which they are cut - you see simpler, fuller lobes on those lower 
bands,  and get more, and less uniform,  lobes, on higher bands, and the 
more the thing exceeds a wavelength of the frequency of interest, the 
more this occurs,

6)  similar differences in take off angle seem to occur as you move to 
higher frequency bands,

7)  hanging your OCF horizontally is better than as an inverted-V as 
this helps avoid or minimize the CMC,m

8)  take your feed line away from the elements in a perpendicular 
direction.  Rick's tests indicate  leaning the feed line toward one side 
or the other  alters the CMC/SWR result with measurable impact,  and

9)  the length and type of transmission line may have a substantial 
impact.  You can see this if you play with the ARRL TLW (Transmission 
Line for Windows) program to analyze the impact of different lengths of 
transmission line.  Rick can tell you a LOT more about this than I, but 
as he mentioned, above, a quarter wave length may have a substantially 
different result compared to a half wave length, and various points in 
between.

A web site is dedicated to OCF dipoles, and there is data on many other 
feed point splits - which is where I got the idea to move mine.  He has 
a chart of data on several different OCF feed point splits, which is 
very instructive.

  See here:

http://hamwaves.com/cl-ocfd/en/index.html

I seem to recall W8JI has a nice piece on splitting one 80/20%.

Just MY take...
---------------------------  K8JHR -----------------------------