[TenTec] It's getting cold. Perfect antenna weather for a OCF dipole

Rick - DJ0IP / NJ0IP Rick at DJ0IP.de
Sat Sep 19 17:51:50 EDT 2015


Probably nobody on the planet has built and tested more different versions
of the OCFD (Windom) than I have.  I can give you a few pointers here that
you don't read on the W8JI Windom page.  
I got the pointers from W8JI, but not on his windom page.  On another page
his web site.
I used that information to develop several different versions of the Windom.
In the meantime I have made over 1200 measurements of common mode current
and swr on various windom models and have it all available for anyone to

Two key points: 
1.  The Balun is far more important than one might imagine.  99% of ALL
(ALL) baluns used in Windoms are WRONG.  

2. There is no one best feedpoint; it depends on what bands you want your
antenna to cover.

I have so far come up with two versions of multi band 80m windoms which work
superb, but only one works well on 30m, the one W8JI describes.  Mine is
slightly off from his but this small difference may very well be a
difference in wire type and ground condx.  

Here are links to my two antennas:
1.  http://www.dj0ip.de/off-center-fed-dipole/80m-ocf/ 
2.  http://www.aerial-51.com/model-807-ul/ 

NOTE:  Nr. 1 works on 30m but not on 17m;  Nr. 2 works on 17m, but not on
30m.  Both work all other hf bands except 160m.

THE BALUN:  YOU MUST BUILD YOUR OWN.  I know of no commercial balun
manufacturer that builds the right balun for the task if 80m is to be
included.  NONE!  They don't understand the antenna, nor its common mode
current characteristics.  I do.  It took hundreds of hours of research and
field work to sort this out.

Balun manufacturers make false assumptions about the characteristics of
these antennas.  From what they are producing, it is obvious they have never
themselves run extensive field tests on the antennas.  I have.

Most make two mistakes, a couple make only one.  ALL are wrong.

You should use a 4:1 dual core Guanella balun and it MUST have two toroids
and each of the two transmission lines must have its own dedicated toroid.
This will suffice for a 40m OCFD but if it is to cover 80m as well, it won't
have enough CMI.  You will need an additional Maxwell choke directly
attached to the balun.

Because of the enormous common mode current (CMC) in OCFD antennas, you need
a balun with a lot of common mode impedance (CMI) on the lower frequencies.
The higher bands are not affected as much by CMC as the lower bands.

This dictates using #43 cores.  Almost all balun manufacturers are using #61
cores which don't have enough CMI on the lower frequencies.  Do not use #31.
Although it eliminates the need for the extra Maxwell choke on the low
bands, it does not provide sufficient CMI on the high bands.   Build it as I

The down side of using #43 is, its Curie point is considerably lower than
that of #61, so if you want to run very high power, you will have to double
the cores (total 4).  For each half, glue two FT-240-43 cores together.  If
you want to run legal power RTTY, you will need 6 cores; 3 in each stack.

Use only Teflon insulated wire.  Should be a no-brainer but some big name
companies fail to do this.

If you do your homework, plan your antenna and execute as I have described,
you will be rewarded with a 7 band antenna which does not even need an
antenna tuner on most bands.  It does of course on 80m if you want to cover
the whole band.

Another important point.  Regardless of where you like to work on 80m, the
antenna must be built to resonate at the bottom of the band, around 3.5 MHz.
Otherwise it will be resonate above the bands on the higher bands.  After
you get the antenna built, tested and working, I can show you a trick to
move JUST THE 80M resonance to where you want it, without affecting the
other bands much.

BEWARE OF THE WALTER MITTY's out there, who think they know better because
they read it somewhere.
My recommendations are based on my more than 1000 hours of work on this type
of antenna over the past 4 years - not something I read somewhere.

73 - Rick, DJ0IP
(Nr. Frankfurt am Main)

-----Original Message-----
From: TenTec [mailto:tentec-bounces at contesting.com] On Behalf Of Mike Bryce
Sent: Saturday, September 19, 2015 9:47 PM
To: tentec at contesting.com
Subject: [TenTec] It's getting cold. Perfect antenna weather for a OCF


It's been way to quiet here. 

With fall only a week away and winter not too far behind, it's a great time
for antenna work. 

I'am going to out up a off center fed dipole. 

After reading pages after pages of information about this antenna it seems
to work differently depending to quite a few factors. 

Such as how high up, gauge of wire, insulated or not and of course the feed

>From what I've read, 137' wire. Short end about 42' 

(All lengths are for example only!)

Now according to W8JI, he suggest the short end should be 24' 

Has anyone built a OCF dipole to W8JI dimensions? 

According to his web page, the above feed point will get me 30 meters. I'd
love to put my Argonaut VI on 30 meters this fall. 

I've got the wire a good 4:1 current balun and a rainy Sunday. 


from my iPhone
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