James,
There is no need to separate the two toroids more than they are separated
inside that balun.
That is the one nice part about using toroids.
Separation need only be about 2x or 3x the diameter of the wire, and you
already have the insulation between them, so you only need a couple mm more
separation.
One of the Balun Designs baluns does the same thing (don't recall the model
number).
I also did the same thing on Ver.-3.1 of my 40m Ultra light OCFD.
In Ver.-3.2 I moved the 1:1 current choke to about 2" below the 4:1, but it
made no difference.
Pictures here: http://www.dj0ip.de/off-center-fed-dipole/40m-ocf/version-3/
BTW, the problem I speak of in the conclusion on Ver. 3 was fixed when I
built Ver. 4.
What did I do? I changed from using a single toroid in the 4:1 balun to
using two toroids in it. The 1:1 is shown there hanging below. This
particular antenna has an awful lot more common mode current than a dipole,
due to its lopsided split. It's cases like this where you see the
difference between using the correct balun design, and taking a shortcut.
On the other hand, Ver. 2 of that antenna used a single toroid 4:1 balun
(the shortcut) and had no CMC problems. But it had a much more gentle
feedpoint split and far less CMC to start with. Ver.-2 is pictured here:
http://www.dj0ip.de/off-center-fed-dipole/40m-ocf/version-2/
As I said, define the antenna first, THEN you can say which balun technology
is necessary.
73
Rick, DJ0IP
-----Original Message-----
From: TenTec [mailto:tentec-bounces@contesting.com] On Behalf Of Richards
Sent: Sunday, July 28, 2013 9:10 PM
To: Discussion of Ten-Tec Equipment
Subject: Re: [TenTec] which balun?
On 7/28/2013 5:46 AM, Rick - DJ0IP / NJ0IP wrote:
> James,
>
> Good news, bad news on your suggestion to use two separate baluns for
> the job.
>
> The good news is, your suggestion to use two baluns is a great idea.
> The bad news is, even though you probably concluded this on your own,
> it is not a new concept.
Of course it is not a new idea... I am not
that schamart ! ;-)
> In fact it was described at great lengths in the Sep/Oct 2005 issue of
> QEX magazine.
Shoot... that would pretty much squelch
my patent application... ;-)
> In this article, Andrew introduces the idea of a Hybrid Balun.
> However, in reading his conclusion, he says it maintains a good
> balance and good rejection of common mode current across a wide range of
high impedance.
Interesting article, except for all the math...
Given his results, I still wonder whether
it would be even better if the two were
separated by some grater distance, and housed
in separate containers. Putting all one's
eggs in just one basket, I wonder where there
is some deleterious interaction between the
two.
----------------------- K8JHR -------------------
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