[Elecraft] KX3 & Chasing local HF noise sources

[Vic Rosenthal K2VCO]

It appears to me that "no-radial" verticals are also OCF dipoles, 
vertically oriented. In my new QTH I will be limited to a vertical, and 
I chose a Cushcraft (well, MFJ now) R8. It has a built-in 'balun' -- 
that is, a choke -- but I am taking no chances and have prepared another 
choke that I will mount immediately under the antenna to ensure that it 
will be decoupled from the feedline.

In addition, I am going to put yet another choke in the line where it 
enters the shack. I made these according to GM3SEK's designs 
<http://www.ifwtech.co.uk/g3sek/in-prac/>, so they won't cost a king's 
ransom.

I hate noise!

On 5/1/2014 11:14 PM, K8JHR wrote:
> K9YC raises an important issue.  I love my OCF dipole, but only because
> I was very careful in how it went up.
>
> My friend in Germany is making a serious study of common mode noise on
> OCF dipoles, and from his work I know you must bring the transmission
> line away at a 90 degree angle, and use a good 4:1 balun with common
> mode choke, or the OFC Dipole can be an inherently noisy thing - in
> fact, causing its own noise!
>
> I have a very quiet OCF dipole, but I was extremely particular in how I
> assembled and hung it, with a good balun-common mode choke, and making
> sure I did not have have a problematic length of transmission line, etc.
>     Great antenna, I use it as net control of a nationwide net, but you
> must be careful in how you build it.  If the coax comes near the
> elements, even just a little, it can become problematic - affecting SWR
> if not causing audible RFI.
>
> Even if you put up resonant half wave dipoles, follow Jim's advice and
> use a common mode choke.  Some guys put chokes at both ends of the
> transmission line - at feed point and near the shack - and I know of no
> negative or down side from doing that.
>
> In addition to what Jim refers you to, in general, see:
>
> www.dj0ip.de
>
> and in particular see:
>
> http://www.dj0ip.de/off-center-fed-dipole/what-s-wrong-ocfd/
>
> which is all in English, and the author makes the case that many times
> the 4:1 balun is poorly constructed or improperly wound to minimize
> noise and effectuate the proper transformation.   And he uses 2 OCF
> dipoles, himself, so it can be done with good results.   It seems that
> some things called a "balun" are transformers and other things called a
> "balun" are common mode chokes, and sometimes you need both functions,
> and how yours is made matters.  So, read Jim's article, and the other
> references herein, and maybe check out  W8JI's personal web site, for
> good information on this.
>
> Just MY take.
>
>
> ===============  K8JHR  ================================

-- 
73,
Vic, K2VCO
Fresno CA
http://www.qsl.net/k2vco/