Topband: Recommendations on high-power 1:1 balun for 1.8MHz that shows high-Z to RF wanted

[Jim Brown]

On 6/8/2011 6:56 AM, Steve Ireland wrote:

> I am the process of replacing the existing 1:1 high-power current balun on
> my 1.8MHz inverted vee dipole and would ideally like the replacement to have
> something approaching 5,000 ohms impedance at 1.8MHz.   As a result I have
> been looking for information about the impedances of some of the more
> popular, reputable baluns on 1.8MHz on the web, but without success.

That's because they aren't very good. :)

> One of the major candidates under consideration is the DX Engineering
> DXE-BAL050-H10-A - if anyone has measured the impedance of this balun at
> 1.8MHz, I'd be delighted to hear of what the results were.

I've measured several of the DXE models.  While they are well built and 
robust with respect to power handling, their choking impedance is far 
less than what you want.

> suggestions/recommendations as to which 1:1 high-power balun to buy or build
> that displays a 5,000 ohm impedance or so on 1.8MHz would also be much
> appreciated.

A 1:1 "current balun" is really a common mode choke. See my Choke 
Cookbook for several chokes you can build at very low cost that will 
meet your specifications, and that will handle legal ham power levels. 
It's part of my RFI tutorial, which also addresses common mode chokes 
based on ferrite cores  http://audiosystemsgroup.com/RFI-Ham.pdf  
There's also a lot of measured data, You will need to find a source for 
the #31 ferrite cores.  Part numbers are listed in Appendix One, and 
Fair-Rite has a listing of their distributors worldwide on their 
website.  There's also a Power Point presentation on my website that 
I've done for several ham clubs and conventions that includes more 
photos and applications ideas.  http://audiosystemsgroup.com/publish.htm

Here in the US, a lot of ham clubs have organized group purchases of the 
#31 cores and clamp-on parts that are suitable for building these chokes 
(and for fixing RFI problems).  When you're ordering 500-1,000 pieces, 
the prices come WAY down, you can buy direct from the distributor, and 
you can order virtually any product in the manufacturer's catalog.  
About five months ago I organized a group purchase for several local ham 
clubs. We bought 1,100 #31 2.4-in o.d. toroids for just under $4 each, 
including the cost of shipping.  Ham vendors typically sell the same 
part for about $15 plus shipping.

73, Jim Brown K9YC