[TowerTalk] homebrew 1:1 current balun

[Roger (K8RI) on TT]

I have 6 turns of LMR-400 through a stack of 5 2.4" cores.  I'm pretty 
sure I could get another turn using a bit of wire pulling soap / lube.  
Using RG-400 Teflon dielectric and silver plated braid should easily 
double the number of turns.
http://www.rogerhalstead.com/ham_files/AntennaFeed1.htm  The 
perspective  from the photo doesn't show how the coax loops up and then 
down to the insulator.  The braid and center conductor are thoroughly 
waterproofed to prevent the wicking of moisture, plus any that got in 
would need to go up hill for several inches.

I prefer to just make the choke part of the feed line.  You do need to 
figure the length of coax per turn, but by threading the coax through 
the cores you have less worry about the choke supporting the feed line.  
Using RG-400, requires that the feed line be supported, complicating the 
construction a bit.  Using the DX Engineering photo of the interior of 
their choke gives some good pointers on strong construction.

Wait a minute!
When looking at the photo, I realized I have 7 turns, not 6. There are 6 
loops visible + 1 for the pass through to the antenna. According to 
pages 39 and 40 of the tutorial, I should have about 7,500 ohms 
isolation although Jim came up with a different number.  That antenna 
can be easily raised and lowered so I'm thinking of two approaches.  A 
binocular approach with 8 cores (2 sets of 4 cores) and 7 turns.  That 
arrangement makes it much easier to get 7 passes through the cores and 
very close spacing on the turns.

I also have a stack of 7 cores with 1/8th in spacing, using Lexan 
spacers that can be put into a box like the DX engineering assembly.

Will I get it done?  Only time will tell.

73

Roger  (K8RI)

On 11/30/2015 6:11 PM, Jim Lux wrote:
> On 11/30/15 9:17 AM, Jamie Tolbert wrote:
>> What tpe beads do I need, 43 or 73? length? 4 ft, 100 beads seems 
>> awfully long.....
>>
>> ____________
> I use 31 mix for this kind of choke application.
>
> what is your operating frequency?
>
> http://audiosystemsgroup.com/NCDXACoaxChokesPPT.pdf
> see pages 22-25
> 73 is better in general, 43 is ok for low frequencies
> 31 isn't great for bead baluns..
>
>
> Have you considered using a 2.4" toroid core(s) and running multiple 
> turns of the coax through it.  I can get about 10-12 turns of 1/4" 
> diameter coax (RG58 type) through those cores. I think you can get 3-5 
> turns of 0.405" coax (RG213 type) through it.
>
> There's a fairly decent cookbook for this kind of thing, with all the 
> measurements on actual chokes, etc. in Chapter 7 of 
> http://www.audiosystemsgroup.com/RFI-Ham.pdf
>
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>
>
>
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-- 

73

Roger (K8RI)


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