[TowerTalk] TH7DX Balun Was W1JR, Now BN-86

[Gary Schafer]

I don't know about that one but I can tell you my experience with a 
mosley TA33. They have a balanced feed. However they recommend grounding 
one half with a small strap to the boom. That makes it unbalanced. I 
tried it with their recommended coax coil balun. Very flat and broad 
band but it had two resonant points! one was in each ham band and a 
second well below the band. I can't help but think that the pattern 
would be distorted like that.
I called the factory about it and they pled ignorance.
I removed the shorting strap so the feed was balanced and the bandwidth 
went down and the second resonance went away. The antenna had sharper 
swr curves this way as one would expect.

Moral of the story: tune a little farther and see if this kind of thing 
is going on.

73
Gary  K4FMX

Jim W7RY wrote:
> Well team....
> 
> 
> I know we tossed this one to death many times before... But here is what I 
> just found on my TH7.
> 
> I installed a home brew W1JR type balun on my TH7 when I put the antenna up 
> last year. I was not happy with the SWR curves when I tested the antenna 
> after installation. I finally decided to do something about it.
> 
> I just removed the W1JR type balun and installed a Hy-Gain BN-86.
> 
> The SWR curves now measure about the same as what is spelled out in the 
> manual. Before, the SWR on 20 meters was never below 2:1. And on 15, it was 
> never lower than 2.5:1 anywhere in the band.
> 
> 
> When I was testing the W1JR type with  my MFJ 259 on top of the tower, I 
> noticed that the impedance would never drop below 40 Ohms. With the BN-86, 
> now it will.
> 
> The W1JR balun is home brew. 7 turns of RG-142 on a FT-240-61 core wound 
> all on the same side of the core. Not a cross over type winding.
> 
> The balun was installed into an outdoor plastic electrical box with brass 
> studs through the sides for hooking to the matching section of the TH7. I 
> used the same RG-213 coax jumper from the end of my 1/2" Heliax to the 
> balun. No other changes... Just replaced the balun.
> 
> I know that Steve, K7LXC, mentioned in the tri-bander report that they had 
> some difficulty with the balun selection on the TH7.
> 
> 
> Hmmmmmm....
> 
> 73
> Jim W7RY
> 
> 
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