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Re: [TowerTalk] Balun Recommendation

Subject: Re: [TowerTalk] Balun Recommendation
From: Jim Brown <>
Date: Mon, 16 Apr 2012 13:10:10 -0700
List-post: <">>
On 4/16/2012 11:15 AM, Steve Hunt wrote:
> Here's one commercial balun manufacturer that_does_  publish useful
> performance data:

It's good to see that.  One concern and one quibble. First, the quibble 
--  I have a strong preference for data like this to be plotted with a 
log frequency axis.  Second, the concern.  I have a strong mistrust of 
impedance data obtained by reflection-based methods (i.e., S11). I don't 
know the AIM unit well enough to know how this measurement may have been 
taken, but from the work I've done, some form of S21 measurement is 
needed to get good data. I've addressed this in the tutorial.

3-4 years ago, several of us did a "round-robin" measurement of an 
unknown choke (as I recall, 14 turns on a 2.4-in toroid that I suspect 
was #61 or something like it) by a variety of methods. The least 
accurate measurements were done with an AIM unit, and the data were 
WILDLY inaccurate. The best agreement was between my simple 
generator-voltmeter method and by someone using a Q-meter.

I just looked at a photo of the product in question.  Choking impedance 
looks quite good, but I'd be surprised by this data if the core is 
Fair-Rite #31.  Nothing wrong with that if they've got a better 
material.  I AM concerned with a 5kW power rating for a choke with this 
graph of choking Z vs frequency.  While it would probably do fine with 
1.5kW .in a well balanced system, I would expect it to fry pretty 
quickly with much imbalance and the "wrong" length of transmission line. 
It's nothing more complicated that E squared / R, where E is the common 
mode voltage across the choke and R is the parallel equivalent R in the 
equivalent circuit of the choke.  G3TXQ, W8JI, and I have had some 
pretty spirited discussions on this matter, and there's a discussion of 
this both in the RFI tutorial. and the Chokes Power Point.

73, Jim Brown K9YC

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