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Re: [TowerTalk] Balun Recommendation

Subject: Re: [TowerTalk] Balun Recommendation
From: Steve Hunt <>
Date: Mon, 16 Apr 2012 22:27:05 +0100
List-post: <">>

On 16/04/2012 21:10, Jim Brown wrote:
> 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.

I see reasonable agreement between measurements I make on my AIM and the 
results I get using a signal generator/scope method, provided the AIM is 
calibrated accurately to the measurement plane. Of course it's much more 
convenient to use the AIM when making broadband measurements.

> 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 believe it may be #52 - a newer version of #K. It "sits" between #31 
and #61.

> 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.

I wouldn't try to defend the power rating unless it was in some way 
qualified by a description of the CM environment

> 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.
Steve G3TXQ

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