Jim,
This sketch may help:
http://www.karinya.net/g3txq/temp/4%20to%201%20current%20balun%202.png
I've re-drawn the usual 4:1 current balun schematic (Fig 1) into a
different, but exact equivalent, schematic Fig 2. It's clear that the
input differential-mode voltage _must_ appear across the two balun
windings P2 & P1 in a way that doesn't happen in a 1:1 current balun,
and that "voltage transformer" action must occur in B1 & B2 to drive
voltages across S2 & S1.
Please note: I'm _not_ saying it's a voltage balun - it's easy to show
that it drives equal _currents_ into the two output legs; but there _is_
"voltage transformer" action happening within one or both cores in a way
that doesn't happen with the 1:1.
73,
Steve G3TXQ
Steve Hunt wrote:
> Kevin,
>
> I'll risk further criticism of AIM measurements and point you to some
> charts on my web site which might make things clearer:
>
> http://www.karinya.net/g3txq/chokes/
>
> Notice how narrow-band the resistive portions (black bands) are of the
> #61 designs, and bear in mind the earlier discussion about SRF
> measurement uncertainty with narrow-band chokes, and you can see that
> #31 or #43 material is a much safer option.
>
> 73,
> Steve G3TXQ
>
>
>
> Kevin Normoyle wrote:
>
>> This is all great and thanks for taking the time to go thru it yet one
>> more time.
>> Even though I've read the papers, it's great to see the give and take of
>> slightly different points of view for really getting a grip on what all
>> the key issues are.
>>
>> So looking at Fair Rite #61, 13 turns on 2.4" o.d core, seems primarily
>> resistive above 14Mhz.
>>
>> Assuming I'm just thinking about the 20M/15M/10M bands, 13 turns of
>> RG303 on a double stack of #61 seems to meet the desired goals?
>>
>> Am I wrong there?
>>
>> But then, if our measurement capabilities are better for below 14mhz,
>> and I can be confident of the inductive reactance I get from #61 at the
>> lower frequencies (and knowing whether there are resonances there)...why
>> can't the same double stack be good for <14 mhz?
>>
>> I guess I'm wondering if the justification for "resistive impedance is
>> better" is being taken from one frequency range and being applied to all
>> frequency ranges...unnecessarily implying #43 (or #31) is better than #61
>>
>> ?? I may just be trying to summarize something that can't be summarized.
>>
>> Seems like some of the issue is trying to have one thing cover the range
>> of 1-30mhz which is too hard. And our inability to measure well, for
>> over 10mhz.
>>
>> I also can't help but think that using more turns of narrower RG303 thru
>> a core is better for controlling stray capacitance, therefore creating
>> more repeatable results...especially important if I know I can't trust
>> the measurements of what I build.
>> ???
>> -kevin
>> AD6Z
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