Ian White GM3SEK wrote:
In the chokes we're looking at, the low-impedance series resonances of
which Cecil complains do not occur below 30MHz. Those resonances exist,
but not on the HF frequencies where the chokes would actually be used.

But, Ian, what about 75m and 40m?

Those resonances above 26 MHz are transmission line effects.
The largest coil is only 12 turns, not nearly enough for 75m
operation. The largest 12 turn coil has a choking impedance
of only 100 ohms on 75m. Scale the choke to 75m and 40-50 turns
are probably required. That would certainly lower the 1/2WL
resonant frequencies into the HF ham bands.

The 12 turn coil's peak impedance is around 15 MHz and its
1/2WL low impedance response is around 31 MHz. If we scale
the peak impedance value to 4 MHz by increasing the turns,
the 1/2WL low impedance response would be around 8 MHz. Such
a choke would be useless above 10 MHz.

Bottom Line: If enough turns are used to achieve a high choking
impedance on 75m, the 1/2WL resonant transmission line effects
will occur in the middle of HF making it useless on the higher
HF frequencies.

Within the practical working frequency range of all of these coiled-coax
chokes, the performance can be accurately described as that of a simple
parallel tuned LC circuit, which displays no transmission-line behaviour
whatever.

This is obviously a false statement proved by your own graphs.
If there were no transmission line effects, the phase graphs
would all converge on -90 degrees. All of the phase bumps above
26 MHz are transmission line effects. If the chokes had their
maximum impedance at 4 MHz, those 1/2WL transmission line effects
would probably be in the range of 10 MHz rendering them useless
on 30m-10m.

Cecil complains that
One might say it is misbehaving and is a very poor design.

That sounds to me like the complaint of someone who has a pet theory to
hammer, and is disappointed when he can't find a nail.

Actually, I was just quoting this web page:

http://www.k1ttt.net/technote/airbalun.html

"- Don't bunch the turns together. Wind them as a single
layer on a form. Bunching the turns kills the choking effect
at higher frequencies." I agree with WA2SRQ that the bunched
coil choke is a poor design. Do you think that WA2SRQ has a
pet theory?

I think that's it, really. The graphs themselves say the rest.

They certainly do. Everything above 26 MHz is obviously transmission
line effects. If the chokes were designed for the lower part
of the HF spectrum, the 1/2WL low impedance points, caused by
the transmission line effects, would be in the middle of the HF
spectrum.

Scale the high impedance points for 75m and the low impedance
bumps due to transmission line effects will occur in the
middle of HF.
--
73, Cecil http://www.w5dxp.com