Cecil Moore wrote:
Ian White GM3SEK wrote:
Across the whole 1-30MHz band, the bunched choke behaves as an almost
perfect L-C circuit, free from any unwanted resonances.

One additional point. If the above were true, as the
frequency is increased, the phase angle of the coiled
choke impedance would drop from ~90 degrees to zero at
the self-resonant frequency, and then rise back to ~-90
degrees and stay there. But that's not what happens.

In every single case, the phase angle rises toward -90
degrees *and then decreases* as the 1/2WL self-resonance
point is approached. That is a clear indication of transmission
line effects. A lumped circuit simply doesn't act that way.

The spreadsheet at
http://www.ifwtech.co.uk/g3sek/misc/chokes.xls
now includes graphs of the phase information for all the chokes.

[ Thank you, Owen - the phase axis label is now fixed .
For anyone interested who doesn't have Excel, Microsoft's free Excel
file viewer is at http://tinyurl.com/cup85 ]

Coming all the way back to the original question, the data confirms that
even though it may look like something held together with duct tape, a
coiled coax choke can be an excellent single-band solution. At its
parallel self-resonant frequency, it will have a much higher common-mode
impedance than a generic string of ferrite beads. It can probably
outperform or at least equal a ferrite choke over two or possibly three
adjacent HF bands; but being a resonant device, it cannot deliver
extreme broadband performance.

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.

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. 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.

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


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

On Sun, 22 Oct 2006 23:56:04 +0100, Ian White GM3SEK
wrote:

[ Thank you, Owen - the phase axis label is now fixed .
For anyone interested who doesn't have Excel, Microsoft's free Excel
file viewer is at http://tinyurl.com/cup85 ]

Hi Owen,

It is far easier to simply use OpenOffice which is an executable that
will translate to/from Windows Office (any spread sheet, document,
presentation, drawing...). The Open Document format is the mandated
standard of the European Community, if I recall correctly.

73's
Richard Clark, KB7QHC

On Sun, 22 Oct 2006 16:24:33 -0700, Richard Clark
wrote:

Hi Owen,

Sorry Ian, wrong side of the continental divide here.

On Sun, 22 Oct 2006 16:24:33 -0700, Richard Clark
wrote:

Hi Owen,

It is far easier to simply use OpenOffice which is an executable that
will translate to/from Windows Office (any spread sheet, document,
presentation, drawing...). The Open Document format is the mandated
standard of the European Community, if I recall correctly.

Be careful. If any VB type macros are included in Excel Open Office
will barf. Been there done that.

Danny, K6MHE

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Danny Richardson wrote:
On Sun, 22 Oct 2006 16:24:33 -0700, Richard Clark
wrote:

Hi Owen,

It is far easier to simply use OpenOffice which is an executable that
will translate to/from Windows Office (any spread sheet, document,
presentation, drawing...). The Open Document format is the mandated
standard of the European Community, if I recall correctly.

Be careful. If any VB type macros are included in Excel Open Office
will barf. Been there done that.

Danny, K6MHE



Opens fine in OpenOffice 2 on SUSE 10 but I did have to reposition
the graphs which were over the table.

Charlie.

- --
www.wymsey.co.uk
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Version: GnuPG v1.4.2 (GNU/Linux)
Comment: Using GnuPG with SUSE - http://enigmail.mozdev.org

iD8DBQFFPIKufhKqaKFAJ/YRAgnOAJ9ZjDMfv6s+TwcswZd0YbJQJK5e1QCcCskT
Dbm7fF6MOISjjCsbzjBLihA=
=zEFh
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charlie wrote:
Danny Richardson wrote:
On Sun, 22 Oct 2006 16:24:33 -0700, Richard Clark
wrote:

Hi Owen,

It is far easier to simply use OpenOffice which is an executable that
will translate to/from Windows Office (any spread sheet, document,
presentation, drawing...). The Open Document format is the mandated
standard of the European Community, if I recall correctly.

Be careful. If any VB type macros are included in Excel Open Office
will barf. Been there done that.

Danny, K6MHE



Opens fine in OpenOffice 2 on SUSE 10

Thanks for that information, Charlie - it's very useful to know what
other systems can see.

but I did have to reposition
the graphs which were over the table.

That's how I saved the graphs, so OpenOffice got those layout details
right.

Once the graphs have been plotted, it isn't necessary to look at the
underlying table very often, because the data can be seen in a popup
window by running the mouse pointer along each plotted line. If
OpenOffice can do that too, you may find it a convenient feature.

Alternatively, you could drag both graphs away to the right, and then
use the horizontal scroll bar to move between the table and graphs.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

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

Cecil Moore wrote:
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.

Sorry for the delay in replying, but I just did something completely
radical for this type of discussion: hauled out some cable, made some
chokes, and measured them.

These chokes were intended to be like the ones recommended in the ARRL
Handbook for 3.5MHz and for 7MHzz, both using 22ft of RG213. What I had
was actually 21ft, and this length was wound into a flat coil having
various numbers of turns. The choking impedances and phase angles were
measured on an N2PK Vector Network Analyser.

Ten turns made a choke that had 1000 ohms impedance from 3.4MHz to
6.4MHz, falling to about 650 ohms by 7.3MHz. This makes a respectable
two-band choke, if you judge it by the criterion of needing about 500
ohms minimum impedance, but it's a stretch to cover both bands from edge
to edge (9 turns was probably a slightly better compromise). Moreover
the maximum impedance of 17k is "wasted" between the amateur bands at
4.6MHz.

That confirms our shared suspicion that the Handbook's claim of "a
broad resonance that easily (sic) covers three octaves" is
over-optimistic. Where the coiled-cable choke really excels is as a
single-band device, exploiting its extremely high peak impedance at
parallel resonance.

Without needing to change the overall length of cable, the peak
resonance can be shifted to different frequencies by increasing or
decreasing the number of turns, although I couldn't persuade 21ft below
4.6MHz (10 turns) because the bending radius was becoming too small for
RG213.

However, it's perfectly clear that Cecil's estimate of "40-50 turns"
needed for a 75m choke is way off.

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.

Right conclusion about the choke being useless a long way above its peak
resonance - but not the right reason for it. The true reason is the very
simple property of a parallel LC circuit (the inductance of the coil,
resonated by its own self-capacitance) which means that far above
resonance its parallel impedance drops to a very low value. That's what
makes it useless at those frequencies.

The 4.6MHz choke does have series resonances at about 23MHz 33MHz ,but
those cannot be said to affect the performance of the choke in any
practical way, because the choke doesn't have any usable performance at
these frequencies anyway.


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 keeps resolutely ignoring the reservation: "within the practical
working range of the choke".

Within the frequency range where the choke has a practically useful
value of impedance, there are no - repeat NO - signs of transmission
line effects. Its behaviour is purely LC, its own inductance resonating
with its self-capacitance.


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 WA2SRQ's advice is one-sided, because it fails to recognize the
benefit of bunching the cable together - namely that it moves the whole
resonance curve downward (due to the increased self-capacitance) without
needing to increase the length of cable. For someone who wants a
low-band choke, that is a Very Good Thing. The poorer performance at
higher frequencies is the obvious natural tradeoff for having moved the
whole resonance curve downward - but that doesn't make it a "poor
design".

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.

Hands-on measurements prove otherwise - the spurious resonances stay
pretty much where they were, above 20MHz.

As stated above, I measured a choke which is resonant at 4.6MHz. It has
over 1000 ohms impedance at 3.5MHz, rising to over 2k at 4MHz, so it
would be a very good performer on both 75m and 80m.

But above the main parallel resonance there are no bumps in the
impedance or ripples in the phase response at any frequency below 20MHz
- none.

It is ridiculous for Cecil to describe such a choke as "misbehaving and
a very poor design". On the contrary, bunching the turns to increase the
self-capacitance has proved a very good way of moving the main resonance
downward to make an effective single-band choke for 75/80m, while
leaving all the unwanted resonances parked above 20MHz.


--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian White GM3SEK wrote:
However, it's perfectly clear that Cecil's estimate of "40-50 turns"
needed for a 75m choke is way off.

Wouldn't you say the number of turns depends upon the
diameter of the coil? How many turns would be needed
for 75m self-resonance if one were using RG-58 wound
on a 3 inch diameter PVC pipe?

Using the inductance formula in the ARRL Handbook,
40 turns on a 3 inch diameter form at 4 TPI is
about 32 uH or about 800 ohms on 4 MHz. The
distributed capacitance would lower it even farther.
40 turns on a 3" form would be an absolute minimum
for any high SWR situation on 75m.

Right conclusion about the choke being useless a long way above its peak
resonance - but not the right reason for it. The true reason is the very
simple property of a parallel LC circuit (the inductance of the coil,
resonated by its own self-capacitance) which means that far above
resonance its parallel impedance drops to a very low value. That's what
makes it useless at those frequencies.

Ian, your own graphs show transmission line effects. The fact
that the phase angle does NOT go to -90 degrees and stay there
proves those are transmission line effects. Here's what the
IEEE paper says:

"The concept of coil 'self-capacitance' is an attempt to
circumvent transmission line effects on small coils when the
current distribution begins to depart from its DC behavior."

"There are a great number of formulae for coil self-capacitance.
None are of particular value for quarter-wave helical resonators
anywhere near the 90 degree point."

Your parallel self-resonance *IS* the 90 degree point. I wish
you would take time out to realize that if there were no
transmission line effects, the phase angle would go to -90
degrees and stay there. Please set up a parallel inductor
and capacitor and see for yourself what happens as one
increases the frequency past parallel resonance. The phase
angle is asymptotic to -90 degrees.

The 4.6MHz choke does have series resonances at about 23MHz 33MHz ,but
those cannot be said to affect the performance of the choke in any
practical way, because the choke doesn't have any usable performance at
these frequencies anyway.

Those grapes were probably sour anyway. :-) Ian, a lumped
circuit inductor and parallel capacitance would NOT have
those series resonances. A lumped circuit would go to a
phase angle of -90 degrees and stay there while the impedance
drops inversely proportional to frequency. Seems to me, you have
just admitted that the chokes you wound are exhibiting transmission
line effects just as I predicted. (Except for the VF error I made.)

THE CHOKE DOESN'T HAVE ANY USABLE PERFORMANCE AT THOSE HIGHER
FREQUENCIES *BECAUSE* OF THE TRANSMISSION LINE EFFECTS!!!

Cecil keeps resolutely ignoring the reservation: "within the practical
working range of the choke".

That's circular logic, Ian. I said that series resonant
transmission line effects limit the practical working range of
a coax choke and you disagreed. Now you have proved I am
right with your own measurements on chokes of your own design.

If those actually were lumped inductors and capacitors as you
continue to assert, THE SERIES RESONANCES THAT YOU MEASURED
WOULD NOT AND COULD NOT EXIST!!!

The series resonant transmission line effects are the *CAUSE*
of the practical working range of the choke being limited.

In a parallel LC circuit, as the frequency increases, the
capacitive reactance becomes dominant and decreases inversely
proportional to frequency. The phase angle would be asymptotic
to -90 degrees. None of the measurements look anything like that.
All of the measurements exhibit transmission line effects.

Within the frequency range where the choke has a practically useful
value of impedance, there are no - repeat NO - signs of transmission
line effects. Its behaviour is purely LC, its own inductance resonating
with its self-capacitance.

This will be the forth time I have said this, Ian. If there were
no sign of transmission line effects, the phase angle would go to
-90 degrees and stay there. If the phase angle doesn't go to -90
degrees and stay there, that is *prima facie evidence* of transmission
line effects. Lumped parallel inductors and capacitors don't exhibit
the effects measured by you on the chokes that you wound.

Scale the high impedance points for 75m and the low impedance
bumps due to transmission line effects will occur in the
middle of HF.

Hands-on measurements prove otherwise - the spurious resonances stay
pretty much where they were, above 20MHz.

Uhhhhh Ian, 20 MHz *IS* HF! The transmission line 1/2WL series
resonant effects are occurring in the HF range! That's why the
75m choke doesn't work on 15m!!! 20-30 MHz is 37% of HF.

As stated above, I measured a choke which is resonant at 4.6MHz. It has
over 1000 ohms impedance at 3.5MHz, rising to over 2k at 4MHz, so it
would be a very good performer on both 75m and 80m.

But it wouldn't make a good performer on 15m because of the
series resonant transmission line effects. That was my point
from the beginning. (The mistake I made was forgetting that the
VF of the choke changes with frequency.)

It is ridiculous for Cecil to describe such a choke as "misbehaving and
a very poor design".

This thread has not been about single-band or narrow-band chokes.
We were talking about broadband chokes being able to cover three
octaves of HF. The bunched coil choke is much more narrow-banded
than helical wound chokes thus rendering them virtually useless
for broadband operation. They *misbehave* in broadband (all-HF)
applications. They are a *very poor design* for broadband (all-HF)
applications.
--
73, Cecil http://www.w5dxp.com

Cecil Moore wrote:
Ian White GM3SEK wrote:
However, it's perfectly clear that Cecil's estimate of "40-50 turns"
needed for a 75m choke is way off.

Wouldn't you say the number of turns depends upon the
diameter of the coil? How many turns would be needed
for 75m self-resonance if one were using RG-58 wound
on a 3 inch diameter PVC pipe?

Using the inductance formula in the ARRL Handbook,
40 turns on a 3 inch diameter form at 4 TPI is
about 32 uH or about 800 ohms on 4 MHz. The
distributed capacitance would lower it even farther.
40 turns on a 3" form would be an absolute minimum
for any high SWR situation on 75m.


I am not your offshore lab service, Cecil. If you want to back up your
speculations, do your own work.

Right conclusion about the choke being useless a long way above its
peak resonance - but not the right reason for it. The true reason is
the very simple property of a parallel LC circuit (the inductance of
the coil, resonated by its own self-capacitance) which means that far
above resonance its parallel impedance drops to a very low value.
That's what makes it useless at those frequencies.

Ian, your own graphs show transmission line effects. The fact
that the phase angle does NOT go to -90 degrees and stay there
proves those are transmission line effects. Here's what the
IEEE paper says:

"The concept of coil 'self-capacitance' is an attempt to
circumvent transmission line effects on small coils when the
current distribution begins to depart from its DC behavior."

"There are a great number of formulae for coil self-capacitance.
None are of particular value for quarter-wave helical resonators
anywhere near the 90 degree point."


This discussion doesn't involve anybody's formula for self-capacitance.
The coil resonates using whatever value of self-capacitance it has in
reality.

Your parallel self-resonance *IS* the 90 degree point. I wish
you would take time out to realize that if there were no
transmission line effects, the phase angle would go to -90
degrees and stay there. Please set up a parallel inductor
and capacitor and see for yourself what happens as one
increases the frequency past parallel resonance. The phase
angle is asymptotic to -90 degrees.

I know what a parallel LC circuit does. The point you continue to evade
is that, from VLF up to about 20MHz, this coil of cable behaves in
exactly the same way.

The circuit looks inductive below the resonant frequency and capacitive
above it, and passing through resonance the phase angle of the
impedance flips from +90deg to -90deg... and then it stays very close to
90deg, clear up to about 20MHz. (The VNA reports angles of -88 to
-89deg.)


The 4.6MHz choke does have series resonances at about 23MHz 33MHz
,but those cannot be said to affect the performance of the choke in
any practical way, because the choke doesn't have any usable
performance at these frequencies anyway.

Those grapes were probably sour anyway. :-) Ian, a lumped
circuit inductor and parallel capacitance would NOT have
those series resonances. A lumped circuit would go to a
phase angle of -90 degrees and stay there while the impedance
drops inversely proportional to frequency. Seems to me, you have
just admitted that the chokes you wound are exhibiting transmission
line effects just as I predicted. (Except for the VF error I made.)

THE CHOKE DOESN'T HAVE ANY USABLE PERFORMANCE AT THOSE HIGHER
FREQUENCIES *BECAUSE* OF THE TRANSMISSION LINE EFFECTS!!!

Cecil keeps resolutely ignoring the reservation: "within the
practical working range of the choke".

That's circular logic, Ian. I said that series resonant
transmission line effects limit the practical working range of
a coax choke and you disagreed. Now you have proved I am
right with your own measurements on chokes of your own design.

If those actually were lumped inductors and capacitors as you
continue to assert, THE SERIES RESONANCES THAT YOU MEASURED
WOULD NOT AND COULD NOT EXIST!!!


That is the usual mixture of selective quoting and false logic. What
you continue to overlook is that the behaviour all the way from DC
through the 4.7MHz resonance and onward up to about 20MHz can be
accurately represented by nothing more elaborate than a simple LCR
circuit. The fall in impedance from the resonant frequency up to about
20MHz is completely accounted for by just those three simple parameters:
two reactances and one fixed loss resistance in parallel.

Above that frequency there are effects that the simple LCR model cannot
account for. I have always said so, and yes, a transmission-line model
could account for those.

The series resonant transmission line effects are the *CAUSE*
of the practical working range of the choke being limited.

That is simply not true. The limitation in working range is simply the
shunting effect of the self-capacitance, which becomes increasingly
important above resonance and causes a long progressive fall in
impedance. This effect is very simple and entirely predictable. By 20MHz
it has reduced the impedance to a hundred ohms or less, which means that
the coil of cable is no use as a feedline choke for that frequency.

The series resonances above 20MHz cause further dips in impedance to
only a few ohms, but those dips are quite localized in frequency. They
are not the cause of the long progressive fall in impedance above the
parallel resonance, which is what limits the usable bandwidth of the
choke.

The challenge is still on the table, Cecil, for YOU to develop a
quantified transmission-line model that will predict all the measured
properties of a resonant choke over that wider range of frequencies.

The rest is snipped, because it's just you continuing your own argument
with the straw-man you have manufactured. A self-resonant choke is not
a wideband solution capable of cover the whole of HF. I never expected
it to be, and never claimed it would be, so stop acting as if I had.



--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek