Rule of Thumb for coax chokes
 

Based on some calculations I did today, I am offering
an original rule of thumb (as far as I know). Regarding
a coax choke, when deciding how many turns of coax to put
on a 2 liter pop bottle at two turns per inch, one needs
to avoid the self-resonant frequency. So don't put more
turns on the choke than the number of meters in a wavelength,
e.g. no more than 20 turns on 20m, no more than 6 turns on
6m. Backup calculations will be published on my web page.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Why avoid the self-resonant frequency?

That's the frequency at which the choking impedance is a maximum.
----
Reg

Rule of Thumb for coax chokes
 

Cec,

Suppose you havn't got a pop bottle but only a length of plastic drain
pipe of different diameter.

You will need a different rule of thumb for every contingency.
----
Reg.

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
Why avoid the self-resonant frequency?
That's the frequency at which the choking impedance is a maximum.

Personal preference - I would rather the choking impedance
be at maximum reactance rather than at maximum resistance.
I think that saves a little bit of power.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
Suppose you havn't got a pop bottle but only a length of plastic drain
pipe of different diameter.

Then I use my EXCEL spreadsheet which allows variation
in the number of turns per inch and diameter of the coil.
If you would like a copy, it can be downloaded from

http://www.qsl.net/w5dxp/Corum1.xls

You will need a different rule of thumb for every contingency.

2 liter pop bottles are in abundance in the US. If a coil
form is used for a coax choke, that's the most likely.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Cecil Moore wrote:
Reg Edwards wrote:

Suppose you havn't got a pop bottle but only a length of plastic drain
pipe of different diameter.


Then I use my EXCEL spreadsheet which allows variation
in the number of turns per inch and diameter of the coil.
If you would like a copy, it can be downloaded from

http://www.qsl.net/w5dxp/Corum1.xls

You will need a different rule of thumb for every contingency.


2 liter pop bottles are in abundance in the US. If a coil
form is used for a coax choke, that's the most likely.

But then you have to drink 2 liters of wet, sticky, gooey, sickeningly
sweet, soda pop.
73,
Tom Donaly, KA6RUH

Rule of Thumb for coax chokes
 

"Cecil Moore" wrote in message
. ..
Reg Edwards wrote:
Why avoid the self-resonant frequency?
That's the frequency at which the choking impedance is a maximum.

Personal preference - I would rather the choking impedance
be at maximum reactance rather than at maximum resistance.
I think that saves a little bit of power.
--
73, Cecil http://www.qsl.net/w5dxp
=====================================

But Cecil, maximum resistance, maximum reactance and maximum impedance
all occur at the same resonant frequency.

And at the resonant frequency minimum loss occurs in the choke anyway.
There's negligible loss of power in the choke left to save.
----
Reg.

Rule of Thumb for coax chokes
 

I like to drink soda water from 2l bottles with a splash of lemon
juice; sounding pretty good right now given that it's 97F in Maryland
and the weather this week is, as per the NWS, "Excessive Heat"

Dan


But then you have to drink 2 liters of wet, sticky, gooey, sickeningly
sweet, soda pop.
73,
Tom Donaly, KA6RUH

Rule of Thumb for coax chokes
 

Tom Donaly wrote:
2 liter pop bottles are in abundance in the US. If a coil
form is used for a coax choke, that's the most likely.

But then you have to drink 2 liters of wet, sticky, gooey, sickeningly
sweet, soda pop.

Lipton and Nestea tea also come in those bottles as does
lots of sugar free diet stuff.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
But Cecil, maximum resistance, maximum reactance and maximum impedance
all occur at the same resonant frequency.

Reg, if you would learn the Smith Chart, you would know
that is not true. :-) At self-resonance, the inductive
reactance cancels the capacitive reactance leaving a
pure resistance usually of a few thousand ohms. But I
agree with you that a purely resistive self-resonant
choke is not a bad thing.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

"Cecil Moore" wrote in message
...
Reg Edwards wrote:
But Cecil, maximum resistance, maximum reactance and maximum
impedance
all occur at the same resonant frequency.

Reg, if you would learn the Smith Chart, you would know
that is not true. :-) At self-resonance, the inductive
reactance cancels the capacitive reactance leaving a
pure resistance usually of a few thousand ohms. But I
agree with you that a purely resistive self-resonant
choke is not a bad thing.
--
73, Cecil http://www.qsl.net/w5dxp
======================================

Cec, I don't need a Smith Chart, and neither does anybody else, to
work out the resistance at resonance.

I don't think you quite know what you are doing with elementary
circuit analysis. The Smith Chart is giving you the wrong answer. The
resistance of a choke at HF at self resonance is in the order of a
megohm or more, not just a few thousand ohms.

By the way, what is the diameter and winding length of a USA pop
bottle.
----
Reg.

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
The
resistance of a choke at HF at self resonance is in the order of a
megohm or more, not just a few thousand ohms.

I just guessed at it, Reg, based on my measurements of
toroidal chokes and W2DU baluns.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
By the way, what is the diameter and winding length of a USA pop
bottle.

The diameter of a 2 liter bottle is 4 inches. The Bible
says the ratio of circumference to diameter of a circle
is 3. :-) The length of the bottle is about a foot.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

The diameter of a 2 liter bottle is 4 inches. The Bible
says the ratio of circumference to diameter of a circle
is 3. :-) The length of the bottle is about a foot.
--
73, Cecil http://www.qsl.net/w5dxp
============================================

Before publishing your rules of thumb you can check your reasoning by
using program SELFRES3. Download from website below.

I must admit, rules of thumb are quite adequate for coaxial chokes.
Almost anything will work. Very often things will work quite well
without a choke at all. ;o)
-----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Rule of Thumb for coax chokes
 

On Thu, 3 Aug 2006 03:37:05 +0100, "Reg Edwards"
wrote:

I must admit, rules of thumb are quite adequate for coaxial chokes.
Almost anything will work. Very often things will work quite well
without a choke at all. ;o)

But the Rule Of Thumb to avoid (presumably) parallel resonance of the
choke for the reasons given is ROT.

Owen
--

Rule of Thumb for coax chokes
 

Owen Duffy wrote:
On Thu, 3 Aug 2006 03:37:05 +0100, "Reg Edwards"
wrote:

I must admit, rules of thumb are quite adequate for coaxial chokes.
Almost anything will work. Very often things will work quite well
without a choke at all. ;o)

But the Rule Of Thumb to avoid (presumably) parallel resonance of the
choke for the reasons given is ROT.

Wouldn't the resonant circulating currents be at their
highest magnitudes at the parallel resonant point and
therefore the I^2*R losses in the coil be greater at
that frequency than on either side of self-resonance?
(I explained that avoiding self resonance is only a
personal preference.)
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

On Wed, 02 Aug 2006 21:17:04 GMT, "Tom Donaly"
wrote:

But then you have to drink 2 liters of wet, sticky, gooey, sickeningly
sweet, soda pop.
73,
Tom Donaly, KA6RUH

Or look in the nearest garbage can or dumpster. Of course, there are
two liter bottles of water as well. :)

--
73 for now
Buck
N4PGW

Rule of Thumb for coax chokes
 

Tom Donaly wrote:
Cecil Moore wrote:

Reg Edwards wrote:

2 liter pop bottles are in abundance in the US. If a coil
form is used for a coax choke, that's the most likely.


But then you have to drink 2 liters of wet, sticky, gooey, sickeningly
sweet, soda pop.
73,
Tom Donaly, KA6RUH

We get 'sparkling water' in 2l bottles because we like the fizzy feel to
our beverages. They also have club soda and soda water in 2l bottles.

Keep cool,
Galen, W8LNA

Rule of Thumb for coax chokes
 

Owen Duffy wrote:
But the Rule Of Thumb to avoid (presumably) parallel resonance of the
choke for the reasons given is ROT.

The self-resonance to be avoided is 1/2WL self-resonance,
e.g. 20 turns on 10m. I apologize for confusing the two
self-resonant concepts.
--
73, Cecil, http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

"Cecil Moore" wrote in message
.. .
Owen Duffy wrote:
On Thu, 3 Aug 2006 03:37:05 +0100, "Reg Edwards"
wrote:

I must admit, rules of thumb are quite adequate for coaxial chokes.
Almost anything will work. Very often things will work quite well
without a choke at all. ;o)

But the Rule Of Thumb to avoid (presumably) parallel resonance of the
choke for the reasons given is ROT.

Wouldn't the resonant circulating currents be at their
highest magnitudes at the parallel resonant point and
therefore the I^2*R losses in the coil be greater at
that frequency than on either side of self-resonance?
(I explained that avoiding self resonance is only a
personal preference.)
--
73, Cecil http://www.qsl.net/w5dxp

Hi Cecil

Doesnt the increase of impedance of the parallel resonant "balun"
discourage current from flowing into it? I considered that the source
impedance is constant and the "balun" impedance rises as resonance is
approached.
I figured the circulating current would be Q times the current thru it,
but the current thru it drops as its impedance rises.

If I'm wrong, I've been lucky so far.

Jerry

Rule of Thumb for coax chokes
 

"Cecil Moore" wrote

Wouldn't the resonant circulating currents be at their
highest magnitudes at the parallel resonant point and
therefore the I^2*R losses in the coil be greater at
that frequency than on either side of self-resonance?
(I explained that avoiding self resonance is only a
personal preference.)
======================================
Hi Cec,

The exceedingly small power loss in the choke depends on the impedance
of the power source which is driving it. It is a question of
non-conjugate mis-matching. But at self-resonance, and indeed
anywhere else, you can forget all about power loss. Especially as no
ferrite material is involved.

If you have bothered to check your "rule-of-thumb" and
"turns-per-metre-of-wavelength" against program SELFRES3, then,
provided results are in the same ball-park, all will be more than
satisfactory. SELFRES3 is itself only approximate. The choke's
self-resonant frequency is somewhat indeterminate as soon as anything
is connected to it.

A hank of a bunched number of turns is quite good enough as a coaxial
choke. It is only necessary to know the number of turns and the
diameter. Construction neatness helps with estimating the number of
turns but has hardly any effect on performance.

Coaxial chokes are a relatively unimportant circuit component.
Exactly what they are supposed to do is aways doubtful unless they are
used as baluns. I wonder why I am spending so much time discussing
the subject. Praps it's because I have nothing better to do.
smiley
----
Reg.

Rule of Thumb for coax chokes
 

Jerry Martes wrote:
Doesnt the increase of impedance of the parallel resonant "balun"
discourage current from flowing into it?

My bad for confusing 1/4WL self-resonance with 1/2WL
self-resonance. A choke is essentially non-functional
at the 1/2WL self-resonant point. That's the configuration
to be avoided.
--
73, Cecil, http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
A hank of a bunched number of turns is quite good enough as a coaxial
choke.

I got the 1/4WL and 1/2WL self-resonant points confused
in my mind. A "bunched number of turns" causing 1/2WL
self-resonance would function very poorly as a choke.
--
73, Cecil, http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Cecil,

A choke consists of an inductance in parallel with its stray
capacitance. It has only two terminals.

Its loss can be represented, either by a small resistance in series
with the inductance, or a very high resistance in shunt with the
inductance and its shunt stray capacitance.

What you mean by 1/4-wave and 1/2-wave resonance I have no idea and,
in any case, has nothing to do with how the extremely simple circuit
behaves.

The best thing to do is to forget the whole thing and find something
else of greater consequence to argue about. smiley
----
Reg.

Rule of Thumb for coax chokes
 

While you guys were chewing on this I decided to repair a broken coax
on the 80 meter array for beaming europe... Temp 96 degrees... Wind
blowing like snot with a storm front coming in and cumulus building to
the West and getting ready for a climax... I climb slowly to 100 feet
(puffing and sweating.. It can't be cause I'm out of shape! 'Must be
the heat', I mutter)...
After a bit of maneuvering, and using one foot to snag a drooping wire
I untangle the 70 feet of coax that had flopped back against the tower
and managed to wrap itself on everything in sight... I capture the
center insulator of the driven element that is waving widly in the
wind... After some ten minutes of stripping and clipping and clamping
I have the coax reattached... I drag out the propane soldering
pencil... I can't keep it lit in the wind... I even resort to lighting
it inside my tool pouch.. All I succeed in doing is burning a hole in
the pouch... Jeez Louise... I give up and climb down... I left the
connected parts taped to the tower leg... I'll have to solder on a
calmer day... The saving grace is that I don't have a coaxial choke to
deal with...

denny

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
What you mean by 1/4-wave and 1/2-wave resonance I have no idea and,
in any case, has nothing to do with how the extremely simple circuit
behaves.

The circuit is extremely simple only in the human mind, Reg.
It's not so simple in reality. Given a real world choke
wound out of coax, as one increases the frequency of the
signal generator, one will encounter resonances. Some will
look like parallel resonances and some will look like serial
resonances. The first resonance is the 1/4WL self-resonance.
--
73, Cecil, http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Cec,

Can't you see that the first resonance corresponds to the parallel
resonance of the inductance with its stray capacitance, and is what
you call its 1/2-wave resonance?

At your 1/2-wave resonance the input impedance is very high regardless
of what the load impedance is on the other side. It does not behave
anything like a transmission line.

Higher frequency resonances, IF they exist, will be above and outside
the amateur bands and of no interest to anybody.

Interest lies only in either side of the first resonance. That is in
the wide band of frequencies at which the impedance is greater than
1000 ohms or so.

See program SELFRES3.
----
Reg.

Rule of Thumb for coax chokes
 

Cecil Moore wrote:
Based on some calculations I did today, I am offering
an original rule of thumb (as far as I know). Regarding
a coax choke, when deciding how many turns of coax to put
on a 2 liter pop bottle at two turns per inch, one needs
to avoid the self-resonant frequency. So don't put more
turns on the choke than the number of meters in a wavelength,
e.g. no more than 20 turns on 20m, no more than 6 turns on
6m. Backup calculations will be published on my web page.
--
73, Cecil http://www.qsl.net/w5dxp

20 Turns is way too much for 20 through to 10.

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

Some actual measurements with a Network Analyzer. It shows 6 turns is
enough for 20 through to 10.

Rule of Thumb for coax chokes
 

I have just improved and added to the notes to program SELFRES3.

The issue date on the first page of operating notes has been changed
to 4th August 2006.

I suggest you download SELFRES3 again and use it overwrite your old
copies.
-----
.................................................. ..........
Regards from Reg, G4FGQ
For Free Radio Design Software go to
http://www.btinternet.com/~g4fgq.regp
.................................................. ..........

Rule of Thumb for coax chokes
 

That is neet. Now I just got to figure a choke of RG8X at 146mhz to
keep the RF from comming back down the outside of the coax cable from
the J pole.
The VSWR is realy good at 1:1.1, and it talks realy well.

What about ferrite beads/chokes over the coax instead of the coil of
coax cable?

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
Can't you see that the first resonance corresponds to the parallel
resonance of the inductance with its stray capacitance, and is what
you call its 1/2-wave resonance?

It may just be semantics. I call the first parallel self-
resonant point the *1/4WL* self-resonant point. At its self-
resonant frequency, a mobile loading coil is 1/4WL long. I
am using that same convention for the coax choke. For instance,
my 75m bugcatcher mobile loading coil is self-resonant at
~6.6 MHz. That's the frequency at which it is 1/4 wavelength
long and presents a high impedance. At some higher frequency,
it is 1/2WL long and presents a low impedance.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Bindy wrote:
Cecil Moore wrote:
Based on some calculations I did today, I am offering
an original rule of thumb (as far as I know). Regarding
a coax choke, when deciding how many turns of coax to put
on a 2 liter pop bottle at two turns per inch, one needs
to avoid the self-resonant frequency. So don't put more
turns on the choke than the number of meters in a wavelength,
e.g. no more than 20 turns on 20m, no more than 6 turns on
6m. Backup calculations will be published on my web page.

20 Turns is way too much for 20 through to 10.

I didn't say anything about "20 through to 10". Here's what
my rule of thumb says:

No more than 20 turns on 20m, no more than 10 turns on 10m,
and no more than 6 turns on 6m.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Will wrote:
That is neet. Now I just got to figure a choke of RG8X at 146mhz to
keep the RF from comming back down the outside of the coax cable from
the J pole.

My rule of thumb is for RG-213 wrapped around a 4" dia.
2L pop bottle and thus applies mostly to HF. Using a 2"
dia. coil form (pill bottle) with RG8X, my EXCEL
program says 2-3 turns is about right for 2m.

What about ferrite beads/chokes over the coax instead of the coil of
coax cable?

That works. Just make sure the ferrite is functional at
146 MHz, maybe #67 material.
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

"Cecil Moore" wrote in message
. ..
Bindy wrote:
Cecil Moore wrote:
Based on some calculations I did today, I am offering
an original rule of thumb (as far as I know). Regarding
a coax choke, when deciding how many turns of coax to put
on a 2 liter pop bottle at two turns per inch, one needs
to avoid the self-resonant frequency. So don't put more
turns on the choke than the number of meters in a wavelength,
e.g. no more than 20 turns on 20m, no more than 6 turns on
6m. Backup calculations will be published on my web page.

20 Turns is way too much for 20 through to 10.

I didn't say anything about "20 through to 10". Here's what
my rule of thumb says:

No more than 20 turns on 20m, no more than 10 turns on 10m,
and no more than 6 turns on 6m.
======================================
Cec,

Does all the above apply to the diameter of a pop bottle?

And what is the diameter over the plastic jacket of the coax?

The length of the coil will be N times the jacket diameter, assuming
the N turns are close-spaced.

Don't forget, mean coil diameter will be pop bottle diameter plus coax
jacket diameter. It does make a difference.
-----
Reg.

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
Does all the above apply to the diameter of a pop bottle?

Yes 4" dia. and 2 turns per inch using RG-213.

And what is the diameter over the plastic jacket of the coax?

0.405" for RG-213, approximately 1/2".

The length of the coil will be N times the jacket diameter, assuming
the N turns are close-spaced.

Yes, that's why there are 2 turns per inch for RG-213.

Don't forget, mean coil diameter will be pop bottle diameter plus coax
jacket diameter. It does make a difference.

Maybe a 10-20% difference. Doesn't make much difference to a
rule of thumb. :-)
--
73, Cecil http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

"Will" wrote in message
oups.com...
That is neet. Now I just got to figure a choke of RG8X at 146mhz to
keep the RF from comming back down the outside of the coax cable from
the J pole.
The VSWR is realy good at 1:1.1, and it talks realy well.

What about ferrite beads/chokes over the coax instead of the coil of
coax cable?


Hi Will

I have been using some affordable ferrites for "keeping the RF from the
outside of the coax" at about 2 meters. All my crude measurements indicate
that the Very affordable ferrite tubes from All Electronics
http://www.allelectronics.com/ work OK. I figured the tubes were intended
to keep RFI from conducting down the cables inside the *All ferrite tubes*,
so I tried them, and they work for me. They have some snap-on models that
might have an ID big enough to fit over your RG8X.

Jerry

Rule of Thumb for coax chokes
 

Cec,

Let us know when your rule-of-thumb is available from your website.
I'm looking forward to seeing the details.

I guess there will be the usual collection of over-meticulous
nit-pickers.
----
Reg.

Rule of Thumb for coax chokes
 

Reg Edwards wrote:
Let us know when your rule-of-thumb is available from your website.
I'm looking forward to seeing the details.

It's at http://www.qsl.net/w5dxp/Corum1.xls

Can you run EXCEL, Reg, or do you need it in a different form?
--
73, Cecil, http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Cec, I can't run Excel.

I need something which will run just by clicking on it.
----
Reg.
==============================


"Cecil Moore" wrote in message
...
Reg Edwards wrote:
Let us know when your rule-of-thumb is available from your
website.
I'm looking forward to seeing the details.

It's at http://www.qsl.net/w5dxp/Corum1.xls

Can you run EXCEL, Reg, or do you need it in a different form?
--
73, Cecil, http://www.qsl.net/w5dxp

Rule of Thumb for coax chokes
 

Will wrote:
That is neet. Now I just got to figure a choke of RG8X at 146mhz to
keep the RF from comming back down the outside of the coax cable from
the J pole.
The VSWR is realy good at 1:1.1, and it talks realy well.

What about ferrite beads/chokes over the coax instead of the coil of
coax cable?

Digikey carries a pretty broad line of Steward long form ferrite bead
cores. You can check the specifications at http://www.steward.com/

For instance, core HFB143064-300 has an impedance of about 180 ohms at
146 MHz. Type HF is their highest frequency material.

Core 28B0562-200 (same size in the lower frequency, 28 material)
produces an impedance of about 360 ohms per core.

I think both of these would fit over RG8X and are about an inch and an
eighth long.