Isolation of guy wires
 

Has anyone thought of trying to use some of the ferrite beads to isolate the
guy wires of a tower for RF so the tower could be shunt fed ? Along the same
lines could the beads be used to electrically brake up the wires into non
resonate lengths ?

Isolation of guy wires
 

Ralph Mowery wrote:
Has anyone thought of trying to use some of the ferrite beads to isolate the
guy wires of a tower for RF so the tower could be shunt fed ? Along the same
lines could the beads be used to electrically brake up the wires into non
resonate lengths ?

The most effective ferrites are primarily resistive
thus dissipating some power. Maybe a more reactive
ferrite might work better?
--
73, Cecil http://www.w5dxp.com

Isolation of guy wires
 

"Ralph Mowery" ha scritto nel messaggio
link.net...
Has anyone thought of trying to use some of the ferrite beads to isolate the
guy wires of a tower for RF so the tower could be shunt fed ? Along the same
lines could the beads be used to electrically brake up the wires into non
resonate lengths ?

The inductance of a piece of wire passing through a ferrite bead would be way
too low to produce a discernible choking effect at HF frequencies.

73

Tony I0JX

Isolation of guy wires
 

Antonio Vernucci wrote:
The inductance of a piece of wire passing through a ferrite bead would
be way too low to produce a discernible choking effect at HF frequencies.

Ever heard of a w2du balun? http://w2du.com/r3ch21a.pdf
How about passing the wire through 50 #77 beads as
recommended by the ARRL Antenna Book?
--
73, Cecil http://www.w5dxp.com

Isolation of guy wires
 

Ralph Mowery wrote:
Has anyone thought of trying to use some of the ferrite beads to isolate the
guy wires of a tower for RF so the tower could be shunt fed ? Along the same
lines could the beads be used to electrically brake up the wires into non
resonate lengths ?

It would require multiple beads at each point, and at multiple points.
While it could be made to work, it would be heavy and expensive. That's
why egg insulators or non-conductive guys are used instead.

Roy Lewallen, W7EL

Isolation of guy wires
 

Roy Lewallen wrote:
Ralph Mowery wrote:

Has anyone thought of trying to use some of the ferrite beads to
isolate the guy wires of a tower for RF so the tower could be shunt
fed ? Along the same lines could the beads be used to electrically
brake up the wires into non resonate lengths ?


It would require multiple beads at each point, and at multiple points.
While it could be made to work, it would be heavy and expensive. That's
why egg insulators or non-conductive guys are used instead.

However, such things have been done for stuff like the electrical power
drop to your house.


I believe Jim Brown's website has a picture of where he's got a bunch of
clamp on ferrites on the feeder for this sort of purpose (because,
obviously, a insulator wouldn't work)
Check figure 31 on page 23 of http://audiosystemsgroup.com/RFI-Ham.pdf



Roy Lewallen, W7EL

Isolation of guy wires
 

On Fri, 09 Mar 2007 12:56:12 -0800, Roy Lewallen wrote:

Ralph Mowery wrote:
Has anyone thought of trying to use some of the ferrite beads to isolate the
guy wires of a tower for RF so the tower could be shunt fed ? Along the same
lines could the beads be used to electrically brake up the wires into non
resonate lengths ?

It would require multiple beads at each point, and at multiple points.
While it could be made to work, it would be heavy and expensive. That's
why egg insulators or non-conductive guys are used instead.

Roy Lewallen, W7EL

Yes Ralph, beads could be used to achieve what you want. I refer you to a paper
that will appear in Reflections 3 as Chapter 21A, which is a continuation of
Chapter 21 in Reflections 1 and 2. Chapter 21 tells of the need for a balun, and
how the beads perform as a balun.

However, Chapter 21A describes how I developed the idea for using beads for the
W2DU balun. The idea came as a spin-off from a method I used during
radiation-pattern measurements for the antennas that flew on TIROS weather
satellites. The downlead for the signal received from the antennas on the
satellite was reradiating EM energy, and distorting the radiation patterns. I
reasoned that placing a bead every quarterwavelength along the downlead would
breakup the current on the lead, which it did. I then transformed the idea into
the W2DU balun, which is described in all editions of the ARRL Handbook since
around 1985. Chapter 21 is a repeat of my article in QST for March 1983.

Chapters 21 and 21A can be found for downloading on my web page at www.w2du.com.
Click separately on 'View Chapters from Reflections 2' for Chapter 21, and click
on 'Preview Chapters from Reflections 3' for Chapter 21A.

Hope this helps.

Walt, W2DU

Isolation of guy wires
 

It would require multiple beads at each point, and at multiple points. While
it could be made to work, it would be heavy and expensive. That's why egg
insulators or non-conductive guys are used instead.

While in a balun a reactance of say 1000 ohm would be more than adequate for the
purpose of avoiding radiation (or reception) by common-mode currents, in the
proposed application (guy-wires) a much higher reactance would be required. As
a matter of fact at the top of the tower, where there is a voltage peak, the
impedance is very high, and the guy-wire insulator (either an egg or ferrite
beads) should then show a very high reactance value (probably in the region of
tens of thousands of ohm) not to disturb the antenna.

I never played with ferrite beads, but I have a rather strong feeling that such
high reactance values are hard to obtain at 3.5 MHz just using beads.

73

Tony I0JX

Isolation of guy wires
 

Actually, you can't get a lot of reactance from ferrite cores at HF. You
can get a considerable amount of impedance, but for the ferrite types
which provide it, the impedance is largely resistive, not reactive. The
most common material, Fair-Rite type 43 and equivalents, has a Q of 1 (R
= X) at a frequency of a few MHz, and is increasingly resistive above
that. But even with the highest impedance materials, you'll likely need
quite a few cores with substantial cross section at each location.
Anyone interested in ferrite impedance properties can visit the
Fair-Rite web site to learn more.

A choke at a high-impedance point doesn't do much, since there's no
substantial current at that location to block. You should put the choke
about a quarter wavelength from there where the current is nominally
high. The presence of the choke can move the locations of high and low
voltage and current points, so you'll need a choke at least about every
quarter wavelength to make sure there's no point where substantial
current can occur.

Others have pointed out that ferrite chokes might be a viable way of
effecting RF isolation on conductors carrying low frequency AC, such as
power lines. But I maintain that it's not a good solution for guy wires,
which was the subject of the original posting.

Roy Lewallen, W7EL

Antonio Vernucci wrote:
It would require multiple beads at each point, and at multiple points.
While it could be made to work, it would be heavy and expensive.
That's why egg insulators or non-conductive guys are used instead.

While in a balun a reactance of say 1000 ohm would be more than adequate
for the purpose of avoiding radiation (or reception) by common-mode
currents, in the proposed application (guy-wires) a much higher
reactance would be required. As a matter of fact at the top of the
tower, where there is a voltage peak, the impedance is very high, and
the guy-wire insulator (either an egg or ferrite beads) should then show
a very high reactance value (probably in the region of tens of thousands
of ohm) not to disturb the antenna.

I never played with ferrite beads, but I have a rather strong feeling
that such high reactance values are hard to obtain at 3.5 MHz just using
beads.

73

Tony I0JX

Isolation of guy wires
 

Roy Lewallen wrote in
:

....
A choke at a high-impedance point doesn't do much, since there's no
substantial current at that location to block. You should put the
choke about a quarter wavelength from there where the current is
nominally high. The presence of the choke can move the locations of
high and low voltage and current points, so you'll need a choke at
least about every quarter wavelength to make sure there's no point
where substantial current can occur.

Roy, NEC models suggest that lossy chokes (eg suppression sleeves or cores
where Q is very small) don't modify the current distribution much unless
they are of sufficiently large impedance, and that introduction of low Z
chokes just introduces another loss without much impact on the current
distribution or resultant antenna pattern.

The magnitude of Z needed to be effective in forcing a current minimum at a
point might be quite impractical to implement using suppression sleeves, so
the time honoured insulator looks the better solution.

Owen

Isolation of guy wires
 

Owen Duffy wrote:

Roy, NEC models suggest that lossy chokes (eg suppression sleeves or cores
where Q is very small) don't modify the current distribution much unless
they are of sufficiently large impedance, and that introduction of low Z
chokes just introduces another loss without much impact on the current
distribution or resultant antenna pattern.

The magnitude of Z needed to be effective in forcing a current minimum at a
point might be quite impractical to implement using suppression sleeves, so
the time honoured insulator looks the better solution.

Yes, that's exactly the point I've been trying, apparently
unsuccessfully, to make. It is practical to use ferrite sleeves for
suppression of current at a single point or a couple of points, as Walt
Maxwell pointed out some time ago. Often called the "W2DU balun", it's
done by putting a lot of cores -- typical several tens of cores -- over
the line. But you wouldn't want to do this at a dozen or two points on
guy wires. I personally prefer to use multiple turns on a single core,
because ten turns on one core gives the same impedance a single pass
through 100 cores. But then I don't run so much power that I need to use
RG-8 or larger size cable or go to heroic efforts to insulate the turns
on a single core.

The guy wire requirements would be about the same as for a "current
balun" (common mode choke) -- somewhere around 500 - 1000 ohms is
typically necessary. At that impedance level, it makes no difference
whether the impedance is reactive or resistive from the standpoint of
effectiveness in choking current or in terms of dB loss. But there can
still be enough power dissipated to overheat the cores if they're
resistive and the power level is very high. Then you're stuck with using
ferrites which are more reactive and less resistive (e.g., Fair-Rite 60
series), but they also give you a lot less impedance per core so you
need more cores yet. That makes the ferrite solution even less attractive.

Roy Lewallen, W7EL

Isolation of guy wires
 

Roy Lewallen wrote in
:

The guy wire requirements would be about the same as for a "current
balun" (common mode choke) -- somewhere around 500 - 1000 ohms is
typically necessary. At that impedance level, it makes no difference
whether the impedance is reactive or resistive from the standpoint of
effectiveness in choking current or in terms of dB loss. But there can
still be enough power dissipated to overheat the cores if they're
resistive and the power level is very high. Then you're stuck with
using ferrites which are more reactive and less resistive (e.g.,
Fair-Rite 60 series), but they also give you a lot less impedance per
core so you need more cores yet. That makes the ferrite solution even
less attractive.

Roy,

I have attempted to model the famous Carolina Windom. It takes some
guessing since it contains proprietary (ie secret) components, namely the
"balun" and the "isolator". My flat top is at 10m height.

Since they argue that the vertical feedline is an effective radiator, I
make the assumption that the balun is a "voltage" balun, and that it is
transparent to common mode current, so I have modelled the feedline as a
wire attached to (as it happens) the inner end of the short leg of the
flat top.

The "isolator" is argued to prevent the current flowing on the line above
itself from flowing on the line below itself. It is a naive notion, since
there is mutual coupling... but lets guess that it is a bunch of
supression sleeves on coax.

At 7.2MHz, the isolator is subject to appreciable current, and it does
not effectively force a current minimum until it is well over 1000+j1000.
(BTW, about half the power is dissipated in a 1000+j1000 isolator.) 2000
+j2000 is becoming reasonably effective.

I know there is a proposition that chokes such as the W2DU balun need
only have choke impedance about 10 times the nominal Zo to be effective.
I think that design constraint is effective in limiting the extent to
which such a balun unbalances the load by its own shunt impedance dropped
accross one load leg for a load~=Zo, but I think the criteria has nothing
to do with the choke's influence in forcing a current minimum in the
region of itself. It is the difference between a bench test criteria for
insertion VSWR, and what is needed when plugged into an NEC model where
the intention is to force a current minimum.

Thoughts?

Owen

Isolation of guy wires
 

Owen Duffy wrote:

...
(BTW, about half the power is dissipated in a 1000+j1000 isolator.) 2000
+j2000 is becoming reasonably effective.
...

I have a 4:1 hybrid balun (4:1 voltage balun coupled up with a 1:1
current balun). Now and then I run the full california-kilowatt to it,
I have NEVER seen the thing REAL WARM unless running into a high
standing wave, but NEVER what I would call REAL HOT.

500+ watts would shortly make it so hot it would burn fingers and smoke
even the high temp thermaleze enamel off the windings (if the balun was
forced to dissipate that power!)

I don't see where half the power could have ever been "sunk" into the
balun, no matter what freq it has been operated at, 2-30. The windings
all look in excellent shape and the core in good condition ...

Or, perhaps I misunderstood your previous post.

JS

Isolation of guy wires
 

John Smith I wrote in news:esvehb$f2v$1
@registered.motzarella.org:

Owen Duffy wrote:

...
(BTW, about half the power is dissipated in a 1000+j1000 isolator.)
2000
+j2000 is becoming reasonably effective.
...

I have a 4:1 hybrid balun (4:1 voltage balun coupled up with a 1:1
current balun). Now and then I run the full california-kilowatt to it,
I have NEVER seen the thing REAL WARM unless running into a high
standing wave, but NEVER what I would call REAL HOT.

500+ watts would shortly make it so hot it would burn fingers and smoke
even the high temp thermaleze enamel off the windings (if the balun was
forced to dissipate that power!)

I don't see where half the power could have ever been "sunk" into the
balun, no matter what freq it has been operated at, 2-30. The windings
all look in excellent shape and the core in good condition ...

Or, perhaps I misunderstood your previous post.

Perhaps.

I don't understand the term "California Kilowatt".

I don't know if you are describing the same thing I modelled, I don't
think so.

It is often overlooked that the power of an SSB telephony signal averaged
over a longish time (but not accounting for the duty cycle of "overs") is
around 15dB (a little less for speech processing), so the heating effect
of 500W PEP telephony might be more like 15W.

Owen

Isolation of guy wires
 

Owen Duffy wrote in
:

John Smith I wrote in news:esvehb$f2v$1
@registered.motzarella.org:

Owen Duffy wrote:
It is often overlooked that the power of an SSB telephony signal
averaged over a longish time (but not accounting for the duty cycle of
"overs") is around 15dB (a little less for speech processing), so the
heating effect of 500W PEP telephony might be more like 15W.

Duh, guess who left a minus sign out, should read:

It is often overlooked that the power of an SSB telephony signal
averaged over a longish time (but not accounting for the duty cycle of
"overs") is around -15dB (a little less for speech processing), so the
heating effect of 500W PEP telephony might be more like 15W.

Owen

Isolation of guy wires
 

Owen Duffy wrote:
I know there is a proposition that chokes such as the W2DU balun need
only have choke impedance about 10 times the nominal Zo to be effective.

I believe that rule of thumb applies only to matched lines,
i.e. Z0 loads. The other rule of thumb that I have heard
is 5x the antenna feedpoint impedance.
--
73, Cecil http://www.w5dxp.com

Isolation of guy wires
 

Cecil Moore wrote in
t:

Owen Duffy wrote:
I know there is a proposition that chokes such as the W2DU balun need
only have choke impedance about 10 times the nominal Zo to be
effective.

I believe that rule of thumb applies only to matched lines,
i.e. Z0 loads. The other rule of thumb that I have heard
is 5x the antenna feedpoint impedance.

Ah Rules of Thumb (ROT) abound.

The first ROT relates to what is happening inside the coax at the choke
location (or is it somewhere else), and the choke is on the outside of
the coax.

The second ROT relates to the antenna impedance, wherever that is
(perhaps it assumed feedpoint adjacent to the choke), and again relates
to the differential mode Z (or some transformation) whereas the choke
acts on common mode current.

Take for example the use of a common mode choke at the junction between
open wire line and coax in a G5RV, its behaviour seems to me to be quite
unrelated to the differential mode Z at that point, or at the dipole
centre, or anywhere else.

Owen

Isolation of guy wires
 

Owen Duffy wrote:

...
It is often overlooked that the power of an SSB telephony signal
averaged over a longish time (but not accounting for the duty cycle of
"overs") is around -15dB (a little less for speech processing), so the
heating effect of 500W PEP telephony might be more like 15W.

Owen

Hmmm, I just may pull that balun down and run a full KW into it hooked
to a dummy load to look at some temp readings over a range of bands/over
a time span ... maybe the thing has been dumping more heat than I am
aware of, time anyway to check out the system ...

JS

Isolation of guy wires
 

Owen Duffy wrote:
The second ROT relates to the antenna impedance, wherever that is
(perhaps it assumed feedpoint adjacent to the choke), and again relates
to the differential mode Z (or some transformation) whereas the choke
acts on common mode current.

The second ROT is of course for cases where the choke is
installed at the antenna feedpoint. The main function of
such a choke is to choke off *conducted* common-mode current.
The effect of the choke on inducted common-mode current is
usually unknown unless measured.

Take for example the use of a common mode choke at the junction between
open wire line and coax in a G5RV, its behaviour seems to me to be quite
unrelated to the differential mode Z at that point, or at the dipole
centre, or anywhere else.

Again, the G5RV choke is trying to prevent *conducted* common-
mode currents and only has a chance of success on certain
bands where the differential impedance is relatively low at
the junction point. The effect of the choke on inducted common-
mode current is hard to quantify without measurements.
--
73, Cecil http://www.w5dxp.com

Isolation of guy wires
 

Here are some characteristics of off-center fed dipoles which I've
observed in doing careful measurements:

1. The feepoint balun is commonly a voltage balun, which may have the
nominal claimed impedance transformation ratio over most of the HF range
when terminated with 50 + j0 ohms times the tranformation ratio.
However, the antenna doesn't have this impedance at hardly any
frequency, and can be very different at some frequencies. When presented
with load impedances typical of the antenna, the transformation ratio is
way off and becomes complex, and the balun adds considerable shunt and
series reactance.

2. Whenever a voltage balun is used to feed an asymmetrical antenna, it
creates an imbalance current in its attempt to equalize the voltages at
the two halves relative to the "cold" side of the input. This imbalance
current flows down the feedline as a common mode current.

3. Additional common mode current results from the unequal mutual
coupling between the feedline and unequal antenna halves.

4. It takes very concentrated efforts to reduce the common mode current
to a low level on all bands. Multiple current baluns (probably what the
CW calls and "isolator") are required, and even then it might also
require feedline length adjustments to get low common mode current on
all bands.

5. Without being able to quantify what the feedpoint balun will do in
terms of transformation, reactance, and common mode current generation,
it's impossible to build a model of one of these antennas with any
confidence, even if the feedline is included in the model. The best
efforts I made to measure a real antenna and its balun and build a model
based on the measurements led to generally poor agreement between the
measured and model impedance. Consequently I'm extremely skeptical of
any model that purports to predict anything about OCF dipole performance.

Roy Lewallen, W7EL

Owen Duffy wrote:
Roy Lewallen wrote in
:

The guy wire requirements would be about the same as for a "current
balun" (common mode choke) -- somewhere around 500 - 1000 ohms is
typically necessary. At that impedance level, it makes no difference
whether the impedance is reactive or resistive from the standpoint of
effectiveness in choking current or in terms of dB loss. But there can
still be enough power dissipated to overheat the cores if they're
resistive and the power level is very high. Then you're stuck with
using ferrites which are more reactive and less resistive (e.g.,
Fair-Rite 60 series), but they also give you a lot less impedance per
core so you need more cores yet. That makes the ferrite solution even
less attractive.

Roy,

I have attempted to model the famous Carolina Windom. It takes some
guessing since it contains proprietary (ie secret) components, namely the
"balun" and the "isolator". My flat top is at 10m height.

Since they argue that the vertical feedline is an effective radiator, I
make the assumption that the balun is a "voltage" balun, and that it is
transparent to common mode current, so I have modelled the feedline as a
wire attached to (as it happens) the inner end of the short leg of the
flat top.

The "isolator" is argued to prevent the current flowing on the line above
itself from flowing on the line below itself. It is a naive notion, since
there is mutual coupling... but lets guess that it is a bunch of
supression sleeves on coax.

At 7.2MHz, the isolator is subject to appreciable current, and it does
not effectively force a current minimum until it is well over 1000+j1000.
(BTW, about half the power is dissipated in a 1000+j1000 isolator.) 2000
+j2000 is becoming reasonably effective.

I know there is a proposition that chokes such as the W2DU balun need
only have choke impedance about 10 times the nominal Zo to be effective.
I think that design constraint is effective in limiting the extent to
which such a balun unbalances the load by its own shunt impedance dropped
accross one load leg for a load~=Zo, but I think the criteria has nothing
to do with the choke's influence in forcing a current minimum in the
region of itself. It is the difference between a bench test criteria for
insertion VSWR, and what is needed when plugged into an NEC model where
the intention is to force a current minimum.

Thoughts?

Owen

Isolation of guy wires
 

"Walter Maxwell" wrote in message
...
On Fri, 09 Mar 2007 12:56:12 -0800, Roy Lewallen wrote:

Ralph Mowery wrote:
Has anyone thought of trying to use some of the ferrite beads to isolate
the
guy wires of a tower for RF so the tower could be shunt fed ? Along the
same
lines could the beads be used to electrically brake up the wires into
non
resonate lengths ?

It would require multiple beads at each point, and at multiple points.
While it could be made to work, it would be heavy and expensive. That's
why egg insulators or non-conductive guys are used instead.

Roy Lewallen, W7EL

Yes Ralph, beads could be used to achieve what you want. I refer you to a
paper
that will appear in Reflections 3 as Chapter 21A, which is a continuation
of
Chapter 21 in Reflections 1 and 2. Chapter 21 tells of the need for a
balun, and
how the beads perform as a balun.

However, Chapter 21A describes how I developed the idea for using beads
for the
W2DU balun. The idea came as a spin-off from a method I used during
radiation-pattern measurements for the antennas that flew on TIROS weather
satellites. The downlead for the signal received from the antennas on the
satellite was reradiating EM energy, and distorting the radiation
patterns. I
reasoned that placing a bead every quarterwavelength along the downlead
would
breakup the current on the lead, which it did. I then transformed the idea
into
the W2DU balun, which is described in all editions of the ARRL Handbook
since
around 1985. Chapter 21 is a repeat of my article in QST for March 1983.

Chapters 21 and 21A can be found for downloading on my web page at
www.w2du.com.
Click separately on 'View Chapters from Reflections 2' for Chapter 21, and
click
on 'Preview Chapters from Reflections 3' for Chapter 21A.

Hope this helps.

Walt, W2DU

Walt I have seen some of your work in the handbooks and it makes for good
reading. I do use a current balun on a triband beam I have up.

I just have not seen any beads used on guy wires and did not know if it had
been tried. I agree it probably would be beter to just use the insulators
on the guy wires, but not sure how the price of them and the clamps would
compair to the beads. With the guy wires already in place it may just be
easier to place some clamp on beads on the guy wires if it would work.

73 de KU4PT

Isolation of guy wires
 

On Sat, 10 Mar 2007 14:38:00 -0800, Roy Lewallen wrote:

Owen Duffy wrote:

Roy, NEC models suggest that lossy chokes (eg suppression sleeves or cores
where Q is very small) don't modify the current distribution much unless
they are of sufficiently large impedance, and that introduction of low Z
chokes just introduces another loss without much impact on the current
distribution or resultant antenna pattern.

The magnitude of Z needed to be effective in forcing a current minimum at a
point might be quite impractical to implement using suppression sleeves, so
the time honoured insulator looks the better solution.

Yes, that's exactly the point I've been trying, apparently
unsuccessfully, to make. It is practical to use ferrite sleeves for
suppression of current at a single point or a couple of points, as Walt
Maxwell pointed out some time ago. Often called the "W2DU balun", it's
done by putting a lot of cores -- typical several tens of cores -- over
the line. But you wouldn't want to do this at a dozen or two points on
guy wires. I personally prefer to use multiple turns on a single core,
because ten turns on one core gives the same impedance a single pass
through 100 cores. But then I don't run so much power that I need to use
RG-8 or larger size cable or go to heroic efforts to insulate the turns
on a single core.

The guy wire requirements would be about the same as for a "current
balun" (common mode choke) -- somewhere around 500 - 1000 ohms is
typically necessary. At that impedance level, it makes no difference
whether the impedance is reactive or resistive from the standpoint of
effectiveness in choking current or in terms of dB loss. But there can
still be enough power dissipated to overheat the cores if they're
resistive and the power level is very high. Then you're stuck with using
ferrites which are more reactive and less resistive (e.g., Fair-Rite 60
series), but they also give you a lot less impedance per core so you
need more cores yet. That makes the ferrite solution even less attractive.

Roy Lewallen, W7EL

Apparently no one on this thread has read my Chapter 21A from my web page at
www.w2du.com, where I showed that placing one #43 bead at every 1/4 wl along a
feed line eliminated the current flowing on it while immersed in an EM field in
the 130 to 150 MHz frequency range. It was the success of this one bead approach
during radiation-pattern measurements of spacecraft antennas that led to the
development of the W2DU balun with several beads at one location.

Walt, W2DU

Isolation of guy wires
 

On Sun, 11 Mar 2007 03:48:28 GMT, Walter Maxwell
wrote:

Apparently no one on this thread has read my Chapter 21A from my web page at
www.w2du.com, where I showed that placing one #43 bead at every 1/4 wl along a
feed line eliminated the current flowing on it while immersed in an EM field in
the 130 to 150 MHz frequency range.

Hi Walt,

A prophet is not recognized in his own country. If Art could write as
clearly as you (and to some practical purpose) perhaps his cries would
have merit.

However, as to the content of your Chapter 21A. It seems to me I had
come across this treatment some time ago. It inspired me to use your
W2DU balun specification, and spread the beads along a 20 feet length
of cable for exactly the reasons that initially motivated your first
use of them. If every quarterwave can be snubbed by one bead, then
certainly every 40th of a wave can be snubbed even more by the same
resistance. As I saw it, it was the same investment in beads, and the
same bulk resistance even if Kirchoff would point out that their
spread injected significant wavelength into this to invalidate his
lumped circuit analysis of total resistance. Be that as it may,
conceptually, the shorter element's smaller radiation resistance in
relation to the single bead sees a significantly higher port isolation
through the bead.

As for the practicality of a retro-fit, now that's another question.

73's
Richard Clark, KB7QHC

Isolation of guy wires
 

On Sat, 10 Mar 2007 22:51:48 -0800, Richard Clark
wrote:

the shorter element's smaller radiation resistance in
relation to the single bead sees a significantly higher port isolation
through the bead.

As Reggie might have observed, the distributed resistance would
conform to the analogy of distributed inductance and capacitance whose
total contribution would be an extremely lossy transmission line.

73's
Richard Clark, KB7QHC

Isolation of guy wires
 

On Sat, 10 Mar 2007 23:45:35 -0800, Richard Clark wrote:

On Sat, 10 Mar 2007 22:51:48 -0800, Richard Clark
wrote:

the shorter element's smaller radiation resistance in
relation to the single bead sees a significantly higher port isolation
through the bead.

As Reggie might have observed, the distributed resistance would
conform to the analogy of distributed inductance and capacitance whose
total contribution would be an extremely lossy transmission line.

73's
Richard Clark, KB7QHC


Exactly!

Walt, W2DU