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 ?

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

"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

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

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

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

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

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

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

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