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