Hi Jim.... I am working my way through your piece, and getting the
drift that clamp-on ferrite beads do not typically hurt me, but unless
I have A LOT of them, they won't help much (if at all).
I did like this quote (taken slightly out of context, of course...) :
Receiving Antennas benefit significantly from the addition
of a common mode choke to isolate the antenna from its
feed line. Both ends of the RG6 feed line to each of my
Beverages takes 8 turns through one of the Big Clamp-Ons.
And yet, if I read your Figure 35 on page 26 correctly (unlikely, but
I will try, anyway...) it seems to say one needs A LOT of ferrite beads
to make a substantial difference - on, say 40-10 meters, even more on
lower bands - but the chart indicates numbers tested were like 20 and 40
beads... and if those are the typical 1/2 inch long beads (or the .19"
beads mentioned int he text), then it seems one needs just 20-25 inches
of beads to have some meaningful
impact / effect. THAT seems tolerable if one was going to use clamp-on
beads - as did W0IYH using a string of clamp-on beads on his 10M
antennas - with good effect (acknowledging he preferred them over other
types for convenience and specific reasons associated to a phased
cabling already in place...)
So, they seem to have some positive effect - BUT AM I CORRECT THAT THEY
HAVE NO SIGNIFICANT DELETERIOUS OR HARMFUL EFFECTS if placed on the coax
near the feed point?
I am especially interested in whether or not they might have more or
better impact on a receiving antenna than on one I transmit with. I
use several receive only antennas, and anything to lower noise thereon
is a bonus. I would anticipate they would be more benign in a receive
only setting than on a transmit - receive setting.
Any traction? Or just wasting my time.
============================= JHR =============================
On 8/8/2010 1:05 PM, Jim Brown K9YC wrote:
benefit from reading my tutorial on coaxial chokes. Dissipation can be
made quite small if you make R large enough, and, as it turns out, it's
easy (and inexpensive) to do that if you understand the materials.
http://audiosystemsgroup.com/RFI-Ham.pdf
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