Topband: Share of a common mode current experience
er_araujo at yahoo.com
Sun Jun 10 11:38:41 EDT 2007
Hi Jim and all, Yes I agree with you 100% on both
I was testing with a kind of #78 material which is
more effective at that fcy (around 1.5Mhz).
I am using a home made High Pass Filter, with more
60db attenuation at that fcy but it is being bypassed
to some degree by the common mode current.
With a couple of chokes with more than 2K, the
broadcast signal is reduced by more than 30 db now
because it is being forced to pass thru the filter in
Now I am working in all cables coming down because as
soon as I connect each other cable not being treated,
the problem reappears.
I have a few questions: I understand why it is
necessary to use a low loss material like #61 at the
antenna feedpoint (QRO) where current could be high
and if so the R part of Z will need to dissipate a lot
of heat, but what confuse me a little bit with #61
1 Using a high Z mostly inductive is ok if the
combination of line length, antenna and ground
connection dont result in a capacity that combined
with that inductance may make things worse.
2 What could be ok for one band ie: Z combined in
the right direction, it could be bad in another band
where this system resonates and capture signals from
our others antennas or other sources.
3 Living at 35 mts from ground level as it is my
case, is it possible to estimate/simulate in advance
if it will be better or worse on different bands?
4 It is very difficult to get high Z with #43
material al low fcies. If I understood correctly your
measurements Jim, we will need 14 turns on 8 cores to
get aprox 2K at 1 Mhz and 4K at 2Mhz.
5 I thought to use two chokes at the antenna
feedpoint one with #61 and the other with #78 but if
due to combination of Z #61 does things worse, then
the one with #78 will need to dissipate all the heat
by the current (if any of course)
I am doing some measurements on the cores extracted
from old TV to have an idea of its characteristics,
and when done, I will append it here.
I hope this may be of interest to the community .....
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