On 11/14/2010 2:20 PM, Jim Brown wrote:
On 11/14/2010 11:11 AM, Dr. Gerald N. Johnson wrote:
and they might not prevent feedline radiation and reception.
There are two causes of feedline radiation/reception -- common mode
current and conductor spacing. A common mode choke AT THE FEEDPOINT can
essentially kill the radiation due to common mode current unless the
feedline is some multiple of a half wave, in which case an additional
choke placed along the line to act as an "egg insulator" to make it less
than a half wave would kill the remaining current.
Or if the feed line isn't perpendicular to the radiator and so gets
coupled to the radiator beyond the choke.
The choke will, of course, have no effect on radiation due to spacing,
which results from the differential signal.
At HF, few common spacings are wide enough to radiate seriously. Now at
6m and 2m, 1" spacing is enough to have a lot more loss than textbook
simply from radiation.
73, Jim K9YC
73, Jerry, K0CQ
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