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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