There's something to that. In CATV, there was for a time a popular type
of smooth wall 75 ohm hardline called "fused disc', which had lower loss
over the 300 MHz or 500 MHz in use by cable TV at the time, but when the
bandwidth got pushed up to 1 GHz, it was found that fused disc coax had
a notch in the response. The frequency of the notch was determined by
the spacing of the discs used to keep the center conductor centered. The
location of the discs could be seen clearly by the bumps in the shield.
This cable quickly fell out of favor because of the issue.
-Steve K8LX
On 12/24/2014 9:32 PM, Hans Hammarquist via TowerTalk wrote:
Jim,
I was told (as a little child) when they installed the antenna system for
the TV transmitter in Gothenburg, Sweden at the Brudarmossen tower, a tower
I believe is around 1000' tall, they experience a mysterious, high SWR. The
reason was that the cable clamps, holding the feeder coax, were placed by
engineering precision on an equidistant that generated the added "small"
reflections that added up in phase.
Shall you believe the story? I find it very unlikely that they managed to
"hit" the spot but the story is plausible.
... and, yes, you can make a notch filter that way. To be efficient you
will need a long distance to get a deep null.
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