On 4/17/2020 9:47 AM, K6UFO Mark Aaker wrote:
Brian said: ...several other feeds that are bundled together for 40, 6, and 2
meters
in the same run up the tower...
I have always wondered if there was noise induced by "bundled" coax
cables. If you ever have a chance to check that it would be interesting.
Hi Mark,
Several thoughts.
First, each of those feedlines ought to have an effective choke at the
feedpoint.
If they're on a tower, they ought to be bonded to the tower top and
bottom for lightning protection.
Bundling essentially causes them to be a single conductor in the common
mode circuit, including the tower itself. This causes the total common
mode current to be divided between them.
The potential mechanisms I see for the coupling of noise in this
situation are 1) coax with very poor shielding, hence the mechanism
quantified by the cable's "transfer impedance" (see the RX choke pdf)
and 2) lack of proper grounding and bonding in the shack and the
building that houses it.
73, Jim K9YC
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