On Saturday, September 26, 2020 at 11:14:26 PM UTC-4, Jeff Liebermann wrote:
On Sat, 26 Sep 2020 17:21:21 -0700 (PDT), Michael Terrell wrote:


What is a bypass braid? I've never heard of the term.

It was a piece of heavy braid to connect the upper mast
to the lower mast for grounding. It was supposed to prevent
lightning or static discharges from damaging the ball
bearings or their races.
Thanks. Even with the magic buzzwords, I wasn't able to find any
rotator or tower installation instructions that involved such a bypass
braid. I don't think it will do much to prevent 20,000 Amps from
turning a big antenna rotator into a metal recycling candidate. I
double if it will do much to prevent arcing from pitting the bearings.
The are a large number of bearings in the rotator and it only take a
decent connection through one bearing to discharge a static
electricity buildup. I've taken apart a few rotators and found plenty
of rust, considerable loss of grease, but no pitting (except from the
rust).

The bypass wire might also protect against an unusual situation where
a ham operator uses a tower or mast as both a monopole antenna and a
rotator mount. In transmit, the RF current will go through the
rotator bearings. That's not a problem if the rotator is not in
motion, but potentially a big problem if the bearings are moving,
arcing merrily as they roll along. To be fair, I haven't proven that
this is happening, but I'm fairly certain it could easily be tested.
The grease wasn't conductive, and would harden into an insulating
layer of varnish. That forced the downlead to carry the discharge current.