Thread | Brutkey

This distinctive stacked dual antenna arrangement is used to lower the radiation angle of the antenna, concentrating transmitted power to the "ground wave" and reducing energy that would otherwise be sent upward into the sky.

The smaller (300 foot) freestanding mast in the background left is not in current use. It can be used as an emergency spare antenna for KNBR during maintenance of the taller main antenna.

Matt Blaze
@mattblaze@federate.social

The antenna field is in the final approach and takeoff flightpath for SFO airport's runways 28L/R (and 10L/R), and so the site has special markings to warn pilots of a collision hazard. In addition to the usual tower lights and red/white paint, 3-dimensional "HAZ" warnings were installed around the field. These are easily visible in areal photos; see, e.g., https://earth.google.com/web/@37.5471204,-122.23429544,0.73120256a,577.14725587d,35y,0.01179999h,0t,0r/data=CgRCAggBQgIIAEoNCP___________wEQAA

Matt Blaze
@mattblaze@federate.social

Note, important safety tip: you can get closer to this tower without clearly trespassing or jumping fences than most other 50KW broadcast antennas I've encountered. I measured a field strength of over 80V/m a bit outside the tower fence, which is an incredibly strong signal (though still within OSHA limits at the frequency involved).

Resist any temptation to jump the fence and climb the (energized) tower. You'd be electrocuted as soon as you touched it.

jwz
@jwz@mastodon.social

@mattblaze@federate.social Not that I have any interest in testing it, but I'm curious about the "electrocuted as soon as you touch it" part. I assume that means the tower dumps a bunch of juice between you and ground, but if it was that easy, wouldn't there be a constant lightshow of arcs around its base as twigs, leaves, pigeons and squirrels got vaporized?