- cross-posted to:
- [email protected]
- [email protected]
- cross-posted to:
- [email protected]
- [email protected]
KNBR (AM 680) Antennas, Redwood City, CA, 2024
All the pixels, none of the vertigo, at https://www.flickr.com/photos/mattblaze/54131419266
#photography
The taller tower (550 feet) at right is the main KNBR antenna, built in 1949. It employs an unusual “pseudo-Franklin” design; it’s actually an array of two antennas stacked atop one another. The 400 foot lower section is insulated from the ground. The upper 150 foot section is insulated from the lower section. The large (50 foot) diameter “capacitance hat” at the top (reminiscent of the Parachute Jump at Coney Island) electrically lengthens the top section, saving 250 feet of additional height.
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.
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
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 touch it.
@[email protected] relevant: https://youtu.be/GgDxXDV4_hc
@[email protected] those people are insane
@[email protected] @[email protected] But in a good way, you must admit.
@[email protected] @[email protected] Absolutely!