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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.


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Matt Blaze

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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., earth.google.com/web/@37.54712


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.

by Matt Blaze ;

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NewsGoth Condensed (if you know you know)

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@mattblaze Interesting enough, another result is that the audio frequency bandwidth is a bit restricted. When Susquehanna owned KNBR, they tried to broadcast HD on it but found they couldn't because of HD's bandwidth requirements. Most listeners wouldn't notice the restricted bandwidth, since the NRSC standard limits bandwidth to ± 10 kHz and almost no modern AM receivers can go that far up anyway.


@newsgoth @mattblaze Another similar case (which might not still exist, I haven't kept track), is KOAC in Corvallis, the only shunt-fed directional array in the country.

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