KNBR (AM 680) Antenna, Redwood City, CA, 2024
Very tall pixels at https://www.flickr.com/photos/mattblaze/54131419266
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this post was submitted on 13 Nov 2024
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Rodenstock 50mm/4.0 HR Digaron-W lens (@ f/6.3), Phase One IQ4-150 digital back, Cambo 1250 camera (vertically shifted -23mm).
The large amount of shift required to keep the tall antenna mast fully in the frame while maintaining its geometry pushed the 50mm Rodenstock lens to the very limits of its image circle, Hard vignetting of the upper corners is visible in the full sensor image, but fortunately the composition benefited from a narrower aspect ratio that cropped out the blackened corners.
KNBR is a 50KW "Class A" (formerly "clear channel") mediumwave (AM) rado station broadcasting on 680 KHz, serving the San Francisco Bay area (and, at night, most of the west coast of the US). Opened in 1922, It was originally known as KPO, (later KNBC, and still later KNBR), and soon became the flagship station for the National Broadcasting Company (NBC)'s new western radio network. It is currently owned by Cumulus Media and now broadcasts a sports format.
Mediumwave (AM) broadcast radio uses lower frequencies than other modern broadcasting and so requires much larger antennas (generally getting larger and larger as the frequency gets lower on the dial). This often entails highly customized antenna designs engineered for the particular site and station frequencies. For most radio stations (FM, TV, etc), the towers are there simply to get the relatively small antennas up high, but for AM stations like KNBR, the towers generally ARE the antennas.
@[email protected] oh that's a funky antenna! Most AM antennas aren't that intricate.
Apparently that's a "pseudo Franklin" design (I'd call it more like a collinear) with a capacity hat.
KFBK Sacramento has the only true Franklin antenna design on an AM station in the USA and it's reeeeeally funky looking. It does with two towers what some more conventional AM directionals take four to EIGHT to accomplish. It's kinda boss.
@[email protected] Yeah, KFBK is on 1530, making it at least possible to build a full Franklin antenna (2 half wave verticals stacked atop each other - a full wavelength!)
@[email protected] I wonder if the original Ampliphase development/test transmitter is still there. It's my understanding that their daily driver is a Nautel
@[email protected] Wait, which station? KNBR is (according to their license) a Gates.
@[email protected] oh I was talking about KFBK. At least as of 2009, a Nautel (not sure what model but the front panel reminds me of the V series?), a Harris DX50, and the RCA Ampliphase TX appeared to live there.
https://www.youtube.com/watch?v=97F9TO0yBNU
@[email protected] Neat!