• Matt Blaze@federate.socialOP
    2·
    6 days ago

    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.

    • Matt Blaze@federate.socialOP
      2·
      6 days ago

      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.

      • Matt Blaze@federate.socialOP
        2·
        6 days ago

        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.

        • Matt Blaze@federate.socialOP
          2·
          6 days ago

          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.

        • vxo@digipres.club
          1·
          6 days ago

          @[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.