About a dozen of the students in my surveillance course surprised me by attending the hearing. Big thanks to the committee staff who went out of their way to accommodate everyone.

For those who don't follow legislative minutiae, there was a hearing on Salt Typhoon (and, inevitably, Signal) yesterday in House Government Reform.

My testimony focused on how Salt Typhoon was enabled by telecom wiretap mandates dating back to the Communications Assistance for Law Enforcement Act of 1994.

Video of the hearing and written testimony are online here: https://oversight.house.gov/hearing/salt-typhoon-securing-americas-telecommunications-from-state-sponsored-cyber-attacks/

The biggest security breach in that Signal transcript wasn't anything that was said, or even that a journalist was added to it. It was the complete absence of anyone saying "hey, should we really be discussing this over Signal?"

Obsolete secret infrastructure like CARTWHEEL tower, only revealed decades later, intrigues me not just for its scale and design, but also for the obvious question it gives rise to. If this stuff effectively managed to stay unnoticed for decades, what newer secrets are hiding under our noses today?

Despite CARTWHEEL being located in the middle of a residential neighborhood in a busy city and staffed by military personnel, officials went to great lengths to conceal the true purpose of these towers. They hid in plain sight, appearing to be silos or water towers (they even used civilian water trucks to send crews to some of the towers).

It was only after the cold war ended that the details of the network were declassified.

The upper white section of the tower is actually a plexiglass radome, concealing various microwave and UHF radio antennas.

CARTWHEEL and its cousins were decommissioned around 1990. Most of the towers, mainly atop mountains in remote areas, were demolished or left to rot. However, CARTWHEEL and CORKSCREW (on a mountain near the Appalachian trail in central Maryland) have been maintained in good condition, now repurposed by the FAA.

Captured with the Rodenstock 23mm/5.6 HR Digaron-S lens (@ f/6,3), Phase One IQ4-150 back (@ ISO 50), Phase One XT camera (1/25 sec exposure).

This unassuming cylindrical tower, at first glance perhaps a grain silo or water tower, was part of a secret "continuity of government" microwave communications network. Built in the early 1960's, a network of similar towers located around the capital region linked the White House with critical sites such as Camp David, Raven Rock, and Mount Weather.

"CARTWHEEL" Tower, Fort Reno, Washington, DC, 2020.

All the pixels, none of the continuity of government, at https://www.flickr.com/photos/mattblaze/49576247768

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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.

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

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 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.

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.

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.

Rodenstock 50mm/4.0 HR Digaron-W lens (@ f/6.3), Phase One IQ4-150 digital back, Cambo 1250 camera (vertically shifted -23mm).

This simple photo pushed the 50mm lens to the limits of its image circle with the large shift required to keep the tall antenna mast fully in the frame while maintaining its geometry. Hard vignetting of the upper corners was visible in the full sensor image, but fortunately the composition benefited from a narrower aspect ratio that cropped out the dark corners.

KNBR (AM 680) Antennas, Redwood City, CA, 2024

All the pixels, none of the vertigo, at https://www.flickr.com/photos/mattblaze/54131419266

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In 1960, the station was sold to the "Far East Broadcasting Company", which changed the format to chiefly Christian religious programming. The station ceased operation in 1994, and its antenna field was razed soon afterward.

Fortunately, the transmitter house survives and remains in excellent condition. It currently belongs to a wastewater treatment plant located adjacent to the site. I believe the building is now leased out as office space.

KGEI was a 250KW commercial shortwave international radio broadcast station. Originally constructed, owned and operated by General Electric, the station opened in 1939 on San Francisco's Treasure Island. In 1941, it moved to a permanent site in Redwood City. This building housed the transmitter and control facilities; the exterior walls are three feet thick, to better resist any WW II enemy bombings. At the time, KGEI was the only US broadcast station capable of reaching across the Pacific.

Captured with the Rodenstock 50mm/4.0 HR Digaron-W lens (@ f/6.3), Phase One IQ4-150 digital back, Cambo 1250 camera (vertically shifted -5mm).

This modest but handsome, art-deco-accented building was built in 1941 to house the transmitter for "KGEI", a commercial shortwave radio broadcast station whose programming could be heard across the Pacific. It shut down for good in 1994.

KGEI Transmitter Building, Redwood City, CA, 2024.

All the pixels, none of the RF radiation, at https://www.flickr.com/photos/mattblaze/54131707918

#photography