The antenna consists of a large reflector constructed of wires stretched on steel supporting structures. In addition, there are several other VHF, UHF, and CARS antennas located at the site.

Here is a photo of the site, contributed by Bryan Wade:

Photo: Bryan Wade High Resolution

At first glance, we notice several antennas in this photo:

But the VHF receiving antenna we're discussing here isn't immediately evident. Note the ten shorter towers spread across the lower half of the photo:

Note the shape of these towers:

Now imagine a series of steel wires stretched along the parabolic inner surface of these towers:

These wires define a surface in the shape of modified torus [1]. It's the same shape as the surface of a "Simulsat" satellite antenna (or, more precisely, the top half of a Simulsat):

Like the Simulsat reflector, this surface focuses incoming RF signals onto a locus of focal points (the "locus of foci"):

Sketch: Neal McLain

The immense size of this reflector provides extremely high gain at frequencies in the VHF band. Receiving antennas placed along of the locus of foci can detect these signals.

This antenna was constructed in 1965 by General Electric Cablevision. It was originally built to receive VHF television signals from two transmitter sites in the San Francisco metro area — Mt. Sutro and Mt. San Bruno — more than 100 miles westnorthwest. The following Google map identifies the locations of these four sites:



View Larger Map

Drag the map east to see Mt. Sutro and Mt. San Bruno.

Frank Baxter was Vice President of Engineering for GE Cablevision for several years. He kindly provided the following description of this antenna:



It is an antenna that is parabolic in the vertical plane and circular in the orthogonal plane. There is a locus of feed positions that exist at one half the distance of the radius of the circle. Using this characteristic permits wide angle scanning by just moving the feed point. [This] antenna was erected in about 1965 [near] Merced, California, a CATV system owned and operated by General Electric Cablevision until 1986. The screen was about 90 feet high and 360 feet long. The radius of the torus was about 100 feet. The screen was centered on San Francisco and several antennas were placed along the locus of feed positions to cover all the Bay Area signals. The support structure consisted of steel towers with the appropriate curvature and the screen was constructed using horizontal, stretched steel wire. The screen was difficult to see and soon became dubbed 'the bird catcher.' It also had a tendency to 'sing' during high winds. This antenna was the main source of Bay Area signals for a number of years, and later served as backup to the CARS microwave system that replaced it." [2]

This reflector was still standing in 1999, although the San Francisco stations were by then being imported into Cressey by a CARS-band microwave network, and the torus reflector served only as a backup. The sole remaining receiving antenna in the locus of foci was oriented toward Mt. San Bruno, site of the KTVU (Fox, Channel 2) and KQED-TV (PBS, Channel 9) transmitters.

Other antennas in the above photo are:

The UHF dish antenna on one of the short towers receives a station from Fresno, about 67 miles southeast.

Two microwave reflectors at the top of the tall tower are part of a two-hop CARS-band network used to import San Francisco stations (received off-the-air at Livermore) into Cressey and Fresno. One reflector is directed toward Livermore (60 miles westnorthwest) ; it reflects signals arriving from Livermore to a receive antenna on the roof of the equipment building at the base of the tower. The other reflector is directed toward Fresno (67 miles southeast) ; it reflects signals from a transmit antenna on the roof of the equipment building toward a receiving station in Fresno.

it reflects signals arriving from Livermore to a receive antenna on the roof of the equipment building at the base of the tower. The other reflector is directed toward Fresno (67 miles southeast) it reflects signals from a transmit antenna on the roof of the equipment building toward a receiving station in Fresno. The satellite antenna near the base of the tower is described by Bryan Wade as "the venerable old 5-meter S-A cassegrain TVRO that I put up about 1975 so folks in Merced could get HBO."

Merced and Cressey are located Merced County, which is in Fresno-Visilia DMA.

Mt. Sutro is located in the City and County of San Francisco. Mt San Bruno is located in San Mateo County. Both counties are located in the San Francisco-Oakland-San Jose DMA.