Pontiac CO, MI

Thanks to Ken Hoehn and Eric Walli for contributing this information.

Pontiac CO [Central Office], or Pontiac Main, is located at 35 Mill Street, near Huron Street (Rt. 59). The building was constructed in 1928, as indicated by the date carved into its granite wall. Pontiac had both Michigan Bell Telephone (MBT) and AT&T microwave radio equipment, with antennas on a partially-enclosed rooftop tower.

A January 1970 AT&T Long Lines route map shows Pontiac CO having a single microwave route going west-southwest to Milford. The destination of the second set of antennas seen in the photos below has not been determined.

Pontiac was home to the Pontiac IMTS (Improved Mobile Telephone System) facility. The building housed both UHF (in the 454 MHz range) and VHF (152 MHz) automatic mobile facilities.

Originally, Pontiac also hosted the 158.100 MHz 'Bellboy' paging system, but that had to be moved, for one of the VHF mobile channels receive (mobile to base) frequencies was only 20 or so KHz removed and the Bellboy transmitter was desensing the mobile receiver. The Bellboy transmitter was moved about 5 blocks west to another building.

In addition, Pontiac housed a 451.350 MHz repeater for AT&T's Telephone Maintenance Radio System.

When the President visited the area, federal government technicians installed temporary radio communications equipment at Pontiac.

The box-like tower atop the building is in fact a steel tower covered to match the building's exterior. The covering is solid about halfway up the structure, while the upper half is provided with rectangular window-like openings at various levels for the microwave antennas. To ascend the tower, one would climb up a ladder in the warm interior of the 'box', and stop at a Barco door-type hatch. Then the climber would open the hatch, and crawl out on the 'roof', which is just below the lowest 'window' seen in the accompanying pictures.

Unfortunately, the tower's 'windows' and its interior steelwork made the structure a perfect home for the many pigeons which infest downtown Pontiac. A radio engineer who worked on the antennas describes almost losing a shoe as his foot sank into the 12-18 inch thick layer of pigeon droppings, weighing literally tons, which covered the roof.

In three of the photos, note that the tower's red obstruction light is on. Pontiac, like most MBT radio towers, ran the light 24 hours. When it flashed, it did not go off; that would stress the lamp filaments too much. The flasher switched in and switched out a high-current resistor in series with the lamp that kept the lamp 'warm' during the off cycles. The actual sequence was not ON-off..., but rather BRIGHT, very dim, BRIGHT, very dim...


Photos courtesy of Eric Walli
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Updated on February 10, 2003 at 12:30 by Albert LaFrance