Passive Microwave Repeater
Thurmont, MD

Atop Piney Mountain, about 2.7 miles north of Thurmont, is a flat, light-colored, rectangular panel, mounted in a vertical plane and facing roughly south. It is a passive microwave repeater - a metal structure which functions like a mirror to reflect a radio communications beam around an obstacle.

The only known, publicly-accessible location from which the panel can be seen is the north end of the Catoctin High School property, on MD-550 (Sabillasville Rd.), just north of its intersection with US-15 (Catoctin Mountain Hwy.) At the north end of the parking lot, adjacent to the ballfield, look north over the backstop toward the crest of the mountain. Only the front (the flat reflecting surface) of the repeater can be seen.

This passive repeater was part of a Bell Atlantic (formerly C&P Telephone) microwave link between Thurmont and Frederick, MD. The link has been decommissioned, but the repeater was not removed due to the expense involved.

The web site of Valmont/Microflect, a leading manufacturer of passive repeaters, includes a photo of passive repeaters similar to the Piney Mountain structure. Microflect's Passive Repeater Engineering handbook (PDF file, 7 MB) offers detailed information on the theoretical and practical aspects of these devices, case studies, photos and descriptions of the company's products.

Passive repeaters are the cover story in the May 1969 issue of Electronics World magazine. The article by Ray D. Thrower, titled "Radio Mirrors for Communications", is an excellent introduction to this technology. Mr. Thrower was a field service manager for Microflect.

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Updated on September 20, 2009 at 08:34 by Albert LaFrance