Stepping back in time inside a historic microwave relay station

Western Union microwave relay sites survey: Part VIII

Equipment building rear door, October 2004.

Entering the abandoned Jennerstown Western Union microwave relay station was like stepping back in time. Secured behind a sturdy cyclone fence and located hundreds of yards away from the nearest road on a ridge in the Allegheny highlands, the historic tower and equipment building had been bypassed being cannibalized by the telecommunications industry and had suffered little damage from looters and vandals. The Western Union relay site was a Cold War-era relic from a time when computers occupied entire rooms and when radios used vacuum tubes, not integrated circuits.

My first visit to the relay site was on a cold and windy Saturday morning in October 2004. I had met the property’s owner, Bob Mallet, at his house elsewhere on the property and wehad driven into the relay site along a utility line right-of-way. I had been surveying the Western Union Telegraph Company’s first-generation microwave relay network since early 2002 and this was my first chance to get beyond the fences and walls protecting the surviving facilities.

Gate and equipment building entrance. Tower is in the background.

In early 1945 the Federal Communications Commission granted the Western Union Telegraph Company permits to develop experimental microwave relay systems in the Mid-Atlantic region of the United States. The permits were issued shortly after a major allocation of spectrum to nongovernmental entities that received national media coverage and spurred an electronics mini-Industrial Revolution that included the widespread introduction of CB radios, car telephones, and even microwave ovens.

By January of the following year Western Union had acquired sites for nearly twenty relay stations where it had planned to build prefabricated fire lookout towers modified to accommodate the system’s revolutionary new microwave communications system.

Western Union Telegraph Company elevation and plan drawings for microwave relay sites.

Western Union’s first-generation microwave relay network required towers adapted from models used by foresters to spot fires and standardized concrete block equipment buildings. Antennas and radio equipment designed by RCA were mounted inside a metal cabin atop each of the towers. Radio equipment cabinets and each facility’s physical plant (a gas engine, banks of DC batteries, fuel supplies, and a furnace) occupied the concrete block buildings. Each site was self-sufficient, remotely controlled by one of the terminal stations and visited regularly by Western Union maintainers.

HAER architect Christopher Marston stands on the catwalk outside the tower cab. Photo by David Rotenstein, 2005.

During the October 2004 visit to Jennerstown I took lots of photos and notes to add to my growing files on the Western Union microwave network. The high integrity of this site, however, led me to approach the Historic American Engineering Record with a proposal to document the property. HAER architect Christopher Marston got a small budget and secured a HAER engineer-historian and HAER photographer for two days of intensive fieldwork in the summer of 2005.

HAER staff (Larry Lee and Jet Lowe) document the Jennerstown relay station in June 2005. Photo by David Rotenstein.

Photographer Jet Lowe shot large format black and white images of the tower, equipment building, and the surrounding landscape while engineer-historian Larry Lee assisted Marston in measuring the site. Although the measured drawings never were completed, the report I wrote and the large format photos are on file at the Library of Congress and electronic copies may be downloaded from the library’s Website. This article is adapted from my 2005 HAER report. Additional information on the Western Union microwave relay network was published in David S. Rotenstein, “Towers for Telegrams: The Western Union Telegraph Company and the Emergence of Microwave Telecommunications Infrastructure,” IA, The Journal of the Society for Industrial Archeology 32, no. 2 (2006): 5-22.

The Western Union Telegraph Company microwave relay system represents the first generation of postwar communications infrastructure that ushered in the information age or the “third industrial revolution.”[1] Licensed by the FCC and built by two communications industry pioneers – the Radio Corporation of America (RCA) and Western Union – the system laid the foundation for advances in telecommunications that began with wireless telegraphy, facsimile transmission, television, and telephony and ended with satellite communications and the Internet. The Jennerstown relay site was a node in the communications network Western Union dubbed the New York-Washington-Pittsburgh Radio Relay Triangle. The relay triangle was one of two networks Western Union built immediately after the FCC in 1945 allocated radio spectrum for microwave communications and both were among the first commercial microwave systems in the United States.

Western Union Telegraph Company microwave network map.

Jennerstown Relay

Through its Pennsylvania real estate subsidiary, the Telegraph Realty Company, Western Union acquired options on properties for microwave relay sites throughout the state. For its relay site in the Laurel Highlands of the Allegheny Mountains linking Pittsburgh with Washington, the company selected a parcel of farmland south of U.S. 30 between Laughlintown and Jennerstown, Pennsylvania. At the time the property was owned by Pittsburgh physician and educator Adolph Leo Lewin (1871-1953) who used the house he had built there as a summer residence.[2]

The Telegraph Realty Company paid Lewin $400.00 on 18 October 1945 for a 40,000-square-foot parcel plus a right-of-way for an access road and utility lines.[3] The tower and equipment building were completed in 1946 and the system went online in 1948. In 1947 Western Union liquidated and dissolved the Telegraph Realty Company in December 1947 and the subsidiary’s assets, including the Jennerstown relay site were transferred to the Western Union Telegraph Company.[4]

The Jennerstown relay site was also known as the “Laurel Hill Relay.” It was the intermediate station between the Little Savage relay in Garrett County, Maryland, 35.2 miles to the southeast and the Fort Hill relay in Pittsburgh, 49.3 miles to the northwest. Jennerstown operated on Western Union’s RB5 system and was rated for telegraphy, telephony, facsimile, and composite transmissions. Maintainer notations made on radio equipment inside the building indicate that the units were last checked in February 1963. These dates may correspond to the period that Western Union abandoned the site.

Western Union sold the property for $650.00 on 31 March 1976 to Mallet and Company.[5] Robert Mallet raises horses on the farm he uses as a weekend retreat. In July 1977 the Crown Construction Company mounted an antenna on the former Western Union tower to facilitate communications during the recovery from flooding that struck the Johnstown, Pennsylvania, region.[6]

The Jennerstown Relay is located on Pea Vine Hill, a knob on Laurel Hill in the Laurel Highlands portion of the Allegheny Mountains. Pea Vine Hill peaks at 2,900 feet above sea level and the relay station is located at this elevation. The relay site is accessed by a 0.8 mile long unsurfaced road connecting to Laurel Summit Road south of its terminus at U.S. 30. A commercial power line enters the site from the east. The relay site is situated in a clearing surrounded by mixed hardwood forest.

View of Laurel Highlands and later radio towers as seen from the cabin atop the Jennerstown relay tower. Photo by David Rotenstein, October 2004.


The relay station is enclosed within a metal chain-link fenced compound. The fence (Cyclone Fence Company) is topped by three strands of barbed wire. There are gates in the north and west sides and the compound has a gravel surface.

Jennerstown relay station compound as seen from the top of the tower. The tower reflection, equipment building, and fenced area are visible. Photo by David Rotenstein, 2005.

Equipment Building

This one-story rectangular building measures 15′ x 30′-8″ and is constructed on a concrete slab foundation. Built of concrete blocks, the building’s fenestration is functional and minimal, designed to protect the relay station’s radio equipment from the elements and from unauthorized access.

Equipment building front, gate to compound. Note warning sign on cyclone fence (right). Photo by David Rotenstein, 2005.

Equipment building rear. Photo by David Rotenstein, 2005.

There is an entrance in the building’s north façade and there is one window in its east façade. Vents with metal hoods pierce the building’s west and south facades. The front entrance has a rectangular poured concrete slab porch. The building’s main entrance has a solid-core, metal clad two-panel door that is secured by a deadbolt lock and two padlocks. The window in the east wall is a wood double-hung sash (1/1 lights) unit and it is concealed behind a pair of exterior hinged metal shutters secured on the interior by a pair of metal bars.

Equipment building exterior window. Photo by David Rotenstein, 2005.

Equipment building window. Photographed inside the radio room. Photo by David Rotenstein, 2005.

A two-panel wood door located in the south façade leads to the heater room and is secured by a single deadbolt lock. The ventilation hoods in the south and west walls are metal alloy and conceal louvered vents protected by wire mesh (0.5″) attached to the hood interior. A third louvered vent is located above the door in the south façade and this ventilates the heater room. An off center concrete block chimney with a hollow clay tile liner pierces the built-up shed roof from the heater room. There is a metal gutter that runs the length of the south wall at the roof line. At some point a gutter had been attached to the southwest corner of the building and it drained into a poured concrete spillway that empties into the tower compound interior.

A key element of the equipment building’s physical plant is an underground fuel storage tank located adjacent to the building’s south wall. Its location is marked by a concrete cone encasing the intake pipe and a metal sign mounted on the building’s south façade that reads “GAS.” The intake is sealed by a threaded metal cap

Underground gas tank intake. Photo by David Rotenstein, 2005.

marked “Fuel Oil / 204-35-SA” and “R.I. Fittings Co. / Hillsgrove, R.I.” Western Union

intended each of its relay sites to have a 120-gallon storage tank to provide for as much as six days of continuous operation. The capacity was limited to reduce the potential for “gum formation.”[7] The fuel entered the equipment building through a buried pipe and was measured by a gauge mounted inside the engine room.

Radio Room

The radio room is the first space entered once inside the equipment building. It is a rectangular open space with a single metal cabinet housing the facility’s radio equipment.

Equipment building radio room.The radio equipment is located inside the metal cabinet. The doorway in the wall on the right leads to the battery room. Visible inside are the three shelves on which back-up batteries were mounted. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

The radio cabinet is located in the eastern end and it is a vertical unit connected to the room’s south wall by two metal braces; it also is connected to a power source and tower relay equipment via metal conduits attached to the cabinet’s top. These conduits are suspended from the ceiling by metal straps. There is a metal heating duct that follows the southern ceiling/wall.

Radio equipment inside radio room cabinet. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

Radio room thermostats. Photo by David Rotenstein, 2005.

Electrical fixtures in the equipment room include a single electric bulb socket in the ceiling, electrical outlets attached to the north and south walls, and a light switch (to control lighting in the radio room, battery room, and heater room) on the north wall. There is a pair of thermostat controls for the heating system on the south wall, both manufactured by the Minneapolis-Honeywell Regulator Company. The eastern (left) side thermostat controlled the radio room – it is labeled in pencil, “Room Temp Control” – and the west (right) unit is marked in pencil “Frigistat” on its cover (this unit also is marked “40°” and “Reads 2° Low”).

The radio equipment is housed in a vertical rectangular metal double-cabinet approximately 7′-1″ high with two 1′- 7 3/16″-high racks. The cabinet originally was designed as a four-door unit (two in front, two in back), but only the pair of rear doors remains. Each rack was designed to mount transmission, reception, and power supply units associated with west-east or east-west traffic. The panel controls (meters, switches, etc.) and tubes are broken, heavily oxidized, or removed on some of the units; others, like the MI-31521 amplifier in the west-east rack (left) are intact with minor damage. The 7446-A amplifier unit is notable in the left rack because it has maintainer notations in black magic marker on its face. The notes read “Tubes checked 2/13/63,” suggesting the unit’s last inspection while in service was in the winter of 1963.

Radio equipment showing marks made by the last maintainers to check the relay station in 1963. Photo by David Rotenstein, 2005.

Battery Room

Located in the southern portion of the building, the battery room is entered from the radio room through a solid metal door. The rectangular room has three wood shelves (paired beams) mounted on the southern wall by metal bars anchored in the concrete block. The shelves held a bank of fifty-seven batteries connected to the station’s vibrator unit (power supply, e.g., an inverter to transform direct current into alternating current, located in the engine room).[8] There are 45-amp fuses attached to each shelf; these in turn are connected by wire conduits to a stamped steel switch box mounted on the battery room’s west wall. The 60a/250V single throw switch box was manufactured by the Square D Electrical Company (Catalog number 84252, Series no. 3).

Battery room. Note remaining battery on floor. Photo by David Rotenstein, 2005.

Engine Room

Engine room showing concrete engine mount on the floor, switch box, and louvered vent. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

This rectangular room is located in the western portion of the building and it is entered from the radio room through a solid metal door. A raised rectangular concrete foundation (5′-0″ x 2′-0″) for a four-cylinder gasoline engine occupies the center of the floor. The fuel pipe that enters from the foundation on the west side of the concrete platform is sheared off. Machinery in the room includes electricity regulating equipment and motors to operate louvers in vents that pierce the south and east walls. The vent in the west wall was intended to carry air heated by the engine’s radiator out of the building. When in operation, the engine was connected to this vent by a canvas duct.[9] The vent in the south wall allowed fresh air to enter the room. Both vents had electric motors attached to linkages that opened the louvers while the engine was running. Engine exhaust exited through a pipe in the building’s south wall.

Engine room. Concrete mounting block detail. A starter battery was attached to the motor and it was mounted on the horizontal metal frame. Photo by David Rotenstein, 2004.

Louvered vent in engine room. Note the electric motor and chain used to automatically open the vents when the engine was running. Photo by David Rotenstein, 2005.

On the west wall were mounted the fuel level gauge (“Midget Levelometer” manufactured by the Liquidomter Company of Long Island City, New York), fuse box, and master disconnect switch. The 10-circuit fuse box was manufactured by the Trumbull Electric Company of Plainville, Connecticut. The fuse box included circuits for the equipment building and tower lights.

Midget Levelometer used to read buried fuel tank levels. Photo by David Rotenstein, 2005.

Engine room. Vibrator (power supply) unit. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

The vibrator unit (inverter) cabinet still stands next to the room’s north wall. Conduits connected it and the generator to an overhead cable duct leading to the radio room. Inside the cabinet was a single-phase “constant voltage transformer” manufactured by the Sola Electric Company of Chicago, Illinois. The unit also was connected to a General Electric “voltage stabilizer” mounted on the north wall.

Western Union relay station engine room fully equipped. National Archives and Records Administration.

Heater Room

Equipment building rear showing heater room door, engine room vents, and chimney leading from the furnace. Photo by David Rotenstein, 2005.

The heater is located in a square room entered from the building’s south side. The oil-burning heater was installed in the east side of the room. It was manufactured by the Viking Manufacturing Company of Dayton, Ohio. The unit included a power supply and circulator. Exhaust was vented through a flue leading to the building’s chimney and warm air was sent into the building’s interior by way of metal ducts suspended from the ceilings. The heater was controlled by a “combination fan and limit control” box mounted on the flue. The concrete block chimney is located in the room’s southeast corner and there is a cleanout box near the room’s floor.

Heater room maintainer notes on concrete block wall. Photo by David Rotenstein, 2005. Click the image to see a larger version.

Although Western Union relay stations were unmanned, the heating units were required to prevent condensation from forming in the building’s equipment and to ensure that the inside temperature remained above forty degrees Fahrenheit to maintain battery capacity “at excessively low temperatures.”[10] Maintainer notations in pencil on the room’s west wall appear to date between 1950 and 1956 and indicate dates (e.g., 9/28/50), fuel amounts (e.g., “220 gals.”), and heater states (“on” or “off”).

Furnace inside heater room. Photo by David Rotenstein, 2005.

Tower and Cab

Jennerstown relay tower. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

The relay station’s tower, which includes its structure, cab, catwalks, stairs, certain electronic components, and conduits, is the facility’s most prominent feature. The self-supporting lattice tower is constructed of rolled, L-section members furnished by the Bethlehem Steel Company. The square-plan structure has eight panels and rises 100’, not including the cab. Each of the tower’s four legs rests on a concrete footing with beveled top edges, and each leg is secured to it by anchor bolts, washers, and dual hex nuts (the second ones are lock nuts). Each leg is electrically grounded with copper wires. Most of the horizontal and diagonal members were doubled to form the equivalents of T or cruciform sections, while a single, heavier L section sufficed for each leg.

Image courtesy U.S. Forest Service.

Using a proven Aermotor design to enable easy construction at the site, the tower’s legs, girts, and braces were bolted together using square-head bolts and hex nuts (with bolt heads generally facing out or down). Stamped metal “Palnuts,” manufactured by the Tinnerman Company, serve as locknuts. Some assemblies include washers, and gussets stiffen all major connections. All structural members, fasteners, and gussets were galvanized for corrosion resistance. This tower shows no evidence of ever having been painted orange and white for enhanced visibility from aircraft. Approximately 34,000 pounds of steel were used in the Jennerstown Tower.

Access to the cab atop the tower is through a steel interior stairway anchored by a poured concrete step. The stairway – stringers formed from pairs of L-struts connected by Warren truss webbing, open mesh treads, and L-post rails – rises seven flights to a final flight located on the tower exterior that leads to the catwalk and equipment cab at the tower’s crown. Each landing is located in alternating corners of the tower.

Tower stairs. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

The tower carries conduits for radio cables (interior) and power supply (exterior). The conduit leaves the equipment building through its south wall (southeast corner) and it is carried to the tower in a steel enclosed cable trough (also called an “ice bridge”) mounted to the tower by struts and guy wires. The conduit becomes vertical inside the tower and the power supply splits and is carried into the tower by a pipe conduit while the radio cables remain inside the square steel conduit. The steel conduit has junction boxes with access panels situated between landings.

Equipment building rear and tower base. The horizontal metal beam to the top right supported cables and other conduits leading from the building to the cabin at the top of the tower. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

Radio equipment is located in two places on the tower: in the cab and on the sixth landing. The equipment on the sixth landing consists of radio cabinets and antenna mounts located on the south and south sides of the tower. These accommodated units described in Western Union technical literature as “diversity receivers.” These receivers were added to the original engineering design to stabilize reception. The remaining equipment on the west side is an RCA MI-31400 receiver mounted inside a temperature-controlled container that contains an internal heater and external vent mounted on the unit’s exterior. The receiver’s front panel is attached to its case by hinges and its dials and controls are missing. The manufacturer’s name and model markings are visible. The heating element, a General Electric “strip heater,” was attached to the housing and its compartment retained its insulation. The radio equipment on the west side of the landing had been removed and only the heater and housing remain in place.

Radio head units on tower landing. Photo by David Rotenstein, 2005.

Western Union Telegraph Company photo of engineer inside a relay tower cab. Original in the collections of the Smithsonian National Museum of American History.

The square-plan cab at the top of the tower has a wood floor and is surrounded on all sides by a metal catwalk and metal pipe rail. It is reached by an exterior stairway leading from the seventh landing to the catwalk. The cab is accessed by a door in its north façade. The upper platform is 20′-4″ x 18′-8.5″ and the cab is 12′-0″ x 12′-0″. Mounted to the cab’s west façade is a parabolic antenna with a 3′-0″ diameter and a waveguide connecting it to the cab interior through a piercing in the west wall. The cab is clad with corrugated galvanized steel and it has a pyramidal galvanized steel roof. There is a single casement window, three-lights per frame, in the south wall and rectangular piercings in the west and south walls are covered by radio-frequency transparent fiberglass panels. The panels are perforated for ventilation; the panel in the south wall is marked with the station name. Power junction cabinets and cable conduits are attached to the interior of the north wall, east of the door.

Tower cab interior. Radio units (right), conduits, and control boxes mounted on interior walls. Note large amounts of bird droppings on the wood floor. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

Tower cab interior. Radio boxes and antenna mounts. Note RF-transparent panels behind the vertical mounts. Historic American Engineering Record photo by Jet Lowe, 2005. Library of Congress Prints and Photographs Division.

RF (radio frequency) transparent panel in cabin wall where antenna would have been located. A wave-guide pierces the panel (in the upper right) and leads to an exterior parabolic antenna. The panel is installed upside down and the writing indicates the targeted relay. Photo by David Rotenstein, 2005.

There are four bolted steel L-beams placed diagonally inside the cab at approximately 10′ above the floor. These beams served as supports for the vertical antenna and radio equipment box (head-end units) mounting racks. The antennas, which would have been mounted side by side on the racks facing the RF-transparent panels, are missing, however the mounting brackets remain connected to the racks. The head-end units cases, paired in each rack – transmitters and receivers for each direction, i.e., towards Washington and towards Pittsburgh – are intact but all of the radio equipment has been removed. Each unit was hinged to open downward and the face of each was marked with the system identified, “RB 5”, along with the appropriate label, “RECV” for receivers and “TRANS” for transmitters. The racks are consistent with RCA equipment manuals published for Western Union and are illustrated in Western Union technical and promotional literature.

Tower cab underside showing conduits entering cabin. Exterior parabolic antenna is visible in the upper right. Photo by David Rotenstein, 2005.

Tower cab interior. Roof vent, light fixture. Photo by David Rotenstein, 2005.

Wave guide part information. The wave guide is attached to the parabolic antenna mounted outside the tower cab. Photo by David Rotenstein, 2005.

Parabolic antenna mounted to the cab exterior. Photo by David Rotenstein, 2005.


[1] Louis Galambos, “Recasting the Organizational Synthesis: Structure and Process in the Twentieth and Twenty-First Centuries,” Business History Review 79 (Spring 2005): 3, note 5; Richard N. Langlois, “The Capabilities of Industrial Capitalism,” Critical Review 52, no. 4 (1992): 526.

[2] Lewin was a Prussian immigrant whose family had emigrated to the United State by way of England. He was educated in Pittsburgh and in Europe and began practicing medicine in Pittsburgh. In 1911 Lewin became a charter member of the Pittsburgh Board of Education; the property’s current owner points out that tile in some of the house’s bathrooms came from Pittsburgh schools: Robert Mallet, Personal Communication, Interview at Jennerstown Relay Site (23 October 2004); “Adolph Leo Lewin,” in The National Cyclopaedia of American Biography, Being the History of the United States, vol. XLII (Ann Arbor, Michigan: University Microfilms, 1967), 409-10;  Board of Public Education, A Study of the Educational Development of the Pittsburgh Public Schools (Pittsburgh, Pennsylvania: The Board of Public Education, 06/03/17 1928), 23.

[3] Westmoreland County Deed Book 1225, p. 588; Somerset County Deed Book 347, p. 49. Lewin’s property spanned the Westmoreland and Somerset county lines and the access road terminates in Somerset County. Instruments, therefore, were recorded in both counties.

[4] The Telegraph Realty Company transferred the Jennerstown assets on 29 December 1947. Somerset County Deed Book 375, p. 430.

[5] Westmoreland County Deed Book 2209, p. 911.

[6] Mallet, Personal Communication.

[7] H.M. Ward, “Power Supplies for Microwave Relay Systems,” Western Union Technical Review 3, no. 4 (October 1949): 136-37.

[8] Ward, “Power Supplies for Microwave Relay Systems,” 137.

[9] Ward, “Power Supplies for Microwave Relay Systems,” 136.

[10] Ward, “Power Supplies for Microwave Relay Systems,” 135.

© 2010 David S. Rotenstein

3 thoughts on “Stepping back in time inside a historic microwave relay station

  1. Was with Western Union from 1960 to 1967 as a plant tech Repairing Teleprinters,Fax, and all related equipment. Worked on the WU Microwave system from 1967-1990.
    the system was built during the cold war, so for security reasons the stations were located somewhat from civilization with terrain which required 4 wheel drive, even in good weather. Enjoyed the 30 years I spent with this Company. Mainly because of the challenge, and the fact that western Union was a Great Company to work for.

  2. I worked for WU from 1952 thru 1985. I was the first Computer Center Store Keeper at the 5 way J station at Berwick Kansas. Started as a bicycle messenger, for a time one of 3 wire chief’s at “OU” at Houston Tx. Retired as a Plant Tech at Wichita KS. WU was good to me and I enjoyed my time with it.

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