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facilities:microwave:oak_hill [2026-05-10 16:49] – J. B. Crawfordfacilities:microwave:oak_hill [2026-05-10 21:22] (current) – J. B. Crawford
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 ====== Oak Hill Microwave Station ====== ====== Oak Hill Microwave Station ======
  
-Oak Hill is a distinctive microwave site located on Communications Hill in San Jose, California. Many will recognize Oak Hill for the unusual concrete tower, which sits above an underground building that is semi-hardened at most. Much about the history of Oak Hill is obscure, including the reason for the unusual construction. Functionally, Oak Hill was a microwave station and likely also exchanged microwave traffic with an L-carrier cable that runs north-south through California.+Oak Hill is a distinctive microwave site located on Communications Hill in San Jose, California. Many will recognize Oak Hill for the unusual concrete tower, which sits above an underground building that is semi-hardened at most. Much about the history of Oak Hill is obscure, including the reason for the unusual construction. Functionally, Oak Hill was a microwave station for connectivity to the San Jose CO and likely also exchanged microwave traffic with an L-carrier cable that runs north-south through California.
  
-^ Built    | Late 1960s? |+^ Built    | 1972 |
 ^ Builder    | AT&T | ^ Builder    | AT&T |
 /* Suggested table rows: */ /* Suggested table rows: */
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 | Hogsback | Southeast | Microwave | | Hogsback | Southeast | Microwave |
 | Sunnyside | Northwest | Microwave | | Sunnyside | Northwest | Microwave |
 +| East Bay Hills | ??? | Microwave |
 +| Redwood City | ??? | Microwave |
 | Gilroy | South | L-carrier | | Gilroy | South | L-carrier |
 | Dunnigan | North | L-carrier | | Dunnigan | North | L-carrier |
 | San Jose | North | WLEL | | San Jose | North | WLEL |
 +
 +This list is probably incomplete and confusing, the routes seem to have changed over time. A [[https://groups.io/g/coldwarcomms/message/4739|mailing list post]] from Wayne M H also gives the following. I am not familiar with the maps referenced.
 +
 +  The map I have that seems post-1979 shows Oak Hill with a MW path to
 +  Starr Canyon (aka "Hogsback" and was moved from the San Jose office in
 +  1975), Walpert Ridge, Redwood City (1974 along the path), Loma Prieta
 +  (1975 along the path), and possibly others to the San Jose office.
 +  
 +  Another map, or diagram rather, with "AT&T Communications" at the
 +  bottom has Oak Hill with a Lenkurt path to Sunnyvale (Now a PacBell
 +  switch), a DR11 / 609E(?) path to Redwood City (Current AT&T Office),
 +  lightguide to San Jose 02, WLEL(?) to San Jose 02, and TD2 / 609E to
 +  Loma Prieta, and the 11GHz Lenkurt dual path to Starr (For Pacheco
 +  Pass).
  
 ==== History ==== ==== History ====
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 The history of the Oak Hill site is not well documented, but LinearBob WA6WHT sent [[https://groups.io/g/coldwarcomms/message/23744?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Arecentpostdate%2Fsticky%2C%2Coak+hill%2C20%2C2%2C20%2C53551270|an explanation]] to the ColdWarComms list that goes like this: AT&T originally intended to add floors to its downtown San Jose office (on Almaden Road) and mount microwave antennas there, but expansion of the San Jose Airport lead the FAA to prohibit the added height. Instead, AT&T selected the Communications Hill site, which was already known by that name due to a Santa Clara County emergency communications facility nearby. This became known as "Oak Hill" within AT&T, and the microwave facility served mostly as a "remote" radio site for the San Jose downtown office. The history of the Oak Hill site is not well documented, but LinearBob WA6WHT sent [[https://groups.io/g/coldwarcomms/message/23744?p=%2C%2C%2C20%2C0%2C0%2C0%3A%3Arecentpostdate%2Fsticky%2C%2Coak+hill%2C20%2C2%2C20%2C53551270|an explanation]] to the ColdWarComms list that goes like this: AT&T originally intended to add floors to its downtown San Jose office (on Almaden Road) and mount microwave antennas there, but expansion of the San Jose Airport lead the FAA to prohibit the added height. Instead, AT&T selected the Communications Hill site, which was already known by that name due to a Santa Clara County emergency communications facility nearby. This became known as "Oak Hill" within AT&T, and the microwave facility served mostly as a "remote" radio site for the San Jose downtown office.
  
-Based on LinearBob's story, construction of Oak Hill would have been sometime in the late 1960s or 1970s. Indeed, historic aerial images bracket it between 1968 and 1980.+Based on LinearBob's story, construction of Oak Hill would have been sometime in the late 1960s or 1970s. Indeed, historic aerial images bracket it between 1968 and 1980, and a tangential mention in a San Jose planning document puts the date of construction at 1972.
  
 Microwave IF signals were conveyed between San Jose and Oak Hill over 4-5 miles of coaxial cable, allowing most of the mux equipment to stay at San Jose and perhaps explaining the relatively small floor area and power plant at Oak Hill. This was a system called "WLEL" or "Wireline Entrance Link," used for short-haul carriage of microwave supergroups. Microwave IF signals were conveyed between San Jose and Oak Hill over 4-5 miles of coaxial cable, allowing most of the mux equipment to stay at San Jose and perhaps explaining the relatively small floor area and power plant at Oak Hill. This was a system called "WLEL" or "Wireline Entrance Link," used for short-haul carriage of microwave supergroups.
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 ===== Construction ===== ===== Construction =====
  
-The tower at Oak Hill is an unusual concrete design, unique but not unprecedented considering vaguely similar towers at some CO sites like Queene Anne Hill in Seattle. The reason for the unusual and interesting tower remains unknown. Another oddity of Oak Hill is the building, which was built by cut-and-cover or had soil piled against it later so that it is semi-underground. The roof remains exposed, but the walls are covered by sloped earth. This does not appear to be a hardening measure, especially since the building lacks blast doors or vents. Both the tower design and semi-underground building may have just been accommodations to local aesthetic objections.+The tower at Oak Hill is an unusual concrete design, unique but not unprecedented considering vaguely similar towers at some CO sites like Queene Anne Hill in Seattle. The reason for the unusual and interesting tower remains unknown. Another oddity of Oak Hill is the building, which was built by cut-and-cover or had soil piled against it later so that it is semi-underground. The roof remains exposed, but the walls are covered by sloped earth. This does not appear to be a hardening measure, especially since the building lacks blast doors or vents. 
 + 
 +Both the tower design and semi-underground building may have just been accommodations to local aesthetic objections. [[Bernal Heights]] seems to have been similarly part-buried, likely for the same reasons.
  
 When the Oak Hill site was originally built, it was isolated on the hill. The residential development around the tower is a later project. When the Oak Hill site was originally built, it was isolated on the hill. The residential development around the tower is a later project.