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history:milradio:start [2018/07/19 03:33]
Jesse B. Crawford
history:milradio:start [2019/06/18 02:57] (current)
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 ==== GWEN ==== ==== GWEN ====
-GWEN, the Ground Wave Emergency Network, or more formally AN/URC-117, was an Air Force system of nodes that switched packets in a mesh arrangement over LF bands. ​The LF range used by GWEN, at around 150kHz, could propagate over long distances via ground-wave,​ where it would receive minimal interference from EMPs in the upper atmosphere. ​ GWEN originated in late '70s with an experimental system built at Kirtland Air Force Base - this is local to me, but I have been unsuccessful in finding detailed information about this system. By the late '80s the GWEN system design was completed and it entered the deployment stage, but it reached only partial operating capability for a few years in the early '90s before being cancelled with fewer than a quarter of the planned sites constructed. +GWEN, the Ground Wave Emergency Network, or more formally AN/URC-117, was an Air Force system of nodes that switched packets in a mesh arrangement over LF bands. ​[[GWEN|Much more about GWEN]]
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-GWEN relay sites were generally unmanned, but some relay sites were co-sited with other military facilities, particularly air force bases. The primary intent of GWEN was to relay messages within SAC and between SAC and systems used by certain other relevant parties (e.g. national command authority, missile defense systems). +
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-GWEN incorporated an interesting architecture:​ GWEN sites included an HF radio which would be used for local link to the site, and then an LF radio with associated large ground-plane antenna to contact other nearby GWEN nodes. GWEN operated in digital mode using packet switching, allowing messages to be routed around inoperable or unreachable sites. I have not been able to find detailed information on the digital scheme besides that it used a fixed 2/3rd second transmit/​receive cycle, with each 644-byte packet transmitted twice using MSK at 1,200 baud... or possibly 75 baud, depending on what document you infer from. 1,200 baud seems most likely since it would allow for a 644-byte packet plus padding during the 2/3rd second cycle, assuming that each character is a byte (not completely clear). One document (a Forecast International report) suggests that GWEN used a simple "​flood"​ routing strategy where every packet was directed to every nearby node, but there is no mention of how loops are prevented. I suspect the document is simply incorrect on that point. +
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-Wikipedia gives an interesting lead: 32 GWEN sites were reused for the National Differential GPS System, so an environmental impact assessment for that system lists their locations. The NDGPS system used long-wave as well for the data broadcast, allowing reuse of the GWEN transmitter and antenna. Of course, this is only 32 of the 58 sites which were supposedly constructed. Unfortunately,​ the 1994 decommissioning may be too recent for FOIA exemptions on more complete records to have expired. I continue to occasionally dig for anything I can find about GWEN, but have not yet gotten to submitting requests under FOIA. The NDGPS report does not give exact locations for the sites but lists cities, and it confirms a GWEN site existed at Kirtland AFB after the early test system. +
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-The NDGPS system is still partially operational today, although it's scheduled to be fully decommissioned by 2020. Fortunately for my purposes, as part of the decommissioning process at least one GWEN-turned-DGPS site originally on private land has been auctioned off. From the auction documents (sale for $86,000) I was able to locate it exactly: the Medford, WI site sits at 45° 8'​41.40"​N 90°13'​49.02"​W. Google Maps history shows the site as not present at all in 1990, suggesting it was in the latter half of the first wave of construction. The most recent aerial image, dated 09/15/2013, shows the modified GWEN antenna and utility area clearly. The other site I've located by various means is Fenner, CA at 34°45'​7.00"​N 115°13'​50.26"​W. I am looking for more, but finding them in aerial imagery has proven very difficult. +
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-Throughout its short life, GWEN was hounded by public concerns around the health impacts of powerful LF transmitters. This concern appears to have been quite misguided, particularly considering the similarity of GWEN transmissions to pervasive and often higher-powered commercial AM stations, but the concern was sufficient to prompt a substantial National Research Council evaluation. This public upset has transformed,​ in the decades since GWEN's deactivation,​ into an outright conspiracy theory; casual internet searches related to GWEN turn up mostly blogs accusing modern cellular base stations of being clandestine GWEN nodes intended to harm human health or assist in some other evil deed. +
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-  * [[https://​en.wikipedia.org/​wiki/​AN/​URC-117_Ground_Wave_Emergency_Network|Wikipedia]] +
-  * [[https://​www.nap.edu/​catalog/​2046/​assessment-of-the-possible-health-effects-of-ground-wave-emergency-network|Paper on health effects]] with useful information on the system+