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If you spend any time in the mountains you will see "blank" billboards up in the hills. These are "passive repeaters"[1] for microwave networks and I am surpri

by rsync 5y ago

If you spend any time in the mountains you will see "blank" billboards up in the hills. These are "passive repeaters"[1] for microwave networks and I am surprised they weren't mentioned in the article ... [1] https://en.wikipedia.org/wiki/Passive_repeater https://en.wikipedia.org/wiki/Passive_repeater

walrus01 5y ago
Here's a 1984 vintage PDF for passive microwave repeater engineering: https://az276019.vo.msecnd.net/valmontstaging/vsna-resources/microflect-passive-repeater-catalog.pdf?sfvrsn=6 https://az276019.vo.msecnd.net/valmontstaging/vsna-resources... For the most part these are almost obsolete, the typical data link that many of them carried was one DS3, or at most, three DS3... The path loss is extreme. Usual setup was to go from a small town central office (CO), 3-5 km up to a nearby mountain, then bounce it off there, and 25-30 km to another nearby mountain. With big old power hungry PTP microwave gear that occupied a full 42U rack, took 1200W of power, and carried a whole lot of DS0. Nowadays a modern PTP microwave radio that can carry 1400Mbps full duplex in the 6 or 11 GHz bands is as little as 35W of power, so many hilltop tower sites either have built electrical grid connections, off grid solar, or whatever. Building some of those passive repeater billboards in places with no road access was very costly. Big helicopter bills and very labor intensive. You can still see a number of them on hillsides in eastern Oregon.
- jonah-archive 5y ago
  Spotted one up on Steens Mountain not so long ago: https://www.google.com/maps/@42.4584052,-118.6942825,155m/data=!3m1!1e3 https://www.google.com/maps/@42.4584052,-118.6942825,155m/da...
jcrawfordor 5y ago
Passive repeaters were certainly not common, possibly not used at all in the AT&T Long Lines network. I am not aware of any examples at least. In general AT&T did not like them, it's more common for telephone passive repeaters to have been installed by CLECs or telephone cooperatives, and later on I know MCI used some in this area. These were all later installations than most Long Lines. I'm not sure exactly why AT&T eschewed them besides the speculation that AT&T built much of their microwave network relatively early and so the attenuation may not have been acceptable given the already short range on their links. AT&T's first generation of microwave sites had to put the RF amplifier in a hut on top of the tower because the waveguide loss was unacceptable, for example. A very common place to find passive repeaters in the desert west is at dams, where they were almost invariably installed to provide the telephone connections to the power house. A later interesting example of passive reflectors is the "periscope antenna," mostly used by Western Union when they operated a microwave network for a time. The actual microwave antennas were mounted on the roof of the shack pointed up, and at the top of the tower passive reflectors at a 45 degree angle "bent" it to horizontal. It put the more maintenance intensive parts on the ground at the cost of some power loss.

by rsync 5y ago

walrus01 5y ago

Here's a 1984 vintage PDF for passive microwave repeater engineering: https://az276019.vo.msecnd.net/valmontstaging/vsna-resources/microflect-passive-repeater-catalog.pdf?sfvrsn=6 https://az276019.vo.msecnd.net/valmontstaging/vsna-resources... For the most part these are almost obsolete, the typical data link that many of them carried was one DS3, or at most, three DS3... The path loss is extreme. Usual setup was to go from a small town central office (CO), 3-5 km up to a nearby mountain, then bounce it off there, and 25-30 km to another nearby mountain. With big old power hungry PTP microwave gear that occupied a full 42U rack, took 1200W of power, and carried a whole lot of DS0. Nowadays a modern PTP microwave radio that can carry 1400Mbps full duplex in the 6 or 11 GHz bands is as little as 35W of power, so many hilltop tower sites either have built electrical grid connections, off grid solar, or whatever. Building some of those passive repeater billboards in places with no road access was very costly. Big helicopter bills and very labor intensive. You can still see a number of them on hillsides in eastern Oregon.

jonah-archive 5y ago
Spotted one up on Steens Mountain not so long ago: https://www.google.com/maps/@42.4584052,-118.6942825,155m/data=!3m1!1e3 https://www.google.com/maps/@42.4584052,-118.6942825,155m/da...

jcrawfordor 5y ago

Passive repeaters were certainly not common, possibly not used at all in the AT&T Long Lines network. I am not aware of any examples at least. In general AT&T did not like them, it's more common for telephone passive repeaters to have been installed by CLECs or telephone cooperatives, and later on I know MCI used some in this area. These were all later installations than most Long Lines. I'm not sure exactly why AT&T eschewed them besides the speculation that AT&T built much of their microwave network relatively early and so the attenuation may not have been acceptable given the already short range on their links. AT&T's first generation of microwave sites had to put the RF amplifier in a hut on top of the tower because the waveguide loss was unacceptable, for example. A very common place to find passive repeaters in the desert west is at dams, where they were almost invariably installed to provide the telephone connections to the power house. A later interesting example of passive reflectors is the "periscope antenna," mostly used by Western Union when they operated a microwave network for a time. The actual microwave antennas were mounted on the roof of the shack pointed up, and at the top of the tower passive reflectors at a 45 degree angle "bent" it to horizontal. It put the more maintenance intensive parts on the ground at the cost of some power loss.