Kris Kirby wrote: > On Thu, 20 Sep 2007, Chris Rosing wrote: >> What other things out there "repeat" but arent repeaters? > > Digipeaters. Since no one ever made a full-duplex digipeater...
Huh? Sure they did. Our club did it in the late 80's and early 90's when regular AX.25 packet radio was a lot more popular. It was called a repeater with bit-regeneration, and they were deployed (around here anyway) inside the repeater sub-bands. The system transmitted at the same time as it was receiving. Our club had both 1200 baud VHF and 9600 baud UHF varieties on the air in our not-so-distant past. They were built to address the "hidden node" problems inherent in simplex packet radio, to have a "coverage area" where either the user was "in" or "out" of the repeater... There was minimal (but measurable) delay from input to output, just like the current D-Star, P-25, whatever... digitized voice repeaters. By having channel traffic go through a bit-regeneration repeater system, with separate input/output frequencies and good coverage, it kept stations unable to hear other stations with widly varying capabilities in RF power levels, antenna, and receiver performance, from colliding on the channel and struggling to communicate effectively on busy channels. Mathematics shows that in cases where some stations can hear others, whereas a third station (or fourth, fifth, sixth) can only hear one of the original two stations, there's a cap on effective channel throughput as eventually the channel (in the worst-case scenario) becomes saturated with re-tries to re-send "crashed" packets of data... no matter how hard you try to randomize the re-try back-off timers. In the full-duplex repeater scenario, once a particular station "captured" the repeater, they had the channel -- period -- until they stopped sending or the repeater's digital hardware forced a timeout. Nate WY0X
