Collins IS-101 Radio System
Courtesy Bob Davis
This is a high power VHF over the horizon ionosphere scatter system. It is synchronous for timing reasons. It was single sideband, supressed (SSB) carrier, time division multiplex, dual diversity reception system. It featured multi teletype channels and one voice channel. When you used the voice channel the whole station knew it because the diesels hummed a song. One strange feature of the system was that it read out info faster than it was reading it in so it pause to let the system catch up. It passed a thirty day 24 hour/day reliability test before acceptance by the Air Force and it passed with flying colors. Upon completion I was re-assigned but I understand the system started having multi-path problems so modifications had to be made. To find out about that you would have to contact the Federal Electric people who received the operational contract.
At the Anchorage Alaska site, the antenna used for the IS-101 system did not conform to the specs for the rest of the line. We used the old rhombic antenna that they had been using and it seemed to work fine and perhaps that’s why we had the multipath problems that I had told you about because you would not get the directional pattern that would occur if you had a dish like the rest of the sites.