of the remotness and vast distances between the radar stations,
tropospheric scatter (tropo) radio was used on the WACS. Tropo works
on the principle that if you use very large antennas and blast
enough RF power at the horizon, enough of the signal will be
reflected off the troposphere to provide a usable signal at the
receiver site. Communication distances of several hundred miles are
possible with enough power. Transmit powers on the system were 1, 10
The majority of the tropo links used large 60 foot square
'billboard' antennas and 10 kw amps. Other links used 28 foot foot circular
parabolics with 1 kw amps and a few used 120 foot billboard
antennas and 50 kw amps.. Each radio
path had two receive antennas to provide space diversity reception,
the idea being that if the signal faded on one antenna, it would
still be present on the other antenna, which was true most of
the time. The longer radio paths used a quad diversity system, space
and frequency diversity. All the systems were wideband FM and
operated in the 900mhz range. A more detailed explanation of troposcatter can be found
equipment at the WACS sites was all commercially available Western
Electric toll office equipment except for the tropo radio which was
manufactured by Radio Engineering Labs (REL). The original sites
used REL GS-18081 tropo and the later sites used REL AN/FRC-39
tropo. The FRC-39 was an improvement over the earlier equipment.
There was also a 1kw Collins AN/FRC-45 at Cape Lisburne that fed
Point Lay (Liz 2) on the Dewline. Cape Lisburne was also known as
The GS-18081 had a capacity of 132 voice channels or two supergoups
plus the K group. The FRC-39 had a capacity of 252 channels.
primary mux at all the stations was WECO K & L carrier, a
frequency division, AM single side band suppressed carrier multiplex.
The K carrier was a twelve channel mux operating from 12 to 60 khz. K
carrier was originally designed for open wire or cable systems but
had it's output padded down to work on the radio. The L carrier had
a maximum capability of 600 channels but was configured to the needs
of each station. The smaller end stations had as few as 24 channels while the bigger stations had
hundreds of channels. All
stations had a K group. The Cape Lisburne to Liz-2 link used a 24
channel Lenkurt 45BX mux.
The longest original link was the Cape Lisburne-Kotzebue path at 168
miles. There were two 10 kw amps on line in a quad diversity and the
receivers used parametric amplifiers in the front ends.
50kw shots were Fort Yukon to Barter Island, Adak to Shemya and Adak
to Nikolski. The Adak to Shemya and Nikolski links were the third and fourth longest tropo shots in the world, about
miles, the longest two being on the Dewline at Thule Greenland. The
Ft. Yukon-Barter Island shot was 250 miles.
The highway sites,
Delta, Tok and Glennallen were co-located with the existing Alaska
Communications Systems stations. These links used WECO TD-2 microwave, a 600 channel capacity radio operating in the 4000
mhz range and L carrier for the mux. The microwave sites did not have a K
carrier as channel capacity was not a problem. For order-wire and alarm and
control functions on the 'A' route, Clear to Canada, Motorola
VR-150 VHF radio and AN/TCC-3 carrier, a 4 channel transportable system were
used. On the
"B' route, Clear to Neklasson Lake, Lenkurt 74A microwave and WECO
ON-2 carrier were used.
The ACS was operated
by the U.S. Army Signal Corps until the early '60's when the Air Force assumed
operation. They operated these sites until about 1969 when RCA assumed
operation. The ACS equipment was primarily open wire carrier and some of the
equipment that was in service was truly antique. As an example, at Delta,
there was some WECO C carrier which was built in the '30's. It was a three
channel mux and filled an eleven foot rack.