DEWLine Communications Systems

By: Clive Beckmann

Intermediate (I) Site Communications
On the I-sites, the method of communication with the adjacent Auxillary or Main sites was via VHF Mobile Radios. I believe the original configuration was a commercial GE radio that provided 50 watts of power. Since VHF radio is line-of-sight (LOS), this power level wouldn’t always provide dependable communications. Consequently, the systems were beefed up by the addition of 250 watt power amplifiers.

This became known as the Miscom system (short for Miscellaneous Communications). This upgrade apparently provided satisfactory communications until deactivation of the I-sites.

All the GE radios and the 250 watt amps were retrieved from the Alaskan sites andstored in the Oliktok (Pow-2) hangar after deactivation where they gathered dust for several years. During the winter of ’66, they were deemed to be excess assets and were hauled about half a mile out onto the ice. At spring thaw they sank to Davey Jones’ locker, their final resting place.

TROPO Communications
Relative to the Dewline tie-in to White Alice, there was indeed a FRC-45 tropo link between Point Lay and Cape Lisburne. I believe this link was provided for at least two important reasons.

Number 1, back in the early days, the Dewline tropo system was able to provide a backup emergency voice link for top-priority circuits terminating in Europe, as a last-resort line of communications in the event trans-Atlantic cables or shortwave radio failed to provide acceptable comm. I’d never heard of the circuits being used for a real emergency, but occasionally the order would come through to set up the connections for drill.

In Alaska, manual channel patches were then accomplished at Bar Main, Pow Main, Liz-2 and Cape Lizburne. I imagine similar patches were required all along the chain going over to Europe and also going south out of Cape Lizburne over the White Alice system. Then some General in Europe would test the circuit by talking to a counterpart in the lower-48, probably in Colorado. After the test, the circuits would be restored to normal because the patches had the effect of pre-empting operational Dewline circuits.

Number 2, the Cape Liz link provided a backup surveillance data circuit for the Alaska Dewline sites.

Rearward Communications
The original Dewline rearward communications design used the IS-101 Ionoscatter Radio system. This was a data-only system that could not provide voice grade circuits. Teletype channels were routed over this system to sites at Age-X (Anchorage), Nel-X (Ft Nelson BC, Canada) and Res-X (Resolution Island NWT, Canada on the east coast). Of course, the primary function was to provide surveillance date (aircraft movements) to military authority in the lower-48.

This system used huge curtain antennae which were maintenance intensive. Because of the drawbacks of the IS-101 it was replaced in Alaska in the early ’60s by newly-installed tropo links between Barter Island and Ft. Yukon, and between Ft. Yukon and Pedro Dome outside of Fairbanks. At the time of activation of the Barter/Yukon 50 Kilowatt shot, it was one of the longest in the world at over 200 miles. Later on the Hall Beach (Fox Main, Canada) shot to P- mountain Greenland became the longest in the world at over 600 miles using 100 Kilowatt transmitters.

IS-101’s were also installed at PIN M, CAM M, and FOX M

More info on troposcatter:
The concept of troposcatter communications was believed to be viable at least as far back as the ’40s, however there was no pressing requirement demanding that funds be expended to develop the idea.

In the late ’40s, advances in long range bomber aircraft made possible the launching of a Soviet over-the-pole attack on Canadian and American targets. The defense community was really fidgety about our lack of defense against such an attack and the Dewline concept was born. This provided the perfect program to develop and utilize the troposcatter radio.

The theory was that the antenna at the transmitting site would beam the LOS signal just above the horizon where, due to earth curvature, the beam altitude would increase until it contacted the troposphere, which contained something known as the F2 layer. At this point the radio beam would become diffused and would scatter and splatter down towards the surface of the earth, well beyond the horizon from the transmitting site. If a receiving antenna was located in the pattern of the scattered beam, the signal could be captured in an FM receiver and demodulated. The big problem with this concept was that the F2 layer existed in a varying state of ionization which caused the scattered beam pattern to constantly shift about. Of course, this varied the signal level at the receiving site such that a phenomenon known as “signal fading” occurred. The result was that the receivers were constantly loosing and recapturing the signal, not a good thing for dependable communications.

For the Dewline project, Collins Radio Corp. solved the problem by implementing a technique known as “space diversity”. This was mechanized by installing not one, but two antennae (or dishes) at the receive site, each connected to a separate radio receiver. If the physical spacing of these two dishes was accurately determined by formulae relative to the signal wavelength plus other factors, the probability of both antennae simultaneously loosing the receive signal was significantly decreased. It was this breakthrough that allowed troposcatter radio to become the primary candidate for Dewline lateral communications and represented an advance in the state of the art. However, testing of the radios on a link established between Streator, Illinois, and Rockford, Illinois, revealed that a certain amount of signal fading would still occur, space diversity notwithstanding.

Additionally, later testing in the Arctic latitudes (one link between prototype sites at Barter Island (Bar Main) and Flaxman Island (Pow-3); and another between Bar Main and Bar-1) revealed that even more extreme signal fading resulted, particularly during the fall months. However, dependability of the tropo system was deemed to be good enough to go with for lateral comm where distance between sites was only about 80 miles. The fading problem precluded the possibility of use of tropo shots for rearward communications, due to the longer distances involved. For example, Bar Main to Ft. Yukon measures over 200 miles. The effects of signal fading could be reduced by increasing transmitter power, however, to support a 200 mile shot, more power was required than was technically feasible at that time. Thus, the ionoscatter system was developed for rearward communications. All the while that the dual diversity systems were being produced and installed in the Arctic, research was progressing on solving the signal fading problem.

The “space diversity” system was also known as “dual-diversity” because two signal paths existed between the transmitting site and the two antennae at the receiving site. It was suspected that doubling the signal paths from two to four would significantly reduce the fading phenomenon. However, merely increasing the number of receiving antennae failed to yield results. It was then that Radio Engineering Labs came up with a “quad diversity” system by providing a second transmitting antenna which was driven by a second radio transmitter that was tuned to a frequency separated from the frequency of the first transmitter (use of two operational frequencies was known as “frequency diversity”). Transmitting antenna #1 provided two separate paths to the two receive antennae, while transmitting antenna #2 provided two additional paths to the two receiving antennae. With four separate paths provided, the likelihood of all four radio receivers at the receiving site simultaneously loosing their signals was dramatically reduced. It was this advance that allowed long range troposcatter to be developed for the Barter Island-Ft. Yukon shot.

Additionally, advances had been made in hi-power klystron amplifiers such that 50 kilowatt and even 100 kilowatt shots were possible. The foregoing shows how closely the Dewline equipment compliment was following behind the state of the art in tropo communications. the Dewline lateral tropo shots were upgraded to quad-diversity shortly thereafter.

Clive Beckmann
Dewline, 1965-90