September 1935 Short Wave Craft
[Table of Contents]
Wax nostalgic about and learn from the history of early electronics. See articles
from Short Wave Craft,
published 1930 - 1936. All copyrights hereby acknowledged.
Most of us Baby Boomers remember a time when
cell towers did not present a ubiquitous (and, frankly, ugly) presence
across the landscape. Microwave relay towers for television and telephone links could be spotted sitting
atop hilltops and mountain ridges in some areas, and giant television and radio station towers sat behind
broadcast stations, and multi-element antennas dotted house rooftops everywhere. Our grandparents
great grandparents) remember when even microwave relay towers were missing. This 1936 article reports
on the first microwave links spanning the English Channel to replace expensive and trouble-prone submerged
cable. Part of the impetus, not mentioned within, was the building inevitability of war with Germany and the
vulnerability of those communications links to being compromised by Nazi submarines and divers.
Micro-Waves Span the English Channel
Fig. 1 shows the towers on top of which are mounted the transmitter and receiver
More and more uses for micro-waves are being discovered every day. This particular installation shows
how short sections of telephone or other communication transmission lines can be eliminated by micro-wave
transmitters and receivers, so long as there are no large intervening objects which might block the
transmission and reception. Because micro-waves are quasi-optical in character, the transmitters and
receivers must be mounted on high towers.
Radio engineers have at last found that the ultra-short waves or
micro-waves as they are sometimes called, can be used to take the place of telephone or telegraph circuits
to particular advantage in some cases. For instance, if we have two points between which we desire to
hold communication or transmit messages of some type and they are fairly close together (in the neighborhood
of between 10 and 30 miles) and the type of territory between these two locations does not permit the
erection of poles to carry a telephone or telegraph line and provide communication needed, micro-waves
become a very important and useful adjunct.
We can install very low-powered transmitting and receiving stations, the cost of which will be much
lower than the average radio station, because of its low power and simplicity. Secrecy can be maintained
because these waves can be focused in a very narrow beam, which excludes reception from all directions
other than that in which the beam is focused.
In the accompanying photographs we have some very interesting views of the micro-wave equipment which
is used to cope with just such a condition as mentioned above. This system is used to communicate across
the English Channel; one station is located in Lympne and the other in St. Inglevert. The distance between
the two stations is some 56 kilometers (about 35 miles).
In Fig. 1 we see the two enormous steel structures which support the transmitting and receiving station
forming one side of the circuit. The two parabolas which serve to focus the waves for transmission and
reception are mounted on the top of this steel structure. The parabolas are approximately 9 3/4 ft.
Fig. 2 - The micro-wave generator, which is located behind the parabolic reflector
shown in Fig. 3.
Fig. 4 - The master control room through which the different types of service are
Behind these parabolic mirrors is located the micro-wave generator tube and its associated controlling
circuits, these are shown in Fig. 2. Fig. 3 is the front view and in the center of the large parabola
is a small cup-shaped instrument which further aids in concentrating the focus of the transmitted wave
and this cup is supported by three large brackets as can be seen in the photograph.
In Fig. 4 we have a view of the control room through which can be routed the various types of traffic
which the system handles.
This circuit is one of the most versatile of any radio hook-up. Arrangements have been made for high
speed printing, regular Morse and radio-telephone communication. The entire system is automatic, insofar
as the power supply is concerned. Voltage regulators and other control devices are used to maintain
perfect uninterrupted communication. The transmitting system uses a regular modulator together with
the necessary amplifier stages in order to bring the voice or code up to a sufficient level for complete
The code and printing machines use an audio frequency tone-generator to supply the necessary modulation
An elaborate receiver is used wherein the incoming waves are changed to a frequency of approximately
300 kc. and then amplified through the intermediate frequency amplifier, finally detected and amplified
similar to the conventional superheterodyne.
The output of a receiver can be connected to either a teleprinting device which will print the incoming
signals or to an outside line for telephone communication. In other words, the entire installation takes
the place of telephone or telegraph cables which otherwise would be used to bridge the gap between the
two shores of the English Channel.
While we do not know of any truly micro-wave system such as this being installed in the United States,
we do have a very interesting installation and one which is very much similar in operation. This American
system was developed by the Bell Telephone Laboratories and it bridges Cape Cod Bay from Provincetown,
R.I. to Green Harbor, Mass.
Here too, due to the large expanse of water between, it was deemed more advisable to use a radio
communicating system rather than build a 25-mile telephone line. These transmitters and receivers operate
on a wavelength of 4.7 meters and are modern in every respect, inasmuch as a crystal-controlled master
oscillator amplifier circuit is employed. The receivers are modern superheterodynes, with the main oscillator
of the superhet receiver also crystal-controlled. This system is in use entirely for telephone work
and just replaces the ordinary phone circuit. Incoming telephone calls are routed through the radio
hook-up in the same manner as they would be if a land wire system were used.
The transmitters are mounted on the dependent upon the 100 ft. poles which were provided for this
purpose. The antennas are also mounted atop these poles and long transmission lines from the transmitters
to the antenna serve as the connecting link. This system is rather complex, in that they have a special
tone generator which operates at a frequency of 1000 cycles, interrupted at 20 cycles, for ringing the
operator at either end of the circuit. For instance, so modern is this equipment that the operator at
the central station at either end of the circuit can make checks upon the operating conditions of the
transmitters themselves. Twenty-four-hour-a-day service is provided and to date, faultless performance
has been maintained.
Posted March 2, 2017