May 1945 Radio-Craft
Wax nostalgic about and learn from the history of early electronics.
See articles from Radio-Craft,
published 1929 - 1953. All copyrights are hereby acknowledged.
Seamless integration of wireless
communications with wired communications has not always been a yawn in technical
strategy discussions. It has really only been since the early 1990s with the introduction
of ubiquitous cellphone systems that someone on a wireless device could connect
directly with a wired (i.e., landline) contact and not need an intermediary operator
to facilitate. Some military communications, the Inmarsat system, and a few other proprietary
systems were available, but not to the public at large. This article reports on
some of the Army's early attempts at implementing wireless-to-wired communications,
specifically as implemented during the Normandy Invasion on
D-Day. Unlike present day
systems that rely heavily on data compression and massive multiplexing, those systems
allocated the standard audio (voice) bandwidth to each channel.
How many of us can remember how nice it used to be when we could carry on a telephone
conversation and not suffer the annoyance of momentary dropouts and system delays
that are sometimes so bad that it is almost necessary to go back to the old WWII
radio era "over" declaration at the end of each sentence so the person on the other
end would know it is OK to start talking?
Army Radio Communications
How the relay link sets were employed in the Normandy invasion.
The central relay station is two terminal sets placed back-to-back.
Although the Army's basic policy considers wire to be the primary means of communication,
and radio the secondary means, the very nature of this war with its highly mobile
forces deployed throughout the world has placed ever increasing emphasis upon radio
as the primary means for communications with highly mobile elements such as aircraft,
tanks, amphibious vehicles and assault troops, or across enemy held territory and
over water and terrain inaccessible to wire line construction. Radio must provide
a degree of service comparable to that of a wire facility, including when necessary,
the capability of being tied in with existing wire circuits to form one system giving
the same grade of service as the wire system.
One of the outstanding developments of this war in Military Communications is
the Army's VRF Radio Relay System which provides a true integration of wire and
radio circuits into a single system or may be used as a separate system in much
the same manner as the wire circuits.
The heart of this system is the broad band FM radio set, designated AN/TRC-1
developed by the Camp Coles Signal Laboratory of the Signal Corps Ground Signal
Agency with the collaboration of the Link Radio Corporation. This set is capable
of operation either as a terminal of a radio circuit or as an automatic radio relay
set between the two terminals of a radio circuit in extending the overall communication
range beyond the distance range of an individual radio set.
It is used in conjunction with the Army's telephone "spiral-four" carrier cable
system which provides the practicable terminal equipment whereby a radio circuit
can be integrated with the wire circuit, or substituted therefore, in whole or in
part, as the necessity dictates.
Fig. 1 shows a simplified functional diagram of a complete multichannel
VHF radio relay communication system. The telephone and telegraph terminal equipment
CF-1 and CF-2 is common to both the radio system and the "spiral-four" wire system.
The radio terminal set is connected to its associated telephone terminal by "spiral-four"
cable up to approximately 15 miles in length, one pair of the cable being used for
transmitting and the other pair for receiving. The radio relay sets comprising in
effect two radio terminal sets connected back-to-back are substituted for the telephone
repeaters of a wire system. Duplex operation is achieved by the use of separate
receiving and transmitting frequencies at each radio set.
Fig. 1 - A typical army network, in which wire lines, carrier
channels and VHF radio circuits are combined in a large multi-channel system.
Four telephone channels, each approximately 2800 cycles wide, within an audio
frequency band of 200 to 12,000 cycles are obtained from the Telephone Terminal
CF-1. Channel 1, operating at voice frequencies, is normally used as an order channel
for intercommunication between terminals and relay sets for supervision and line-up
purposes within the system. Each radio set is equipped with filters to confine the
order channel to the band 200 to 3000 cycles and prevent mutual interference with
the carrier frequency channels. Ringing over the individual telephone channels is
accomplished from field telephones or switchboards by the use of voice frequency
ringers which provide a 1000-cycle tone modulated by the 20-cycle telephone ringer.
Tone teletype channels may be provided over anyone telephone channel by the connection
of the Telegraph Terminal CF-2 thereto. Additional teletype channels may be applied
in like manner to other telephone channels. Facsimile service may be obtained by
the use of Facsimile Equipment RC-120 on anyone or more of the telephone channels.
The principal characteristics of the radio receiver and transmitter are: (1)
a horizontal three-element antenna array comprising a driven dipole fed by a 50-ohm
flexible solid dielectric coaxial transmission line and parasitically excited reflector
and director dipoles, all adjustable in length to the operating frequency and supported
on a mast head by a 40-foot sectional steel tube mast; (2) a 2500-watt, 115-volt,
60-cycle, gasoline engine driven generator.
A 250-watt radio frequency amplifier is available as auxiliary equipment for
use with the 50-watt radio transmitter to increase signal strength over unusually
long or noisy transmission paths, where high power is advantageous.
Fig. 2 - Comparison, wire and VHF communication facilities,
U.S. Army multi-channel systems.
On the second day after the initial landing on the Normandy coast, the cross-channel
circuit illustrated above began operation, providing initially facsimile transmission
of air reconnaissance information on military objectives from a Tactical Air Command
Headquarters to the invasion forces. Shortly thereafter full multichannel telephone
and teletype facilities were provided from Central Headquarters in England to the
field commanders of the First U. S. Army in France. Following these outstanding
uses, other armies, as they became operational on the continent, extended similar
multi-channel radio facilities to their Corps, from their Corps to Divisions and
between Corps within each army. The Air Forces likewise linked their base command
establishments by means of similar radio circuits providing the establishment of
equivalent wire circuits.
As the Armed Forces progressed across France additional radio relay facilities
were established for both tactical requirements in the forward areas, and for administrative
purposes in the rear Communication Zone. With the installation of additional cross-channel
facilities, and of wire lines and other radio circuits on the continent, the radio
relay systems became part of a completely integrated and comprehensive network of
telephone, teletype and telegraph circuits covering an area in Europe equivalent
in size to that from New York to Chicago and from Detroit to Atlanta. Through this
integration, the radio systems became vital links in the network in providing primary
circuits under enemy fire which took prohibitive toll of lives and material during
attempted wire installations, or over terrain impassable to wire lines; and also
emergency circuits in the event of traffic overloads or failures of other facilities.
In citing the importance of this equipment as an emergency facility during a
failure of the main cable system across France as a result of combat operations,
the Chief Signal Officer, Major General W. Rumbough, European Theater of Operations,
stated, "In spite of this very serious cable interruption, and I do not think any
single trouble could have been worse, we handled 2709 messages -, that is nearly
2 messages per minute throughout the 24 hours."
The logistical advantages accruing from the use of radio relay communication
system over the "spiral-four" cable system, as illustrated in Fig. 2, have
been the principal factors through which this type of equipment has achieved its
favorable reception and praise in relieving transportation. installation and maintenance
problems. Greatly expanded commercial use of the principles for post-war applications
Wire Communication System
1. Approximately 94 ship-tons of equipment required for a fixed system length
of 100 miles.
2. Requires large force of men and materials for installation and maintenance.
2. Subject to interruption from enemy action, equipment failure, and electrical
interference at an infinite number of points along cable route.
4. Not suitable for transmission over large bodies of water or territory
controlled by the enemy.
Radio Communication System
1. Approximately 25 ship-tons of equipment required for a system length of 100
miles in average terrain. Indicated number of radio relay sets may be reduced, or
system length may be increased without additional equipment, when radio sets are
installed on high elevations which afford long transmission paths (without greatly
exceeding line-of-sight) between stations.
2. Installed, operated and maintained by a small force of men without special
equipment or materials.
3. Subject to interruption from enemy action, equipment failure and radio
interference at 5 points only.
4. Well adopted for transmission over reasonably large bodies of water or
portions of territory controlled by the enemy.
Posted May 19, 2023
(updated from original post