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 comms, 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
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.
Fig. 1 - A typical army network, in which
wire lines, carrier channels and VHF radio circuits are combined
in a large multi-channel system.
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.
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
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 are indicated.
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
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 December 17, 2014