could take this article from 1950 and substitute 'drone' for 'intercontinental
bomber' and it would do a good job of describing present-day capabilities
for global defense based on modern communications. Get a load of
the photo of an Air Force technician doing repair on a radar chassis
- using a Weller soldering gun! Compare that to today's method of
circuit repair that often requires a hot air tool, tweezers, and
an eye loupe. Actually, I can remember replacing fried resistors
in my USAF group's radar system using just such a soldering gun.
Most of the chassis had point-to-point connections where components
connected to bifurcated terminals or terminal tab strips. The Ground
Controlled Approach (GCA) mobile trailer pictured looks a lot like
the Equipment Trailer for our
, except the search radar antenna was larger. That
tall box on the left is a mechanically scanned x-band precision
approach radar (PAR) antenna for elevation; the azimuth antenna
is similar and lies horizontally lower on the trailer.
Graduated from the U. S. Military Academy in 1926 and commissioned
second lieutenant of Signal Corps. Attended Sheffield Scientific
School at Ya'e University receiving his MS in 1927. In June
of that year reported to Fort Monmouth where he served in various
capacitIes until he entered the company officers' course of
the Signal School in September 1928, which he completed a year
later. He subsequently served as an instructor in chemistry
and electricity at West Point where he remained for five years
except for a short period of study at Columbia University. He
held various commands during the war and in 1945 returned to
the United States to become air communications officer at Air
Force Headquarters in Washington. He served in other capacities
and received his present post in 1947.
By Major Gen. F. L. Ankenbrandt
Director of Communications,
Headquarters, U. S. Air Force
From take-off to "bombs
away" - at the flip of a switch - our giant global air armadas are
in constant contact with their headquarters.
In the few
years since the end of World War II the development of an aerial
concept of strategic national defense has presented the public with
a new family of terms - terms that inspire vision of a shrinking
globe and suggest the elimination of boundaries previously thought
insuperable. The sonic barrier has been penetrated and supersonic
speeds have been attained. We have devised aerial tankers for in-flight
refueling. We have indirectly brought every spot on the globe within
range of USAF strategic bombers. Concepts of tactics and strategy
have necessarily been revised to ensure that new capabilities are
exploited to the utmost.
Central to the concept and to the
revision of our strategy is the super-bomber - the intercontinental
land-based bomber that can deliver its bomb-load from a base in
this country to an enemy-held target anywhere in the world. This
bomber can pulverize an industrial target; it can support our Army;
it can eliminate the source of an attack directed against our Navy.
It is a weapon new to the history of warfare, and unique in its
application. The bomb-load it carries spreads destruction beyond
the capacity of any other weapon. Its range is unrestricted. It
introduces problems previously unknown to military strategists and
tacticians. But the principles directing its use are as old as warfare
itself, because they are the principles of command and control.
And command and control mean communications.
It makes little
difference to the commander of a strategic air force where his command
post is located as long as he is in communication with the aircraft
he dispatches. The world, to him, is an onion and the vast distances
that face a land or sea commander are just so many hours - or minutes
- in span. He can dispatch aircraft from a number of points in the
world to far-distant targets with almost push-button ease - but
when the aircraft are out of sight of their bases, does he still
have the command and control that was exercised in making them airborne?
Skilled technicians repair the USAF's electronic equipment.
If he has good ground-air radio communications, his command is extended
directly to the aircraft in flight and he can redirect it to alternate
targets or recall it to its base at will. However, if the communication
link to aircraft in flight cannot be established or maintained,
his command ends the instant the aircraft becomes airborne and the
aircraft is committed irrevocably to the destruction of the target,
regardless of sudden political changes that may make recall or diversion
a matter of grim urgency.
On paper, the problem of keeping
the strategic air commander in touch with his pilots is simple.
To illustrate, take a number of fixed points and draw a number of
radial lines in all directions at random. Draw another family of
lines across the radials at random to indicate the possible flight
paths of aircraft. The radials now are communications circuits.
Let's take a closer look at them.
Applying scale to our
drawing, we find that the circuits are from a few hundred to a few
thousand miles in length. We consult the frequency prediction charts
furnished by the Central Radio Propagation Laboratories and make
a series of calculations. The optimum working frequencies will vary
from about five to twenty megacycles depending upon which circuit
is selected, the time of day, and the distance from the station.
We select a frequency from the five, eight, twelve" eighteen, and
twenty megacycle bands and send them out to the half-dozen or so
ground stations associated with the relay stations of the main point-to-point
Now that our frequency problems seem
to be taken care of, let's pause a moment and examine the ground
plant. Making a tremendous arc around the globe somewhere between
thirty and sixty degrees north are a number of ground terminal stations
that form the main line. The circuits have a maximum capacity of
300,000 groups a day, and associated with each radioteletype tape-relay
facility is a high powered ground-air station capable of transmitting
simultaneously on three of the five selected frequencies. Modern,
professionally engineered, and capable, the lash-up seems foolproof
enough and we turn with confidence to an examination of the airborne
walk along the ramp to an actual terminal, admiring the sleek aerodynamic
shape that looms higher against the sky as we approach, our eyes
search for the familiar fixed-wire antenna and the fairlead with
its trailing antenna weight tucked tightly in the cup. But our eyes
search in vain. A closer inspection reveals no sign of insulators
A non-commissioned officer steps down a ladder
from the bomber and looks quizzically in our direction. "Sergeant,"
we ask, "where are the antennas?" The sergeant gives us that look
reserved for mere laymen and points at the wing that seems to reach
the vanishing point as we scan the trailing edge for the hitherto
invisible antenna array. "I'm afraid that you'll have to point it
out" we say in embarrassment, and the sergeant signals us to follow.
We walk in his wake to the tip of the wings. "That's the insulator
for the wing cap," he says with a pitying look.
"There's one just like it at the other end."
"Mind if we go inside and look at the radio operator's position
"It's all right I guess; anything special you want to
"Yes," we reply as the radio operator sergeant leads
the way into the cavernous interior, "everything."
sits down at a table and moves a headset to one side. At the back
of the table is a panel with a collection of unidentifiable knobs
and firmly attached to the table is the usual radiotelegraph key.
"Well" he says with a wave of his hand, "this is it."
where is the transmitter and receiver?"
The crew chief says
"In the wing though all you can see is a tank that looks more like
it holds gas or oil or something. Doesn't look like a radio set.
Anyhow, it works, wherever it is."
We smile a little to
ourselves as the sergeant goes on to explain that the radio set
and all of its immediate complexities have been removed from the
radio room and stored in some remote portion of the aircraft. The
maintenance section is responsible for keeping it a serviceable
set, but even so, the radio operator still has his hands full handling
his briefing folder (containing frequencies, propagation data, schedules,
and call signs) and the plain business of getting a message through.
Interior view of the Ground Controlled Approach equipment.
"I hear a rumor," the sergeant tells us, "that the 'long hairs have
cooked up a 'black-box' that will put me out of business one of
these days. Some gadget that prints the message on a roll of paper
- something simple enough for the co-pilot to operate."
"I wouldn't worry, sergeant," we assure him, "we can make 'black-boxes'
do everything but use common-sense. That's where the human element
"Right," says the sergeant; "'black-boxes' can
work out problems that would take me weeks, but when a channel's
jammed or the frequency predictions don't work out just right the
'black-box' just quits. A sharp radio operator won't quit until
he's got the message through."
We leave the aircraft trying
to absorb the effect of this airborne terminal station on the probabilities
of maintaining the chain of command between the Strategic Command
and this bomber once it becomes a striking force. The efficiency
of this airborne terminal is certainly far below that of the ground-air
station with its high-power, its high-gain directive antenna arrays,
its diversity reception, and its surface-level operating conditions.
The airborne radio operator, encumbered with clothing and protective
devices against the cold and low pressures of the sub-stratosphere
(in case cabin pressures are lost) certainly cannot be expected
to come up with the same degree of performance that another operator,
sitting at the control console of the ground-air station, can. Furthermore,
the airborne sergeant can't entirely free himself from certain anxieties
over the hours that he is airborne. The fatigue of his unrelieved
attention to his job mounts at a faster rate than that of the ground
operator who can say: "Hey, Joe, take my position for a minute,
I wanna run over and getta cuppa coffee."
We can't escape
the fact that the airborne operators of our strategic bomber force
loom up as the single element in the whole chain that must come
through with perfect performance against heavy odds. But now that
we are acquainted with the problem and the mechanisms involved,
let's look at the conditions that the airborne sergeant will have
to surmount before he can assure us that the command line is intact.
Because of the distances involved, he must use frequencies
from the congested - and somewhat irresponsible - high frequency
band. The properties of the band permit us to make an educated guess
as to what frequencies will be the most suitable for a given path
at various times of day and night. However, when we consult the
"Berne Book" to see what other countries may be using our choice
of frequencies, and monitor the channel for a firsthand survey
of users, the call signs we hear somehow or other don't coincide
with Berne listings. The conviction dawns on us that at some other
point in space, where we have no monitoring stations the interference
pattern may be substantially different.
A glance at the
world map and its present political divisions is proof enough that
large land masses of the world under a single political philosophy
can only be controlled by high-powered ground point-to-point radio
communications circuits. Industrial developments require high-traffic-capacity
communications, and when that nation is at war the civil and military
communications requirements will exhaust almost every communications
channel in the high frequency band. Even though certain countries
may not subscribe to international agreements, in peacetime, at
least, they must operate their circuits on a "live-and-let-live"
basis or there will be hopeless confusion.
Not only are
the big powers a source of congestion. A host of smaller nations
have been urged to develop, and the United States has provided them
with high-frequency radio communications and broadcasting equipment,
and we have seen to it that they have frequencies for its use. Furthermore,
the vast quantity of radio frequencies required for the United States
military forces in all parts of the world will further burden the
capacity of the high frequency band in providing usable channels.
As a mitigating factor to the apparently hopeless situation,
a further study of the radio propagation charts shows that if a
number of stations throughout the world are transmitting simultaneously
on the same frequency (which they certainly are) they will not necessarily
be all heard at a given point at the same time. Short-wave listeners
and radio amateurs can verify this phenomenon. It is not at all
unusual to hear a radio amateur say:
Exterior view of the Ground Controlled Approach equipment.
"That's funny - last night at this time the Aussies were booming
in, now all I can pick up is South American stations." These anomalies
of the high-frequency band are in our favor, though one can be certain
that some interference can be anticipated. Our ability to work through
that interference will depend upon the personal skill of the airborne
operator and the quality of the receiving equipment he operates.
If he can get his own signal just a few hundred cycles away
from the interference (depending upon its modulation or bandwidth)
he can slice away the signal completely. Except for outright jamming,
he has a good chance of getting a message out of the hash that meets
his ear when he switches to a new channel and listens out for his
Let us now follow through on a mission and see
how well the system works.
Let us imagine that unannounced
aggression has committed us to war and a message from the Joint
Chiefs of Staff arrives, directing that proper measures be taken
by the Strategic Air Force commander in carrying out an effort to
insure our defense and end the aggression. Simultaneously, from
a number of vastly separated points bombers must take to the air
and fly to targets in the enemy's heartland and on his perimeter.
The first bomb release is four hours away.
At this instant
a flash message is delivered to the commander. A country in alliance
with the aggressor has broken its ties with the enemy power in the
face of potential bombing attacks, and all targets within its borders
must be immediately deleted from the current list of priorities.
On the situation map is a steadily lengthening line reaching from
the base from which our counter attacking planes were launched to
the industrial capital of the now unshackled country. Slicing through
the sub-stratosphere, and closing in rapidly upon this country that
has sued for peace, is an aircraft capable of indescribable harm
unless it is diverted or recalled.
A diversion message with
"FLASH" precedence is placed on the main communications axis and
addressed to the aircraft. The message is converted to perforated
tape and is transmitted outward along the main line from tape-relay
station to tape-relay station, branching off to a ground-air facility
at key points where it is passed to the operator on duty.
A ground operator takes the message from the hands of the supervisor.
When he sees the precedence, the paper suddenly feels hot to the
touch. He clips it in front of his position and hurriedly consults
the frequency plan that was transmitted with the mission order a
few minutes earlier and presses a lever on the intercom. "Hey, Joe
- Charlie - get this! - put transmitters four, five, and seven on
the antenna that covers zone 'B.' This is it!"
the three transmitters in on frequencies that for the next two hours
the airborne operator will be guarding in succession, and starts
transmitting the call-sign followed by the message. He repeats,
and repeats again. When transmission has been completed the ground
operator logs the message and listens out. In a minute or so he
will be able to hear another ground operator repeating the transmission
from a point a little further along the axis of communications.
On the mission, in the aircraft, the airborne operator is
keeping an eye on the clock for frequency changes in accordance
with his briefing chart. As he makes his first shift at the appointed
time, he hears his call sign deep down in the "hash." He rapidly
shifts back to his previous frequency and can barely make out his
signal in the noise. He shifts up again to the previous channel
and turns his receiver to "sharp" reception. He fishes around a
moment then hears his call-sign coming in loud and clear.
He copies the message the first time over and waits for the
repeat to verify the text and the authentication. He consults his
code book. No, this is no enemy decoy message, it's the real thing.
He acknowledges the message and switches the intercom to "call"
to pass the message to the aircraft commander.
of miles away in the operations room of the Strategic Air Force
commander the line on the map showing the progress of the bomber
from base toward target is now dog-legged toward the secondary target
assigned to this aircraft.
The worried Intelligence Officer
wrinkles his forehead and mutters, "Well, he got it; there'd have
been hell to pay if he hadn't."
Yes, there'd have been hell
to pay if he hadn't. These bombers pack a punch - the Sunday punch.
And command has to stretch all of the way - clear to the instant
of bomb release. But the message has been put through. The airborne
operator has functioned more reliably than any little black-box.
He had transmitted to the pilot the change in order of the strategic
air commander, communicated over the ground-air radio.
Liaison Set Development
After the close
of World War II the U. S. Air Force began concentrating great effort
toward providing aircrews with the improved radio communications
equipments which were so sorely needed.
Queries were sent
out to all operational agencies asking for comments on the weaknesses"
of existing equipments and a statement of desires in improving radio
sets. The replies seemed at first to be demanding the impossible
but careful evaluation disclosed many major deficiencies in the
currently standard equipments.
Of all the radio communications
equipments presented for scrutiny, the liaison set provoked the
greatest comment - much of which may have been interpreted as a
scathing denunciation. There seemed to be little about it that was
right. Although it was a substantial advance over its predecessor,
it was a far cry from what could be considered the ideal set.
A recap of the criticisms revealed that they all came to
focus at one point: it was not possible to train radio operators
to the required degree of proficiency in the limited time available
between induction and assignment to a combat aircrew. In other words,
aircraft manufacturers could produce radio operator positions in
heavy aircraft faster than we could man them. It was difficult enough
to teach operators the Morse Code, combined Communications Procedures,
radio circuit discipline, and communications security, but when
he was placed in front of his liaison radio equipment, the profusion
of knobs and switches proved to be just so many statistical opportunities
The plotting board at the USAF Radar Approach Control center.
The radio operator had already been relieved of as many of the knob
settings as was possible. The maintenance crews had set up the preset
frequencies in the storage mechanisms of the ten-channel transmitter,
leaving him only the task of tuning the antenna circuits, a task
that accounted for frequent communications failures. His receiver
was a bandswitching, "coffee-grinder tuning" equipment containing
sufficient permutations and combinations of operator-error to account
for additional communications failures when the requisite skills
were missing., "coffee-grinder tuning" equipment containing sufficient
permutations and combinations of operator-error to account for additional
communications failures when the requisite skills were missing.
"Give us a set," pleaded the tactical operators, "where
the operator turns it on, sets the exact frequency in a window,
and starts beating the key, knowing that his transmitter and receiver
frequency could be used for calibrating WWV." "Make the antenna
tuning automatic," echoed others, "regardless of whether he's on
the fixed-wire or trailing antenna." "Let him store up at least
twenty frequencies so that he can QSY within a few seconds to another
assigned channel." "Take all of the knobs away from him but a channel
selector and a volume control." "Make it so simple that a pilot
can operate it."
Five years have gone by since the new liaison
set was visualized by the operational commands and several hundred
man-years have been expended in developments and monitoring activities.
The needs of the two services having major interest, the USAF and
the USN, have been combined in Joint Military Characteristics and
each service has engaged in separate developments - all with the
aim of providing a single, jointly standard liaison radio equipment.
The products of these separate developments are nearing the evaluation
stage - both having demonstrated that the ideals expressed by the
operational commands were attainable. True, there were compromises.
Neither of the developments could meet the desired weights or QSY
times - and the cost of attaining some of the ideals has caused
some last-minute soul-searching on the part of the operational commands.
The sets are not simple. As a criterion, let's consider
the number of tubes as an index of complexity. The present USAF
standard liaison radio set, AN/ARC-8, contains 23 vacuum tubes.
The several developments currently assessable contain 54, 86, and
137 vacuum tubes respectively. Just how much of the automatic operation
should be accepted, and how much could be given back to the intelligence
of the radio operator with a net saving in circuit complexity?
Representatives of the major USAF commands were invited
to observe the detailed functioning of the 137-tube development
and the questions were propounded. "Here is the set you've dreamed
about" they were told, "you've seen it perform in accordance with
your desire of five years ago. We can save a lot of tubes and complex
circuits here and there by giving some of the tasks back to the
radio operator. Just which of the automatic functions do you feel
that you can dispense with ?"
Generals turned to confer
with their specialists. Radio operators looked at each other quizzically.
Engineers looked expectantly for a sign of weakness - for some indication
that the operational personnel were appalled with the complexity
of frequency synthesizers, were suspicious of mechanical brains,
or were skeptical that the set could function under service conditions.
A hand went up tentatively.
"I don't think the channel-storage
function is absolutely necessary," one general observed. "As a matter
of fact, I like the idea of the radio operator being 'frequency-conscious'
rather than 'channel-number-conscious.' "
"We like the channel-storage
feature," said a representative of another command, "most of our
frequencies are firm assignments and they can all be set in."
When the comments from the USAF representation were analyzed,
it became clear that no one was willing to forego any of the automatic
features, that the suggestions and comments were for additional
features and advances. They would like to have a flexible liaison
radio set that would answer any of the requirements of the
operational commands without interfering with the ideal of interchangeability
of major components. Even when the engineers made little pleas for
the relaxation of certain demands, they were received coldly. The
concept of a fully automatic liaison radio sat rather well with
the operators in spite of the increased dependence upon tubes and
integrity of circuit components.
As an innovation in the
unveiling of a new development, the maintenance activities were
given an opportunity to assess the impact of such a complex device
upon the various echelons from the squadrons to the major repair
depots. The representatives of Training Command came to the alert.
Just how could a man - an ordinary man - be trained to find the
source of a malfunction in such a complicated mechanism within his
"Maintenance of this equipment," began the
speaker, "is divided up into three echelons - the organizational,
the field, and the depot." As the narrative of maintenance actions
unfolded, the Training Command representatives relaxed in their
chairs. What had appeared as an insurmountable difficulty now was
as simple as A, B, C - the equipment was designed so that it would
practically maintain itself - at least, it is possible for a uniformed
lad to take a simple test set and be guided unerringly to a faulty
section of the transceiver. Employing a number of "go-no go" tests,
the organizational mechanic would isolate a faulty removable section
and replace it on the spot, placing the set back in service within
the hour. The faulty chassis would be sent to the field repair shops
where additional test equipment would single out the faulty sub-assembly,
allowing the return of a serviceable section back to the organizational
supply shelves within the day. In neither case was it necessary
to heat up a soldering iron. The sub-assemblies are divided up into
two categories: those capable of economical repair and those to
be thrown away. The former are returned to the rear areas for depot
repair. It seems at first glance that the maintenance activities
have simply unloaded their problem onto the already sagging shoulders
of the supply organization, however, upon arrival at a realistic
level of supplies to be maintained at each echelon, the problem
of "not-in-stock" disruption of maintenance operations appears surmountable.
Now that an acceptable piece of hardware appears to be within
the capabilities of industry, the whole problem of liaison radio
communications is in need of review. The existing developments have
produced an equipment that has relieved the radio operator of certain
skills that are purely apart from his basic skill of transmitting
and receiving intelligence with the dots and dashes of the Morse
Code. The time available for his training in these respects is still
too short to provide the required degree of proficiency. In the
last war, the greatest fault was poor radio discipline - radio operators
were under such compulsion to get their own messages through that
they transmitted out of turn and caused interference to other aircraft
or ground stations by persistent calling. Code speeds were those
of the slowest operator - too slow, in fact, to permit clearing
the transmissions of several aircraft within a short space of time.
An attempt was made to relieve congestion by permitting only the
lead aircraft of a formation to transmit operational messages, screening
the organizations for the most accomplished operators and assigning
them to lead crews. This, of course, caused a deterioration of interest
on the part of the remaining operators and they found themselves
so far down in proficiency when an emergency did arise that they
were unable to place the radio equipment on the air and establish
communication with navigation or rescue agencies.
experienced in attaining our aspirations in radio transmitting and
receiving equipment led us also to believe that the problems of
the radio operator could be solved by employing some "visual message
presentation system" for transmission and reception of the intelligence
contained in a purely operational message. Numerous systems were
reviewed against the stated objective of a three to six thousand
mile transmission path and each was found to be considerably less
than automatic. Considered were standard teletype, facsimile, telautograph,
lighted "marble-board" panels, and specialized printing systems.
There was one insuperable difficulty. In spite of CRPL assistance
in determining optimum working frequencies, there remained propagation
phenomena such as selective fading and multi-path reception, as
well as a hopelessly congested high frequency spectrum. Who was
to "clear" the channels needed for printing systems that can't tolerate
radio interference? Who was to predict in advance of a flight the
channels that could be presumed to be free of interference at various
geographical points far removed from monitoring stations? When would
the optimum frequencies be so cluttered with multi-path reception
that teletype or facsimile would be out of the question. It seems
hopeless to design a machine with the intelligence of a trained
c.w. operator - a machine that can selectively "listen" to a desired
signal to the exclusion of all others present and put down on paper
the desired intelligence and none other.
of our point-to-point communications activities was consulted for
a solution. It was found that in spite of a constant transmission
path, use of optimum frequencies, erection of large directive antenna
arrays, employment of high power, and operation by personnel of
skill and experience, there was a constant level of unpredictable
and unscheduled circuit outage. Take away from the fixed communications
station its constant path, its optimum frequency, its efficient
antenna system, its high power, and experienced maintenance attendants
and you have the equivalent of an airborne communications terminal.
It can be seen that the probabilities of an aircraft, say, at three
thousand miles from its ground station, making an initial unscheduled
contact employing radioteletype or facsimile is remote indeed. Consequently,
for the time being until a suitable system comes along, we are still
considering c.w. as the primary emission from the liaison radio
equipment. Secondarily, for certain specialized applications, it
appears that teletype and facsimile show promise, however, for ranges
up to six thousand miles, nothing is in sight that can compete with
manual radiotelegraphy that is adaptable to the airborne radio installation.
As a result of this conclusion, attention was redirected
toward the development liaison radio set with the aim of tightening
up the c.w. features and reviewing its capabilities for this method
of communication. The transmitter was found to be at the highest
state of development as a radiotelegraph set, having the capabilities
of a secondary frequency standard in accuracy and stability. With
the aid of automatic antenna tuning systems, it could deliver the
maximum amount of available power to the antenna, whether fixed
wire, wing-cap, or trailing wire. The emission was pure c.w. with
no spurious components or frequency modulation. A study of the receiver
showed room for improvement. In the initial form it was - in accordance
with the military characteristics - a simple, straightforward receiver
(embodying refinements, of course) using the usual beat-frequency
oscillator "C.W.-Tone" control. The frequency accuracy was the same
as the transmitter (being slaved to the same synthesizer) but the
normal passband placed a lot of emphasis upon the skill of the radio
operator in reading his desired signal through interference. It
appeared that some improvement could be made in the rejection of
unwanted signals by inserting the narrowest possible passband in
the receiver output, permitting the radio operator to slice away
on interfering signal even though it was only 500 cycles removed
from the desired signal. The "C.W.-Tone" control then became the
"Fine-Tune" control, allowing the radio operator some latitude in
netting with stations that haven't the frequency accuracy or stability
of the liaison set. Fortunately, the "C.W.-Slot" idea of adjacent
channel rejectivityywas attained without adding a single extra control,
thus staying within the basic philosophy of a minimum of knobs and
switches.was attained without adding a single extra control, thus
staying within the basic philosophy of a minimum of knobs and switches.
Considering the liaison set for c.w. communications, certain
features begin to take on importance - features that are available
for the first time in military communications history. The first,
that of frequency stability and accuracy, permits an altogether
new concept in netting a number of scattered airborne communications
terminals with a group of ground stations on the same frequency.
In the first place, there is no possibility of off-frequency operation
- a contingency that has plagued us from the beginning- and a listening
station employing a receiver of the same accuracy and stability
as the airborne liaison set can receive transmissions from any number
of aircraft without necessity of making readjustments in tuning
to accommodate variations in frequency from one aircraft to another.
All aircraft on a given frequency will practically "zero-beat" with
one another. This will require radio discipline of a higher order
than ever achieved previously since the ground operator will no
longer be able to separate two interfering signals by taking advantage
of slight frequency inaccuracies between two aircraft calling at
the same time. The signals will be inseparable and both will be
unreadable. On the credit side of the ledger is the fact that no
longer can there be a missed contact caused by an airborne liaison
set being off-frequency just enough to fall outside of the passband
of the monitoring station receiver. He will be heard in exactly
the same tuning position as all previous aircraft on the same channel.
As a corollary, of course, ground station receiving equipment must
have tuning accuracy and stability adequate to long channel guards
on a given frequency without drift or inaccurate setting. Since
the airborne liaison radio receiver will have a "broad" position
for monitoring and a "fine tune" range of about plus or minus three
kilocycles for any given channel setting, netability with existing
ground transmitting equipment is assured even when using the narrow
There will be no further necessity for long
call-ups or tuning transmissions with this degree of frequency accuracy
nor any necessity of making constant fine adjustments because of
receiver oscillator drift. The radio operator will be freed of any
adjustments to transmitter or receiver other than selecting a frequency,
putting the desired signal in the "slot," and adjusting the volume
to a comfortable level. It is altogether conceivable that he will
never see any part of the transceiver or antenna - all of his operations
being conducted from a control box no larger than a folded pocket-handkerchief.
Until the sets are out of development it is not possible
to reveal more of the details, but the feeling is shared in all
quarters that the substantial advances in liaison set communications
have been attained at a respectable cost and will soon be released
to the field.
We used to say that "communications is a function
of command." Now we may well say: "Communications is command."