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
MPN-14 search radar system
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.
Why, Strategic Air Communications
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
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.
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 communications axis.
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 terminal.
We 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 or sky-wires.
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 see?"
"Yes," we reply as the radio operator sergeant leads the way
into the cavernous interior, "everything."
The sergeant 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."
"But where is the transmitter
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 comes in."
"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."
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
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 call sign.
Let us now follow through on a mission and see how well the
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.
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
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!"
He dials 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.
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
Thousands 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 for error.
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."
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.
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.
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
major 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 own lifetime?
"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.
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.
The success 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.
The experience 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 "C.W.-Slot."
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."