The FCC's Radio Intelligence Division
October 1944 Radio News

October 1944 Radio News

[Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio & Television News, published 1919-1959. All copyrights hereby acknowledged. Special Insert: Radio-Electronic Engineering Department

According to an FCC document "11th Annual Report, Federal Communications Commission, Fiscal Year Ended June 30, 1945," Chapter VIII - War Activities, "The Radio Intelligence Division, established in 1940 to give America wartime protection from misuse of the ether lanes by spies or other illegal operators, discovered 46 unlicensed stations during the fiscal year, investigated 1,445 complaints of suspicious transmission and of interference. These complaints were received from the general public, commercial communication companies, Government agencies, and the military. During the year, the RID furnished fixes to 283 planes which were in distress. A total of 996 requests for assistance of all types to planes was received. The RID took 85,031 bearings. A number of alerts originated totaled 25,000. This figure represents the number of instances in which an origination was made by each monitoring station equipped with long-range, high-frequency direction-finding facilities for the purpose of obtaining synchronized bearings from a net of direction finding stations upon a particular radio station under surveillance. To facilitate its task of identifying the thousands of stations heard around the world so that the enemy, subversive or unlicensed stations may be spotted instantly, the RID compiled an additional 200,000 index cards for its files. These records show the operating characteristics of stations logged or otherwise monitored. In accordance with a budget reduction, the personnel of the RID was reduced from 468 to 328. The number of secondary stations was reduced from 59 to 28, of which 13 were equipped with long-range, high-frequency Adcock type radio-direction finders. The number of primary stations, totaling 12, was maintained." See also "The FCC's RID and Japan's Surrender."

Radio Intelligence

By Oliver Read, W9ETI

Managing Editor, Radio News

An eye-witness report on the little known technical aspects of the RID.

The Radio Intelligence Division (RID) of the Federal Communications Commission is one of the government agencies least known to the American public. Up to the present time little information has been forthcoming showing the important functions of this non-military unit. Highly important in peace - the RID has been performing one of the most essential tasks in wartime - ridding this country of illegally-operated radio stations, most of them by spies of foreign powers. Furthermore, they have saved hundreds of lives by locating lost aircraft. Millions of dollars worth of vitally needed planes have also been saved from an untimely crack-up.

The RID was organized several years ago by George Sterling, W3DF, who still directs all activities as Chief. Assisting in this important work are Charles Ellert, W3LO and Stacy Norman, W70K, all prominent radio amateurs.

Principal functions of the RID include: Maintaining a continuous policing of the entire radio spectrum to insure against unlicensed transmissions and taking appropriate action to suppress such operation; locating and eliminating interference to licensed stations; maintaining a continuous surveillance of licensed stations in cooperation with the Field Division of the Engineering Department, FCC; making intercepts of foreign non-military radiotelegraph traffic for the use of other civilian agencies of the Government, and recording foreign broadcasts for the Commission's Foreign Broadcast Intelligence Service.

Other important activities are performed by the members of the RID. Included are the rendering of emergency direction finding service to civilian and military aircraft, training personnel in radio intelligence work for other Government departments and foreign countries, and the furnishing of equipment to various Government departments, etc. The RID is comprised of twelve primary monitoring stations and thirty-two secondary monitoring stations located throughout the United States, its territories and possessions. All of the primary stations and secondary stations within the United States and all the secondary stations in the territories are linked together for instantaneous communications either by private tieline or by radio links. The activities of the monitoring stations is coordinated from three Radio Intelligence Centers. Work on the East Coast is coordinated from the Center in Washington, D.C., work on the West Coast from the Center at San Leandro, near San Francisco, and work in Hawaii from the Center in Honolulu. Each of the primary monitoring stations is located on a large tract of land to permit erection of extensive receiving antennas. These stations are also located so as to be as far away as possible from electrical interference which would be experienced in or near cities.

A typical primary monitoring station, located near Allegan, Michigan, was visited by the editors of Radio News in order to get firsthand information on its activities and to meet the personnel of the RID. Supervising at Allegan is William J. Hoffert, W5HVB and his assistant, Kenneth W. Miller, W5AOC. We found that 90% of the personnel at Allegan were licensed amateurs. Their experience had given them a valuable background for this important work. The personnel in the RID Division of the FCC at this station includes four monitoring officers and twelve operators. Working in shifts, these men "patrol the ether" twenty-four hours a day.

Associated with each primary station are a number of satellite stations known as secondary stations. Location of these are chosen with regard to density of population and radio activity. They are situated on leased property at locations that permit good radio reception, the great majority of them being within the continental United States.

In addition, there are associated with each secondary station one or more special mobile units that are equipped with radio receivers, equipment for taking radio bearings at short range, and equipment for recording the radio signals which are intercepted. At times, two or more of these mobile units work together on a particular case. For the purpose of coordinating their work many of them are equipped with radio to communicate with each other.

It is interesting to note that practically all of the equipment at the RID stations is in continuous operation. Mr. Hoffert pointed out, for example, that none of the receivers had required a major repair since they were installed in 1941. The equipment used at this station is typical of that used in all RID stations. In the "Cruising Room," for example, are one Bendix frequency standard; six Hallicrafters SX-28 and one S-27 receivers; one Hallicrafters HT-7 frequency standard; one National 1-10 receiver and one RCA 10kc. inverter with demodulator. In addition are the regular teletype-writers and emergency radio channels used for communications should the teletype fail. The operators in this cruising room tune the entire radio spectrum continuously in their search for unidentified signals. An Intercom connects to the two Adcock direction finders. This is used to "alert" the DF operator when a long-range bearing is required.

When it is necessary to report unidentified intelligence, operators in the "Intercept Room" record the transmissions on ink recorders, discs or cylinders. Equipment in this room includes a Bohme ink recorder, seven Hallicrafters SX-28 receivers, two Memovox recorders, Telecord wax cylinder machine and a Telrad frequency standard. A special receiver designated as SSR-202 (SX-28 with additional i.f. channel) is employed. This latter unit is capable of separating badly scrambled transmissions and by the use of special circuits (restricted at the moment) are able to bring in these signals clearly for recording.

There are six crystal-controlled standby frequencies always available. A Transmitter House far from the main building houses three RCA ET-8019 200 watt transmitters. These are operated by remote control from the Cruising Room. An Onan 5KW gasoline-driven generator supplies power to the transmitters in case of failure of the 60 cycle line supply.

We mentioned before that it is the job of the RID to police the entire radio spectrum. In order to detect subversive or other illegal use of radio it is necessary for the monitors at all of the stations to maintain continuous patrol of the ether. These monitors must be able readily to identify the hundreds of thousands of radio signals which they hear daily. There are a number of means by which radio signals can be identified. For example, checking call letters, checking frequencies, checking operating procedures, analyzing the traffic and analyzing technical characteristics of the signal, such as its strength, hum, echo, fading, and the particular style of the operator.

If it is still not possible to identify a signal by the application of these or similar criteria, it then becomes necessary to search and locate the transmitter by means of radio direction finding.

The RID stations make use of a highly perfected direction finder designed from the principles discovered by the Englishman, Adcock. It is known as a balanced H type and is shown on page 25.

A simple analogy to show how this direction finder operates would be the familiar battery operated portable radio set in a carrying case. These receivers use a built-in "loop" for picking up the signal. The loop consists of a number of turns of wire wound on a narrow rectangular framework usually fastened within the carrying case, and in some cases, mounted on the outside but always in a vertical position. Our readers are familiar with the fact that such a receiver has marked directional properties and that some stations are heard with much greater signal strength than others. These discriminations against a certain station may be altered by changing the position of the loop. This is basically the function of the direction finder.

If a pointer is attached to the loop and is made to traverse a circular scale graduated in degrees (marked from 0 to 360 degrees) it is possible to ascertain the true direction of a given radio station by noting the position of the pointer with reference to the scale when a null is obtained. This null is the point where the signal is no longer heard and occurs when the loop is "broadside" to the arrival of the signal.

In using a loop direction finder, the scale reading opposite the pointer is determined not only by the direction of the radio station with respect to the location of the loop but also by the position of the zero graduation on the circular scale. If the zero mark or graduation is placed so that it coincides with true north (which can be done either by revolving the scale or the object to which it is fastened) then the radio bearing obtained will be with reference to true north. It is advantageous to do this because the radio bearing can then be projected on a suitable chart or map in much the same manner as plotting a ship's course.

If only one direction finder is used, there is no way to ascertain the exact point on the projected bearing line which would correspond with the location of the radio transmitter. However, if an additional direction finder is used so as to provide a bearing from a different location, and this bearing was drawn on the map, then the intersection between the first and second bearing lines will correspond to the radio transmitter location. This is so because there can be only one common point between two straight lines, namely, at the intersection. The point of intersection between two such projected radio bearings is called a radio "fix." One direction finder could be moved about to provide two or more bearings; however, this process is too slow for obtaining a fix when time is important.

Even with the very best direction finders, the precision with which a radio bearing can be obtained is seldom better than 1 degree. In other words, the observed radio bearing may differ from the true or correct bearing by the amount mentioned. Among radio direction finder technicians this degree of precision in equipment performance is often referred to as an accuracy of plus or minus 1 degree. Precision is an important factor in selecting direction finder locations because it directly affects the accuracy of a radio fix which is one of the basic considerations in the evaluation of radio bearings.

When dealing with three radio bearings, the inaccuracy in the individual bearing causes the radio fix not to appear as a one point intersection of three lines but as a triangular area often referred to as a "cocked hat." If the direction finders are poorly placed, the area encompassed by this "cocked hat" may be large and the ability to estimate the position of the radio fix becomes most difficult. Reference to the charts will show that in the case of a two bearing fix and that if either has even 1 degree error, the point of intersection of the projected bearing would shift greatly due to the small angle formed by the bearing lines. It can be shown mathematically and, in fact, it is fairly obvious, that for a given bearing inaccuracy the determination of the radio fix is subject to the least error if the radio bearing lines intersect at an approximate right angle of 90 degrees. The size or the extent of the area enclosed by the "cocked hat," formed by the projection of three radio bearings, is no indication as to the probable accuracy of the radio fix. If two or all three of the bearings are subject to observational errors, it is entirely possible to have all three bearing lines intersect at a single point, but the radio fix may not at all correspond to the actual position of the radio transmitter. For this reason, a three bearing radio fix can never be classed as being reliable and even when the angle between the outside bearing lines approaches the favorable 90 degree cut such a radio fix can never be rated better than fair.

In order to obtain a good radio fix, it is practically necessary that at least four radio bearings be taken. It has been found that by taking a fourth bearing, or even more, that these will give confirmatory information which enables experienced personnel to judge whether the quality of the radio fix is good. By taking into account the angles between radio bearings, the distribution of the radio direction finders with respect to the probable radio fix, and the effect of propagation conditions on the accuracy of the radio bearings, remarkably good radio fixes are possible. The process of taking into account these factors is called "evaluation of bearings." However, for long range work more elaborate equipment is required due to the nature of radio propagation.

When a signal is emitted from a radio transmitting antenna, a portion of the total signal power leaves the antenna in all directions and travels parallel to the surface of the earth. In accordance with well-known physical laws the signal strength decreases as the distance between the transmitter and radio receiver and continues until the signal strength or intensity is too low to actuate the receiver. This is commonly known as the ground wave - the distance range of which does not generally exceed 100 miles except under certain favorable circumstances. Within the ground wave distance range the loop direction finder will function satisfactorily. The mobile units of the RID operate within this range when taking their short-range bearings.

Part of the total signal power is emitted from a radio transmitting antenna at various angles above the ground. This portion of the signal travels skyward until it reaches a region known as the Kennelly-Heaviside layer. This region consists of electrified particles created as a result of solar radiations striking the outer limits of the earth's atmosphere. In accordance with well-known physical laws, some signals are reflected and returned to earth where they are capable of actuating a radio receiver which may be thousands of miles from a radio transmitter. A signal arriving by this means is known as the skywave signal. In the process of signal reflection, an electrical change in signal occurs resulting in the production of two signal components one of which is said to be horizontally polarized and the other vertically polarized. The combination or resultant of these two components forms. the skywave signal. Inexperienced personnel, unable to distinguish between ground wave and skywave signals, frequently attempt to take radio bearings on skywave signals with loop-operated equipment with the result that the radio fix obtained by projecting such bearings is invariably in error.

Using an aerial of special design, it is possible to obtain the same directional characteristics as that possessed by a loop and the horizontally polarized error inherent in the loop is reduced to a negligible value. This type of signal collector, together with its associated receiver (Hallicrafters SX-28) is commonly called the Adcock direction finder. The dipoles, or collecting portions of the equipment consist of a rotating beam and balanced H antenna. Each of the vertical dipoles are approximately 20 feet long. The spacing between these vertical elements is also approximately 20 feet. These elements, resembling the letter H, are supported at their centers and interconnected by a horizontal transmission line from the midpoint of which signal energy is taken and delivered to the radio receiver. The beam is supported at its center on a small hut on top of a tower approximately 20 feet above the ground.

Unlike the ordinary radio receiver used for broadcast station reception, both the loop and Adcock type of direction finders must be located at sites carefully selected to minimize those effects which are capable of introducing errors in radio bearings. In general, such locations must be out in open flat country, free from electrical noise-producing industrial areas, free from overhead wiring, such as aerials, power, telephone and telegraph lines, free from barbed wire and other metallic fences, and free from wooded areas. In order to keep the site error low, separation from the direction finder to the obstructions mentioned must be not less than about 350 feet.

The basic reasons for providing good base lines for radio direction finders has already been discussed. From experience gained prior to Pearl Harbor, and that obtained in dealing with the many and varied problems since that date, the RID has evolved a direction finding network which has proven to be adequate in quickly locating the source of any radio signal. A network capable of rendering satisfactory service over the entire continental United States, its territories and possessions, is necessarily extensive because of the physical laws that govern radio propagation. For example, a radio transmitter located in New York City and operating on frequencies below 5 megacycles would have a distance range of only a few hundred miles during daytime hours. In order to obtain a sufficient number of radio bearings to obtain a good radio fix, it is obvious that a substantial number of direction finders would be necessary east of the Mississippi River. It is also obvious that direction finders west of the Mississippi would be worthless in the problem cited because of the inability to hear the signal of the station on which bearings are desired. For such reasons, the RID direction finder system is composed of several networks, each reporting to its regional clearing house of information called an Intelligence Center. Here the efforts of each direction finder are directed, coordinated and evaluated.

A major factor in the successful coordination of a direction finder network is communications. Of the hundreds of radio signals appearing in a small section of the radio frequency spectrum, the problem of directing the efforts of several direction finders to a specific signal to make certain that all bearings are taken simultaneously on the desired signal requires a thoroughly reliable communications circuit from each direction finder to its intelligence center. In the RID this is accomplished by using both radio and wire teletypewriter service, the former being used in the outlying territorial and secondary direction finders and the latter in the important primary stations.

In performing operations leading to the location of an illegal or clandestine transmitter, the direction finding nets are operated as one net and controlled from the Division's Headquarters in Washington. Intelligence Centers control regional nets for the purpose of rendering emergency direction finding service to aircraft, locating the sources of interference to radio services and for certain other operations.

It has been found that the accuracy of a bearing will vary with the time of day, atmospheric conditions along the route of propagation from the transmitter to the direction finder, and a variety of other factors. The accuracy of the fix, in turn, will depend on how well the bearings are evaluated. To cope with this problem, the RID has made extensive studies of the variation of bearings taken through the so-called "twilight zone" and other atmospheric peculiarities, and has charted the corrections to be applied to observed bearings to compensate for such conditions as twilight and distance. The RID furthermore has made a study of radio propagation factors, the effect of the sun spot cycle, etc., on long range direction finding.

It is a routine procedure for the RID personnel to take periodic "check bearings" on various known stations to determine any deviation in the accuracy of the bearings supplied by each direction finder. As a result, RID has developed a whole series of check-bearing procedures by which it can determine from day to day what deviations may be expected from particular direction finders on particular frequencies and at particular times.

There is an inevitable tendency for radio operators taking bearings on known stations to approximate these bearing readings to the bearings which they know in advance to be correct. The RID has developed its check-bearing procedures to such an extent that where an operator turns in a bearing on a known station which is more accurate than conditions warrant, his bearing can be questioned.

While direction finding is absolutely essential in the location of subversive or illegal transmitters, it has many other uses. For example, the same techniques are employed in tracking down the source of interference to licensed broadcast stations. Such interference may come from another station which is operating improperly or from some medical or industrial device using equipment which generates radio interference. One of the most important uses for radio direction finding techniques is fixing the position of lost aircraft. Bearings can be taken on a plane which does not know its position and the pilot can then be advised by radio of his position and the proper course to fly to bring him to his desired destination or to a safe landing.

The RID has standing requests from a number of government agencies which require it to intercept the traffic of thousands of foreign non-military stations. The simplest form for making an intercept is for the operator to listen to the transmission through headphones and simultaneously type the message. The maximum speed for this type of operation rarely exceeds 40 words per minute. Sometimes it is not feasible to transcribe the message simultaneously with its transmission and it is then necessary to make a Dictaphone cylinder or a flat disc recording.

Frequently, radio intelligence transmissions instead of being sent by manual keying are sent by mechanical devices at speeds up to 500 words per minute. These high speed transmissions cannot be transcribed manually. Accordingly, for this type of transmission a high speed tape recorder is employed. It is possible for operators without any skill in aural reception of radio signals to learn to accurately read such tape and transcribe it on a typewriter.

Another type of tape recording device is the Hellescreiber which, instead of printing dots and dashes, actually prints letters and words on the tape.

It should be pointed out that frequently single monitoring stations, because of the physical laws which govern long distance radio transmission, cannot obtain a full and complete copy or recording of the radio signal being intercepted. To remedy this it is necessary to have two or more monitoring stations intercept the same transmission. When, because of fading, the signal cannot be received intelligibly at one point, it is possible at that very same moment to receive it clearly at another point. By putting together the incomplete or "broken" copy received by several monitoring stations, it is possible for the RID to furnish the interested government agency with a "solid" copy of the foreign transmission.

The RID also records voice broadcasts and radiotelegraph press dispatches from foreign stations throughout the world for the Commission's Foreign Broadcast Intelligence Service. For this work, RID maintains five units which are known as Broadcast Recording Units. These units are in addition to the physical set-up previously described and they are located at Silver Hill, Maryland; Hato Rey. Puerto Rico; Kingsville, Texas; Hayward, California, and Portland, Oregon.

After V -day we expect to see an ever-increasing demand on the RID for the taking of bearings on lost aircraft piloted by private fliers. The Civil Aeronautics Administration expects a tremendous increase in air traffic. Even with new electronic devices, many of them automatic, there will, still be many planes lost and it will be the job of the RID to find them and to direct them to a safe landing. The finding of boats of many varieties will also make it necessary for the RID to expand its activities.

We point with pride to the fact that 70% of the total personnel of the RID are licensed radio amateurs - just another "case history" which should point out to the public that without these hobbyists America might still be faced with the problem of ridding the country of foreign spies - operating illegal transmitters and transmitting vital information to the enemy. Thanks to Radio Intelligence-such clandestine stations are now almost non-existent.

Posted March 18, 2021