Patented Apr. 28, 1953 RADIO AUDIENCE CUNTIN G SYSTEM neben Evan Shelby, `realiser, N. J., assignor tu Radio Corporation of America', a corporation ci' Delaware Application October 21, 1949, Serial No. 122,637
' v3 Claims'. 1 The inventionpertainsto radio and .television broadcasting and particularly to means and ap paratus for determining the number of receivimg sets tuned to a given broadcasting station in a given area at a given time.
f Successful operation ci a radio or televisionbroadcasting station from. a commercial stand-l point. requires that the operators have some knowledge. as to the` number of receiving sets which arereceiving. the intelligence broadcast by that station. in the past, this informationiias beengathered practicallyA entirely by human operators telephoning possible listeners selected at random from a local telephone directory. and interrogating the same.. This method, while extremely simple, is economically expensive. and, moreover, possesses many practical disadvantages, among which are the fact that telephone directory listing has no correlation to the radio set owners in a given area, that only relatively light sampling canbe effected for any one broadcasting day, and that it is necessary to disturb members of the listening audience, which. is considered highly undesirable. Furthermore, withV this method it is next to impossible to determine whether thelistener under consideration is listening to an entire program` or only to a portion thereof.
Accordingly, it is an object of the invention toprovide means and. apparatus for automati cally determining the approximate number of radio or television sets tuned to a given broadcasting station in agiven area at a given time.
It is another object of the invention to provide means and apparatus for determining the extent of the listening audience oi a local broad oasting station without disturbing thataudience.
A further object of the invention is to provide meansand apparatus for computing the approximate number of radio receivers tuned to a given broadcasting stationwhich does not require addi-v tional apparatus at the receiver..
Still another object of the inventionis to provide means and apparatus tosimultaneously determine whether. or not a large number of receiving sets in a given area are tuned tothe broad.- casting station under consideration.
It is a still further object of the invention to provide means and apparatus for. determiningthe' extent of the listening audience of a radio station Without interrupting the program transmitted or disturbing the audience in any Way. It is anadditional object of the invention to providemeans to determine the total number of receivingsets tuned to a given broadcasting station at-*shorttime-intervals; -v
attained according to the invention by utilizing.
the underlying principle that a large percentage of all broadcast receivers have some form of automatic gain control. When such a receiver is tuned to a strong carrier, the A. G. C. operates to lower the anode current in certain tubes in the receiver and thereby reduces slightly the power drawn from the primary power supply by the receiver. Now, it is recognized, of course, that this feature is not found in all radio receivers in a given service area since some would not be equipped with A. G. C., some would be battery-operated, etc. But nevertheless, a very worthwhile sample of total audience may be tapped by the proposed method. According to the invention, the carrier of the broadcast station is turned oil entirely or the strength of the carrier is commen'surably reduced for a short interval of time and the variation in total power supplied by the central power station is simultaneously measured. Should the broadcast transmitter derive its primary power from the same source as the receivers, it is of course necessary to apply a correction to the measurement to compensate for the power decrease occasioned by the interruption of the carrier wave. The length of the interval during which the carrier is turned ofi or changed in amplitude is necessarily determined by the time constant of the power supply network serving the area in question. It is contemplated that only a fraction of a second would be necessary, but it is recognized that in some instances it might have to be one or more seconds. This test operation is naturally carried out during a suitable lull in the program being transmitted, though if the time interval required for the test is suciently short, it will be unnoticed by most listeners. Measurement of the power increment or decrement at the central power station must be synchronized with the change in the broadcast carrier strength and this is done by suitable wire line connection or by radio monitoring of the carrier at the power station.
The invention will be described in detail with reference to the accompanying drawing forming a part of the specicaticn and in which the solegure illustrates apparatus for determining the approximate number of radioreceivers tuned paratus I3, connected to a primary power distribution bus I5, in turn connected to secondary distribution busses Il and I9 for the distributionl of electric power throughout the service area supplied by the local power company. The usual power load, illustrated by blocks 2|, and a number of radio and television receiving sets 23-26 will be operatively connected to secondary busses il` and i9. These will be found to be of four classes: voice modulated receivers with automatic gain control, 23; Voice modulated receivers without lautomatic gain control, the latter of which receivers are gradually being replaced by the former, 24; television receivers with automatic gainv control, 25; and television receivers without automatic gain control, 26. The voice modulation receivers may be either amplitude modulation or frequency modulation receivers, of which approximately 90 per cent or greater will incorporate automatic gain control and it is considered that 95 per cent or more of the television receivers will incorporate automatic gain control features. Within the above mentioned electric power service area there will be located a voice modulated broadcast station 3l and perhaps a television broadcast station 33, to which one or more receivers 23-25 may be tuned and the determination of at least the approximate numbers of which for each type of broadcast is desired.
According to the invention, sensitive power measuring devices 35, 36 are interposed in the electric distribution system between the power generating apparatus H and the loads, represented by non-receiver power loads 2l and the loads imposed by receivers 23-25, and arranged to measure the power consumed by the loads on secondary distribution busses I1 and I9. These power measuring devices are contemplated to be operated in conjunction with existingpower measuring circuitry employed by the local power company and must meet certain special requirements detailed below. In the simplest arrangement according to the invention, the carrier wave produced by transmitter 4I which is modulated either in amplitude or frequency with a program obtained from a program source 43 preferably is substantially suppressed, or entirely interrupted, for a short time interval in response to operation of control circuitry 45 which also upon initiating operation to control the carrier strength actuates power measuring device 35 over wireline yconnection 41 to determine a power reference v level whereupon the changes in carrier strength will affect those receivers tuned to transmitter 4I and incorporating A. G. C. features to increase power consumption, which increase will be reflected by power measuring device 35 and transmitted via wire line 49 to a data indicator 5|. Data indicator l may be of any known telemetering indicator device, numerous examples of which may be had by reference to the book Principles and Methods of Telemetering by Borden and rIhynell, Reinhold- Publishing Company, 1948,
Control circuitry 45 may comprise known electronic circuits, preferably pushbutton actuated, comprising a relaying circuit to actuate power measuring device 35 to obtain a reference indication of the power consumption immediately prior to change in carrier intensity, a relaying circuit to eiect the change in carrier intenstiy, and timing circuits to control the relaying circuitry in proper sequence. As an example of such control circuitry in the simplest form, a push-button switch may be used to operate a relay at transmitter 4| the contacts of which are arranged to vary the intensity of the carrier wave in known manner, such as varying the bias on a buier amplifier for example, and at the same time operate a relay at power measuring device 35 the contacts of which are arranged to connect operating power to the recording apparatus. The relay at transmitter 4| should be somewhat slow to act in order that the power level be measured just prior to change in carrier wave intensity and the relay at device 35 should be slow to release so that the power levels prior to and after carrier intensity change both are indicated. As alternate embodiments, electronic relay circuitry such as multivibrators or transient responsive circuitry such as dierentiating and integrating circuits may be employed accordingto established prac- ,y
adopted for this purpose by those skilled in the art, for example, a balanced bridge arrangement may be used, in which case the bridge is preferably balanced by motor driven means in response to control circuitry 45 just prior to the change in carrier intensity. An oscilloscope may be employed to indicate power increment, but preferably some known form of data transmission circuitry, such as a frequency shift telemetering system commonly used by power and utility companies, would be employed.
Any known form of data indicator 5I may be used, the counter type being considered most convenient. If the latter is used, it may be reset to zero prior to the indication operation by control circuitry 45 as indicated schematically by connection 53. In its simplest form, an ordinary resetting counter mechanism is arranged to have the count bar actuated by thel data transmission circuitry. For example, with a telemetering system transmitting intelligence in the form of a number of cycles of a constant frequency wave or a number of pulses proportional to the amount of change in power consumed, a multivibrator circuit may be triggered and a solenoid in the output circuit thereof may be arranged to actuate the count bar of the mechanism. Similarly, contacts of the push button or one of the relays actuated thereby may be arranged to energize another solenoid, or a stepping type relay; the armature of which is coupled to the reset bar of the counter mechanism to set the counter to zero at the beginning.
Since the various receivers in the area being surveyed will beat different distances from the broadcast transmitter and will receive signals of varying strength for `that and other reasons and also because various makes and types of receivers will have different characteristics in this regard, and the fact that there will background only.
.bescmezrecevers not lprovided with A. G. C. and
some battery operated receivers inuse -should be considered, lit is not considered feasible to calculate the exact number of receivers directly from the change in power load at the power station. It is lbelieved preferable to obtain data as outlined above and correlate the results with studies Ymade simultaneously by other accepted methods of audience measurement. Even without 'such correlation, however, this method ,provides any excellent means of comparing audience size for different programs. In an area vsuch as metropolitan New York, which is'served by several different power supply sources, it would be feasible to make the measurements simultaneously in two or more power stations. Furthermore, it is contemplated that under some circumstances it may be desirable to practice the invention in rather small divisions or a `power network, such as a housing development or even a single apartment dwelling. More vreliable results 'may be obtainedby having several such measurements at suitable intervals and taking an'average of the change in total power, in order to average out effects due to changes in total power caused by equipment other than radio receivers.
It is also contemplated according to the inventio'n to determine the approximate number of television receivers tuned to a given television broadcast station by modifying the arrangement A hereinbefore described to the extent that control circuitry 65, which may be of substantially the same construction as control circuitry 45, Will cause a television transmitter 6| to transmit a black level signal for the prescribed measuring interval immediately following or preceding a white level signal, as a result of which power measuring devices 35 and 36 will provide an indication of the power increment clue to the change in power drawn by the picture tube of television receiver 25. As employed herein, the term black level signal refers to that extreme value of signal which would be transmitted under normal conditions if the picture consisted of a black background only and the term white level signal refers to that signal which would be transmitted if the picture consisted of a white It is considered within the scope of those skilled in the art to arrange control circuitry 65 either to actuate transmitter 6I to transmit a black level signal after a white level signal has been transmitted in response to a television program source 63 or to interpose a white level signal followed by a black level signal, or vice versa, whichever is desired.
It is obvious from the foregoing description that no interference will arise between determinations made by two or more V. M. or T. V. broadcasting stations operating in the same service area provided the determinations are not made at the same time. In order to assure that the latter condition will not be disregarded, it is considered preferable that some measure be taken to prevent overlapping use of the common facilities. In the simplest arrangement conceivable, where television and voice modulation transmitters are located in the same building, as may become common practice, a simple wire line interlock circuit, indicated by connection 61 is provided, for example, a simple back and front contact interconnection having in circuit therewith a slow-acting relay or other time delay circuit rendering the engagement of control circuitry 65 initiating means inoperative for a pre- 6 ldetermined period after kthe actuation of 'the means vinitiating operation of control circuitry 45. In other installations the wire line may be replaced .by more complex but readily available means mentioned in greater detail below.
While connections 6l, 49, and 6l have been described as wire line connections in order to illustrate a basic arrangement of the invention, it is within the scope of the invention to utilize carrier `current communications systems currently employed by utility companies with equally efficient results. Under some circum-` stances the use of such expedients will not be available and resort may then be made Lto other telemetering schemes, examples or" some of which that are obviously applicable to the basic invention will be found in the book, Principles and Methods of Telemetering by P. A. Borden and G. M. Thynell, published by Reinhold Publishing Corp., 1948. In such a case, it is contemplated that the operation be carried out by modifying a conventional receiver in accordance with known circuitry to provide a control receiver 'll located .near power measuring device 35 and tuned to transmitter 4| to actuate the former in response to carrier intensity changes. Power measuring device 35, under control receiverv 1I andcontrol circuitry 45 would provide an output indicative of the desired intelligence which is then used to modulate a data transmitter 13 to 'elay the data to a data receiver 'l5 by means of a radiant energy beam path established by U. H. F. antennas 'I1 and '19. l
Alternatively a completely separate communication system is provided as shown by control transmitter and data receiver 8i operable under control vofcontrol circuitry to transmit conditioning signals to a control receiver and data transmitter 83 over a radio relaying path established by antennas 8l and 8S. Receiver-transmitter 83 is operatively coupled to power measuring device 36 as in the previously mentioned arrangement for control of device 36 and transmission of the resultant data back to data indicator 9| which may be of substantially the same construction as data indicator 5| although it is not necessarily so limited. An advantage of this more complex arrangement is of course found in its use as an auxiliary communication channel between the power measuring point and the broadcasting station.
While the invention has been described in terms of rather specific embodiments, it should be understood that other arrangements will be suggested to one skilled in the art without departing from the spirit and scope of the invention.
1. An arrangement for obtaining an indication of the number of radio receivers tuned to a transmitter broadcasting a carrier wave, comprising a common electric power distribution system, a plurality of radio wave receivers drawing operating power from said common electric power distribution system, said receivers having automatic control of gain and thereby respending in the normal mode of reception of an intelligence carrying continuous carrier wave to a change in characteristics of the received carrier wave with a change in power drawn from said common electric power distribution system, a power measuring device coupled to said common electric distribution system to measure the power flowing therein, and means substantially and abnormally to alter the amplitude of said given intelligence carrying continuouscarrie'r wave to cause the amount of power drawn by said radio .wave receivers from saidxcommon electric distributioncircuit to vary, the variation in said power drawn at the time of said alteration being a measure of the number of radio wave receivers receiving said given carrier wave.
2. An arrangement for obtaining an indication of the number of radio receiversxtuned to a transmitterv broadcasting a carrier wave of given characteristics, comprising a common electric power distribution system, a plurality of radio wave receivers drawing operating power from said common electric power distribution system, said receivers incorporating automatic gain control circuits responding in the normal mode of reception of an intelligence carrying continuous carrier wave to a change in signal strength of the received carrier wave with a change in power drawn from said common electric power distribution system, a power measuring device coupled to said common electric distribution system to'measure the power owing therein, and means to suppress said given intelligence carrying continuous carrier wave to cause the amount of power drawn by said radio wave receivers from said common electric distribution circuit to increase, thewincrease in power drawn during the time of alteration being a measure of the number of radio wave receivers receiving said given carrier wave.
3. An arrangement for obtaining an indication of the number of television receivers tuned to a transmitter broadcasting a carrier wave modulated by picture signals, comprising a common electric power distribution system, a plurality of' television f program receivers .drawingpper ating power from said commonvelectricpower ldistribution system, said receivers beingof the type responding in the normal mode of reception of a visual program modulated continuous carrier wave to a change in level of the picture signal modulation of the received modulated continuous carrier wave with a change in power drawn from said common electric power dis-l tribution system, a power measuring device coupled to said common electric distribution system to measure the power owing therein, and means to vary the picture signal level of said visual carrier wave to one of the limits of said modulation to cause the amount of power drawn by said television receivers from said common electric distribution circuit to vary to the ex`- treme amount possible, the variation in said power drawn at the time of said variation being a measure of the number of television receivers receiving said visual carrier wave.
ROBERT EVART SHELBY.
References cited in the sie of this patent;
UNITED STATES PATENTS Date OTHER REFERENCES y Tele-Tech; pages 38, 39, 64, 65; May 1949.V