WO1995023980A2

WO1995023980A2 - Method and equipment for conducting a survey among the listeners of radio stations

Info

Publication number: WO1995023980A2
Application number: PCT/FI1995/000104
Authority: WO
Inventors: Jorma KIVELÄ
Original assignee: Jutel Oy
Priority date: 1994-02-28
Filing date: 1995-02-27
Publication date: 1995-09-08
Also published as: FI940942A0; WO1995023980A3; FI940942L; FI98022B; FI98022C

Abstract

The present invention relates to a method and equipment for conducting a survey among the listeners of radio stations. The method comprises measuring the total amounts of listeners of radio stations by observing the leakage radiation signals of the local oscillators of the radio receivers of the vehicles passing the measuring point, this observation being carried out essentially simultaneously at several predetermined frequencies, which are dependent on the frequencies of the radio stations that one wants to observe. In the calculation of the numbers of listeners, the measurement result of the number of listeners of each radio station is increased when the frequency of the leakage radiation signal of the local oscillator of the radio receiver of a vehicle passing the measuring point includes the information that the radio receiver of said vehicle was tuned into the frequency of said radio station.

Description

Method and equipment for conducting a survey among the listeners of radio stations

The present invention relates to a method for conducting a survey among the listeners of radio stations.

The invention also relates to equipment for conducting a survey among the listeners of radio stations, this equipment comprising a radio receiver unit and an antenna means connected thereto.

The present invention relates to conducting surveys among the listeners of public radio stations, especially commercial and broadcasting radio stations. Conducting surveys among listeners is a method by which radio stations can examine the popularity of a radio station. Listener surveys are a way to measure the popularity of a radio station, the results of these surveys being a means by which radio stations can improve their competitiveness. The most important thing for radio stations in pursuit of numbers of listeners is to improve the broadcast program such that it will become as popular as possible among listeners. This is particularly important to commercial radio stations, the operation of which is based on selling advertising time included in the program directed at the listeners.

Listener surveys are conducted by both radio stations themselves and companies specialized in conducting listener surveys. Traditionally, the listener surveys of radio stations have been conducted by means of interviews. These types of methods are, however, very difficult. o carry out, require human resources, entail great expenses, and are also unreliable as to their results, because the interview situation occurs rarely at the same time as a radio station is being listened to. Because of the above-mentioned reasons, listener surveys are conducted relatively seldom. Due to the above-mentioned reasons, using results derived with interviewing methods to improve the program of a radio station is some kind of "shooting in the dark", because direct detailed information on the effects of different factors on the popularity among listeners is difficult to obtain from these results.

Technical auxiliary means and methods have also been developed for examining the numbers of listeners. In one of these methods, a statistically sufficiently large group of test persons, for instance 2,000 test persons, have been given listening apparatuses, which register sign signals hidden in the transmission signals of radio stations. Naturally, the sign signals of different radio stations are different in order that conducting the listening survey may be possible. The results registered by the listening apparatuses are later fed into a common data processing apparatus, which calculates the amounts and proportions of listeners of the different stations. By means of this type of method, better and more reliable results are achieved than with interviewing methods. The method is however artificial in some way, because a special listening apparatus has been given to be carried by predetermined test persons. Artificiality is added to by the fact that the person using a listening apparatus knows that the switch to another station that he performs is noticed, and this may have an effect on how readily a person switches to another radio station after all. The method requires a great amount, for instance 2,000, active test persons and as many listening apparatuses, and in addition to that, also changes in the equipment of the radio stations in order that it would be possible to connect sign signals to the transmission signal. The method also requires a great amount of work and operations for delivering the listening apparatuses to the place where the data is collected, and also plenty of work for breaking down the data from the 2,000 listening apparatuses. The object of the present invention is to provide a new type of method for conducting a survey among the listeners of radio stations, by which method the problems associated with the known solutions are avoided. This object is achieved with the method of the invention, characterized in that the method comprises measuring the total amounts of listeners of radio stations by observing the leakage radiation signals of the local oscillators of the radio receivers of the vehicles passing the measuring point, this observation being carried out essentially simultaneously at several predetermined frequencies, which are dependent on the frequencies of the radio stations that one wants to observe, and that in the calculation of the numbers of listeners, the measurement result of the number of listeners of each radio station is increased when the leakage radiation signal of the local oscillator of the radio receiver of a vehicle passing the measuring point includes the information that the radio receiver of said vehicle was tuned in to the frequency of said radio station.

The equipment of the invention is characterized in that the equipment or at least the antenna means thereof is located in the vicinity of the roadway along which vehicles move; that the equipment comprises means for obserying the leakage radiation signals of the local oscillators of the radio receivers of the vehicles passing the antenna means, this observation being carried out essentially simultaneously at several predetermined frequencies, which are dependent on the frequencies of the radio stations that one wants to observe; and that the equipment further comprises calculating means connected to a radio receiver unit for increasing the measurement result of the total amount of listeners of each radio s.tation when the frequency of the leakage radiation signal of a local oscillator received by the radio receiver unit includes the information that said radio station is being listened to in the vehicle. The invention is based on the technical basic structure of the observed radio receivers. In practice, each radio receiver functions on a so-called super receiver principle. In this type of radio receiver, each radio station that is listened to has a corresponding local oscillator signal frequency, which is constant for the commonly used receivers. In general, this local oscillator signal frequency is the frequency of the radio station listened to by the radio receiver added by an intermediate frequency, which is generally 10.7 MHz. This local oscillator signal leaks slightly also outside the receiver through the antenna of the radio receiver. According to the applicant's observations, the field strength of the leakage radiation of a local oscillator is still sufficiently great in order to be observed even at a distance of over ten metres from the vehicle.

Monitoring the leakage radiation signal of the local oscillator of a radio receiver is known as such for instance in monitoring illegal police radio receivers. In this application, it is not a question of conducting a survey among listeners in which monitoring and observation of the total amounts of listeners of several public radio stations would be carried out. The methods and equipment used in the above-mentioned application are not suitable for conducting surveys among the listeners of radio stations.

The basic idea of the present invention is to utilize in a new manner an existing phenomenon known as such, i.e. the leakage radiation of the local oscillator of a radio receiver, in such a manner that a classification of the numbers of the listeners of radio stations is provided by calculating and classifying the received leakage radiation signals. The object of the invention is to monitor listening to the radio carried out by the passing car traffic. The object is to find out what is the mutual market share of listeners among different radio stations. By means of the method, it is possible to discover how many vehicles listening to each radio station are observed to drive past the equipment within a certain time unit.

Many advantages are achieved with the method of the invention. The method is passive as regards the listener of a radio station and thus requires no measures on the part of the listener, and therefore the results are absolutely objective. A listener situated in a vehicle does not even notice that he has been observed as to what radio station was listened to in the vehicle. The invention utilizes the existing traffic, i.e. the normal movement of vehicles on a roadway, whereby measurement results are produced automatically when a vehicle passes the measuring point. The measurement results are also stored automatically at the same time, no separate laborious measures being thus needed for breaking down the measurement results. The method and equipment are practicable also in the sense that their use does not require the transmission signals of radio stations to be provided with any sign signals. With the method, a large measurement group can be obtained easily and quickly, which improves the reliability of the results statistically. For example, it is possible for 2,000 vehicles, for instance, in which a radio station is being listened to, to pass within a short time even through road sections which are not particularly busy. In the invention, a survey among listeners is conducted by means of the radio receivers of vehicles. With regard to the improvement of the program of a radio station, a vehicle, which is in practice a car, is the best possible place to conduct a survey among listeners, because it is in a car that a listener switches to another channel most easily and quickly if the program is not to his liking. The method and equipment of the invention offer reliable real-time information which corresponds to a real situation. The method and equipment of the invention provide a solution for acquiring the feedback needed for the development work of the program profile of a radio station, this solution being easy, reliable, quick and easy to repeat. Due to the real-time factor, the information can be used together with the "run list" of the programs to improve the program profile of a radio station in such a manner that the popularity among the listeners of the station can be improved. Correspondingly, it is possible to examine changes in the popularity of competing radio stations and the correlation of these changes with programs. Listener feedback measured from a moving vehicle, in the production of which feedback a listener takes no active role, is the most direct and reliable feedback, which also includes information on how a listener reacts to the internal structure of a program. By comparing for instance programs determined for different times of a day with simultaneous data on the proportion of listeners, the popularity of a station can be maximized, because the different factors affecting the popularity can be discovered. Changes in the numbers of listeners and the directions of these changes can be noticed immediately. In addition to the popularity of a certain station, the situation of competitors can also be seen immediately, and this can also be utilized. The method and equipment of the invention are primarily suitable for improving the programs of radio stations and for supporting the planning and implementation of advertisement selling.

In the following, the invention will be described in more detail with reference to the accompanying drawings, in which

Figure 1 shows a first embodiment of the invention,

Figure 2 shows a second embodiment of the invention,

Figure 3 shows a third embodiment of the invention,

Figure 4 shows a block diagram of the radio receiver unit of the equipment of the invention, Figure 5 shows a block diagram of a normal super-type FM radio receiver,

Figure 6 shows the location of the equipment of the invention in a tunnel,

Figure 7 shows an envelope formed by the leakage radiation of a local oscillator signal passing a measuring point,

Figure 8 shows the common envelope of the leakage radiation of a local oscillator signal passing a measuring point and the radio transmission interfering in the background,

Figure 9 shows a sum signal received by several antenna means.

With reference to Figure 5 at first, a block diagram of a normal super receiver A of the FM range is shown. The block diagram of radio receivers A provided in vehicles is similar to Figure 5. The radio receiver comprises a pre-stage consisting of an amplifier la and a filter lb, a local oscillator 2, a mixer 3, an ^' intermediate frequency filter 4, a detector 5, and an antenna 6. The pre-stage consists of an amplifier la and a filter lb dimensioned for a desired frequency range (FM frequency range 87.5 - 108 MHz). The signal of the local oscillator 2 is mixed in the mixer 3 with a radio- frequency signal arriving from the antenna 6 via the pre-stage la, lb, the result being an intermediate frequency signal, which is filtered so as to be separate with the intermediate frequency filter 4. The frequency F(loc) of the local oscillator 2 is the frequency of the station that is being listened to added by 10.7 MHz. The frequency 10.7 MHz is a so-called intermediate frequency, which is generally used. The intermediate frequency signal is applied to the detector 5, after which a desired audio-frequency output signal 7 is obtained. The signal of the local oscillator 2 leaks slightly backwards in the receiver through the pre-stage la, lb primarily via the antenna 6. This leakage can be observed as a weak fixed-frequency radio transmission 10.7 MHz above the listening frequency. This signal can normally be measured even at a distance of over 10 metres. In Figures 1, 3 and 5, leakage radiation is indicated by a sign B.

It is possible to detect the leakage radiation B of the local oscillators from among possible disturbance signals, because it has a fixed frequency, and its signal form is such that the field strength of the signal rises quickly and falls equally quickly unlike disturbance signals do.

With reference to Figures 1 - 3, vehicles 11- 13 move along a roadway 10. Each vehicle comprises a radio receiver A of the type shown in Figure 5, the local oscillators 2 of this radio receiver radiating leakage radiation B through the antennas lla-13a of the radio receivers of the vehicles 11-13. The antennas 11a- 13a correspond to the antenna 6 in Figure 5. Measuring equipment 14 is located in the vicinity of the roadway 10, this measuring equipment comprising a radio receiver unit 15, an antenna means 16, and a cable 17 between the radio receiver unit 15 and the antenna means 16. The purpose of the radio receiver unit 15 is to observe the leakage radiation signals B of the local oscillators 2, these signals being received by the antenna means 16 from the antennas 11a-13a of the radio receivers of the vehicles 11-13. Furthermore, calculating means 18 can be noticed in Figures 1-3, these means being connected to the radio receiver unit 15 by a cable 19. The calculating means 18 are most preferably provided by means of a microcomputer. The purpose of the calculating means 18, such as a microcomputer, is to calculate, i.e. to register, pulses arriving from the radio receiver unit 15, these pulses being dependent on the frequency of the local oscillator leakage signal B received by the antenna means 16 from the radio receiver A of a passing vehicle to the radio receiver unit 15 of the equipment. Apart from functioning as a calculating means, the microcomputer 18 also acts as a means for storing the pulses arriving from the radio receiver unit 15. In all of the Figures 1-3, the equipment also comprises a message terminal 20, which can also be implemented by the same microcomputer. Assume next that in the locality and more specifically, the measuring point, in question, it is possible to listen to three radio stations, i.e. radio stations Rl, R2 and R3. Assume that the transmit frequency of the radio station Rl is 90 MHz, the transmit frequency of the radio station R2 is 95 MHz, and the transmit frequency of the radio station R3 is 100 MHz. The intermediate frequency of radio receivers is normally 10.7 MHz, which means that if the radio station Rl is listened to with the radio receiver A of the vehicle 11, for instance, the frequency of the local oscillator 2 of the radio receiver A of the vehicle 11 is 100.7 MHz, which is thus also the frequency of the leakage radiation B of the local oscillator 2. If the radio station R2 is listened to with the radio receiver A of the vehicle 11, the frequency of the local oscillator 2 of the radio receiver A of the vehicle 11 is 105.7 MHz, which is thus also the frequency of the leakage radiation B of the local oscillator 2. If the radio station R3 is listened to with the radio receiver A of the vehicle 11, the frequency of the local oscillator 2 of the radio receiver A of the vehicle 11 is 110.7 MHz, which is thus also the frequency of the leakage radiation B of the local oscillator 2.

In the method of the invention, total numbers of listeners (total numbers of vehicles in which the station in question is being listened to) of the radio stations Rl, R2 and R3 are measured by observing the leakage radiation signals B of the local oscillators 2 of the radio receivers A of the vehicles passing the measuring point, these vehicles being for instance the vehicles 11-13. This observation is carried out by the antenna means 16 and the radio receiver unit 15, and the observation occurs essentially simultaneously at several predetermined frequencies such as frequencies 100.7 MHz, 105.7 MHz and 110.7 MHz, which are dependent on the frequencies 90 MHz, 95 MHz and 100 MHz of the radio stations Rl, R2 and R3 which one wants to observe. Dependency thus means that the leakage radiation signals B of the local oscillators 2 of the radio receivers A of the vehicles 11-13, these signals being received by the radio receiver unit 15 of the equipment, are higher by an intermediate frequency 10.7 MHz than the transmit frequencies of the radio stations received by the radio receivers of the vehicles. In the calculation of the number of listeners, the measurement result of the number of listeners of each radio station Rl, R2 and R3 is increased when the frequency of the leakage radiation signal B of the local oscillator 2 of the radio receiver A of the vehicle 11- 13 passing the measuring point, this frequency being received by the radio receiver unit 15, includes the information that the radio receiver A of said vehicle was tuned in to the frequency of said radio station Rl, R2, R3. If the radio receiver unit 15 receives leakage radiation B of the frequency of 100,7 MHz from the local oscillator of the radio receiver of the vehicle, the measurement result of the total number of listeners of the radio station Rl is increased in the measurement. If the radio receiver unit 15 receives leakage radiation B of the frequency of 105,7 MHz from the local oscillator of the radio receiver of the vehicle, the measurement result of the total number of listeners of the radio station R2 is increased in the measurement. If the radio receiver unit 15 receives leakage radiation B of the frequency of 110,7 MHz from the local oscillator of the radio receiver of the vehicle, the measurement result of the total number of listeners of the radio station R3 is increased in the measurement. To be exact, the total number of listeners does not refer in this context so much to the number of people who are listening to a certain radio station as to the number of vehicles which have passed the measuring point and in which a certain radio station is being listened to. Increasing the measurement result of the number of listeners is carried out in such a manner that the radio receiver unit 15 gives a pulse to the calculating means 18, i.e. for instance a microcomputer, in which the pulse increases the numerical value of the memory location corresponding to the observed radio station. In the preferred embodiment, the method comprises acting in such a manner that the proportions of listeners of several radio stations Rl, R2, R3 are determined on the basis of the measurement and calculation of the local oscillator signals B, which are dependent on the frequency of the radio station Rl, R2, R3 which is being listened to in a vehicle. Furthermore, the preferred embodiment comprises acting in such a manner that the information on the numbers and/or proportions of listeners, this information being measured by means of the method, is transferred to at least one of those radio stations Rl, R2, R3 the numbers of listeners of which are being measured. With reference to Figure 2, the equipment comprises a data processing apparatus 21 located for instance at the radio station, which apparatus can be for instance a microcomputer. Furthermore, the equipment comprises a data link 22 between the measuring point and the radio station, and modems 23 for transferring measurement data to the radio station. The measured data can be processed at the radio station for instance by means of ordinary statistical software by the microcomputer 21, whereby they are rendered in an illustrative form. The illustration of the information is represented by diagrams 24-26 in Figure 2. The circle diagram 24 represents the relative distribution of the listeners of the three radio stations Rl, R2, R3. The diagram 25 represents the numbers of listeners of the three radio stations Rl, R2, R3 as a function of time. The diagram 26 represents the numbers of listeners of one radio station Rl as a function of time. The measurement data can also be transferred somewhere else than a radio station, for instance to a company producing listener survey services, but at some stage, the measurement information most preferably finally ends up also at the radio stations in one way or another, because they get the most benefit from the information.

The information on which radio station the radio receiver of a vehicle was tuned in to is stored most preferably as a time-dependent signal, which was noticed in the diagrams 25 and 26, because this allows the time behaviour of the numbers and proportions of listeners to be followed.

In a preferred embodiment, a survey among the listeners of radio stations is conducted in a frequency band consisting of one or more units, this frequency band being entirely or partly comprehensive, and the lowest frequency of said frequency band being at least as low as the frequency of the radio station which has the lowest frequency added by the intermediate frequency of the local oscillator of a radio receiver, and the highest frequency of said frequency band being at least as high as the frequency of the radio station which has the highest frequency added by the intermediate frequency of the local oscillator of a radio receiver. In the case of the radio stations Rl, R2, R3, the lowest frequency would be at least as low as the frequency 100.7 MHz, and the highest frequency would be at least as high as the frequency 110.7 MHz.

In the preferred embodiment of the method, the radio receiver unit 15 receives leakage signals of the local oscillators of the radio receivers of vehicles on narrow bandwidths around the frequencies of the local oscillator signals, i.e. in the vicinity of the frequencies 100.7 MHz, 105.7 MHz and 110.7 MHz. In this manner, probabilities of error are reduced. Several (two) antenna means 16 and an adder means 27 are provided in the embodiment of Figure 3. In the preferred embodiment, the leakage radiation signals B of the local oscillator 2 of the radio receiver A of a vehicle are observed with several antenna means 16. A common mode signal S is produced from the signals received by the antenna means 16, and when this common mode signal is detected, the measurement result of the number of listeners of a radio station is increased. The common mode signal is represented in Figure 9. The use of several antenna means 16 reduces the probability that some disturbance signal could be interpreted by mistake as the leakage signal of a local oscillator. The common mode signal S is such a special signal that the occurrence of such a disturbance signal is extremely unlikely. An interference 200 due to propagation delays can be noticed in the common mode signal S, the existence of this interference contributing to accurate observation. Figure 6 shows the location of the equipment

15,16 of the invention in a tunnel 28. In the preferred embodiment, observation is carried out in the tunnel 28 which comprises a route along which vehicles 11 move, this tunnel being for instance an underpass or passage tunnel or similar relatively disturbance-free environment, because the probabilities of error are thus further reduced.

In Figure 2, the equipment also comprises a sensor means 29 such as an induction loop for observing whether there is a vehicle in the measuring area. The method thus comprises observing by means of the sensor means 29 whether there is a vehicle in the measuring area in addition to observing leakage signals by means of the radio receiver unit 15, and the measurement result of the number of listeners of a radio station is only increased when it is also noticed that there is a vehicle in the measuring area. This is another way of eliminating sources of error. The sensor means 29 embedded in the road is connected to the radio receiver 5 unit 15 by a cable 29a.

The message terminal 20 is shown in Figures 1- 3. The preferred embodiment of the method also comprises acting in such a manner that a special observation person working at the special message terminal 20 stores

10 additional information relating to the vehicle which is located at the measuring point and/or persons located in this vehicle, and that this additional information is connected with the information on the frequency of which station '•^' 1 , R2, R3 the radio receiver A of the

1.T vehicle was tuned in to. There is thus a person at the measuring point who provides additional observations for instance from the keyboard 20 of the microcomputer 18, these observations relating for instance to whether there was a man or a woman in the vehicle, whether the

20 person was young or old, and whether the vehicle was cheap or expensive.

In Figure 2, the equipment also preferably comprises a camera means 30, which is connected to the radio receiver unit 15 via a cable 31. In the preferred

25 embodiment, the method also comprises recording vehicles that pass the measuring point with the camera means. The pictorial record created in this way is connected with the information on what radio station the radio receiver of the vehicle was tuned in to. This enables storing

30 information on what radio station was listened to in the vehicle and information on what the car was like, and what type of persons were located in it, in such a manner that all this information is connected to each other. Furthermore, with reference to Figure 2, in the preferred embodiment, the equipment comprises an information display means 32, which is connected to the radio receiver unit 15 by a cable 33. In the preferred embodiment, the observation of the leakage radiation signal of the local oscillator of the radio receiver of a vehicle by means of the radio receiver unit 15 is used for activating the information display means 32 such as a billboard or similar information display means. If the radio receiver unit 15 detects for instance the frequency 100.7 MHz, in which case it is a question of the radio station Rl operating at the frequency 90 MHz, the advertising message could be for instance the thanks from the radio station to the driver for listening to that station. If some other station were listened to in the vehicle, like the station R2 or R3, the billboard 32 would request to switch to the frequency of the radio station Rl. This solution gives additional value to the invention. If there should be a desire to apply the invention for activating the information display means 32 in particular, the calculating means 18 would not necessarily be needed in that case, and the observation of only one leakage radiation frequency at the minimum would necessarily be required. In a preferred embodiment, signals that are essentially symmetrical as to their amplitude peaks are mainly observed in the method in order to eliminate disturbance signals. This is done for the reason that the leakage signal B of the local oscillator 2 that passes the measuring point by a linear propagating movement as a vehicle moves is of such a form. The radio receiver 15 can be designed in such a manner that it only reacts to signals that are of the form described above, i.e. to signals that rise and fall around their amplitude peaks. The envelopes shown in Figures 7 and 8 are signals of the form described above.

The radio receiver unit 15 is a device that observes several local oscillator frequencies to be followed, i.e. the frequencies 100.7 MHz, 105.7 MHz and 110.7 MHz in this case, these frequencies thus corresponding to the transmit frequencies of the radio stations Rl, R2, R3 added by an intermediate frequency 10.7 MHz. The observation of the leakage radiation B of the local oscillators 2, i.e. the observation of local oscillator signals can be implemented by either one receiver, which switches quickly from a channel to another, i.e. a so-called scanner, or several parallel receivers according to Figure 4. Figure 4 shows the block diagram of the radio receiver unit 15 which is able to observe three different stations Rl, R2, R3. The radio receiver unit 15 of the Figure 4 comprises three parallel receivers 151, 152 and 153. The first receiver section 151 of the radio receiver unit 15 is implemented in such a manner that it observes the frequency 100.7 MHz, which in practice means the observation of the listening to the radio station Rl in a vehicle. The second receiver section 152 of the radio receiver unit 15 is implemented in such a manner that it observes the frequency 105.7 MHz, which in practice means the observation of the listening to the radio station R2 in a vehicle. The third receiver section 153 of the radio receiver unit 15 is implemented in such a manner that it observes the frequency 110.7 MHz, which in practice means the observation of the listening to the radio station R3 in a vehicle.

In the following, the structure of the first receiver section 151 of the radio receiver unit 15 will be described. The given reference numerals are the same for the other receiver sections 152 and 153 as well. The first receiver section 151 of the radio receiver unit 15 comprises a pre-stage connected to an antenna means 160, this pre-stage comprising a pre-amplifier 161a and a filter 161b, which are adjusted to the leakage radiation frequency 100.7 MHz of the local oscillator, this frequency corresponding to the radio station Rl, most preferably in such a manner that the receiver section 151 receives frequencies on a narrow bandwidth around said frequency 100.7 MHz. Furthermore, the first receiver section 151 comprises a local oscillator 162, a mixer 163, an intermediate frequency filter 164, a detecting means 165, and a filter 166, in connection of which is also provided a pulse detecting means 167. It should be pointed out in this connection that the local oscillator 162 of the receiver section 151 of the radio receiver unit 15 described above should not be conceptually mixed up with the local oscillator 2 of the radio receiver 2 of the vehicle in Figure 5.

In Figure 4, the frequency of the local oscillator 162 of the receiver section 151 of the radio receiver unit 15 of the equipment is mixed in the mixer 163 with the received frequency, i.e. with the frequency propagating from the antenna 160 to the pre-stage 161a, 161b, this frequency thus being the frequency of the leakage radiation signal of the local oscillator of the radio receiver of the vehicle. In the case of the first receiver section 151, this frequency is the frequency 100.7 MHz, which is dependent on the transmit frequency 90 MHz of the radio station Rl. The result of the mixing is an intermediate frequency, which is separated with the intermediate frequency filter 164. After the intermediate frequency filter 164 is provided the detecting means 165, which is most preferably an AM detector. The envelope of a transmission which is at the desired frequency (at the frequency 100.7 MHz in this case) is obtained from the output of the detecting means 165, this envelope being for instance the envelope 170 or the envelope 180, which are shown in Figures 7 and 8, respectively. The obtained signal is filtered by a suitably dimensioned filter 166, which reduces possible disturbances.

In the envelope 170 of Figure 7, the mere detected passing local oscillator signal B appears at the frequency 100.7 MHz. The duration of a pulse depends for instance on the type of the antenna 16 of the equipment and the speed of a vehicle. The duration of a pulse is typically for instance 1 second. The envelope 180 of Figure 8 includes the combined effects caused by a radio transmission disturbing in the background and a local oscillator signal B passing the measuring point. Since the possible disturbing transmission is usually frequency-modulated in the FM range, its amplitude is constant and causes the bottom level 190 of the envelope to rise. The pulse detecting means 167 such as a detecting circuit is implemented in such a manner that it is able to eliminate this rise of the bottom level, and it indicates the appearance of the envelope pulse according to Figure 7. The elimination of the bottom level is implemented for instance in such a manner that the bottom level 190 is detected with the detecting means 167, and this level is set as a comparison level for pulse detection. A pulse 300 is obtained from the output of the detecting circuit 167 included in the first receiver section 151 of the radio receiver unit 15 of the equipment every time the receiver section 151 detects the local oscillator signal B which passes the measuring point and which appears at the frequency in question (100.7 MHz). Correspondingly, the pulse 300 is obtained from the output of the detecting circuit 167 included in the second receiver section 152 of the radio receiver unit 15 of the equipment every time the receiver section 152 detects the local oscillator signal B which passes the measuring point and which appears at the frequency in question (105.7 MHz). Correspondingly, the pulse 300 is obtained from the output of the detecting circuit 167 included in the third receiver section 153 of the radio receiver unit 15 of the equipment every time the receiver section 153 detects the local oscillator signal B which passes the measuring point and which appears at the frequency in question (110.7 MHz). Each detected local oscillator signal produces a pulse from the radio receiver unit 15, this pulse indicating what radio station was listened to in the vehicle. These pulses are stored in the memory and used in the calculation of the total number of listeners for instance by means of the microcomputer 18 or in some other similar way. Pulse indication can also be carried out for instance by a microprocessor by means of a suitable algorithm. With reference to Figure 5, due to the structure of the mixer in the radio receiver A of the vehicle, the signal of the local oscillator 2 also includes harmonic frequencies of the basic frequency in addition to this basic frequency, it being also possible to measure these frequencies. The use of these harmonic frequencies in the solution of the invention is also possible.

Even though the invention has been described above with reference to the examples according to the accompanying drawings, it will be apparent that the invention is not so restricted but can be modified in many ways within the scope of the inventive concept presented in the appended claims. If there are many, for instance 10, radio stations that one wants to observe, the radio receiver unit 15 is implemented as such that it can follow local oscillator leakage signals of ten different frequencies.

Claims

1. A method for conducting a survey among the listeners of radio stations, c h a r a c t e r i z e d in that the method comprises measuring the total amounts of listeners of radio stations by observing the leakage radiation signals of the local oscillators of the radio receivers of the vehicles passing the measuring point, this observation being carried out essentially simultaneously at several predetermined frequencies, which are dependent on the frequencies of the radio stations that one wants to observe, and that in the calculation of the numbers of listeners, the measurement result of the number of listeners of each radio station is increased when the leakage radiation signal of the local oscillator of the radio receiver of a vehicle passing the measuring point includes the information that the radio receiver of said vehicle was tuned in to the frequency of said radio station.

2. A method according to claim 1, c h a r ¬ a c t e r i z e d in that the proportions of listeners of several radio stations are determined on the basis of the measurement and calculation of the local oscillator signals, which are dependent on the frequency of the radio station which is being listened to in the vehicle.

3. A method according to claim 1 or 2, c h a r a c t e r i z e d in that a survey among the listeners of radio stations is conducted in a frequency band consisting of one or more units, this frequency band being entirely or partly comprehensive, and the lowest frequency of said frequency band being at least as low as the frequency of the radio station which has the lowest frequency added by the intermediate frequency of the local oscillator of the radio receiver of the vehicle, and the highest frequency of said frequency band being at least as high as the frequency of the radio station which has the highest frequency added by the intermediate frequency of the local oscillator of the radio receiver of the vehicle.

4. A method according to claim 1 or 2, c h a r a c t e r i z e d in that the information on the numbers and/or proportions of listeners, this information being measured by means of the method, is transferred to at least one of those radio stations the numbers of listeners of which are being measured.

5. A method according to claim 1 or 2, c h a r a c t e r i z e d in that the leakage radiation signals of the local oscillator of the radio receiver of the vehicle are observed with several antenna means, a common mode signal being produced from the signals received by the antenna means, and when this common mode signal is detected, the measurement result of the number of listeners of a radio station is increased.

6. A method according to claim 1, c h a r ¬ a c t e r i z e d in that observation is carried out in a tunnel which comprises a route along which vehicles move, this tunnel being for instance an underpass or passage tunnel or similar relatively disturbance-free environment.

7. A method according to claim 1, c h a r ¬ a c t e r i z e d in that the method also comprises observing by means of a sensor means whether there is a vehicle in the measuring area, and that the measurement result of the number of listeners of a radio station is only increased when it is noticed that there is a vehicle in the measuring area.

8. A method according to claim 1, c h a r - a c t e r i z e d in that the method also comprises acting in such a manner that a special observation person working at the special message terminal stores additional information relating to the vehicle which is located at the measuring point and/or persons located in this vehicle, and that this additional information is connected with the information on the frequency of which station the radio receiver of the vehicle was tuned in to.

9. A method according to claim 1, c h a r ¬ a c t e r i z e d in that the method also comprises recording vehicles that pass the measuring point with a camera means, and that the pictorial record created in this way is connected with the information on what radio station the radio receiver of the vehicle was tuned in to.

10. A method according to claim 1, c h a r ¬ a c t e r i z e d in that the observation of the leakage radiation signal of the local oscillator of the radio receiver of the vehicle is used for activating an information display means such as a billboard or some similar information display means.

11. A method according to claim 1, c h a r ¬ a c t e r i z e d in that the information on what radio station the radio receiver of the vehicle was tuned in to is stored as a time-dependent signal.

12. A method according to claim 1, c h a r ¬ a c t e r i z e d in that in order to eliminate disturbance signals, signals that are essentially symmetrical as to their amplitude peak are mainly observed in the method.

13. A method according to claim 1, c h a r ¬ a c t e r i z e d in that AM detection is used in the method for eliminating disturbance signals.

14. Equipment for conducting a survey among the listeners of radio stations, said equipment comprising a radio receiver unit (15, 151-153) and an antenna means (16) connected thereto, c h a r a c t e r i z e d in that the equipment or at least the antenna means (16) thereof is located in the vicinity of the roadway (10) along which vehicles (11-13) move; that the equipment comprises means for observing the leakage radiation signals (B) of the local oscillators (2) of the radio receivers of the vehicles passing the antenna means (16), this observation being carried out essentially simultaneously at several predetermined frequencies, which are dependent on the frequencies of the radio stations that one wants to observe; and that the equipment further comprises calculating means (18) connected to a radio receiver unit (15) for increasing the measurement result of the total amount of listeners of each radio station (Rl, R2, R3 ) when the frequency of the leakage radiation signal (B) of a local oscillator (2) received by the radio receiver unit (15) includes the information that said radio station (Rl, R2, R3) is being listened to in the vehicle (11-13).

15. Equipment according to claim 14, c h a r ¬ a c t e r i z e d in that the radio receiver unit (15) comprises an AM detector (165).

16. Equipment according to claim 14, c h a r ¬ a c t e r i z e d in that the equipment comprises several antenna means (16), which are connected via an adder means (27) to the radio receiver unit (15).

17. Equipment according to claim 14, c h a r ¬ a c t e r i z e d in that the equipment comprises a sensor means (29) for observing whether there is a vehicle (11-13) in the measuring area.

18. Equipment according to claim 14, c h a r - a c t e r i z e d in that the equipment comprises data transmission means (22, 23) for transmitting measuring data from the measuring area.

19. Equipment according to claim 14, c h a r ¬ a c t e r i z e d in that the equipment also comprises an information means (32) such as a billboard, and that the radio receiver unit (15) is connected to control the activation of the information means (32).