Patent GB-1151710-A (GB)
Title: Improvements relating to Systems for Determining the Listening Habits of Wave Signal Receiver Users
IPC: C07C233/02
Filed: 1966-09-13
Abstract: 1,151,710. Recording use of receivers; switching circuits. FREDERIK ADOLF NAUTA, and FREDERICUS ALBERTUS BECHT, [trading as INTOMART, INSTITUT VOOR TOEGEPAST MARKTONDERZOEK]. 13 Sept., 1966 [14 Sept., 1965; 25 Aug., 1966], No. 40923/66. Headings H3Q and H3T. To record the use of a radio receiver by means of attached registering apparatus the transmissions contain special registration signals consisting of combinations of sinusoidal signals of 150 c/s. or lower, and the registering apparatus operates only while these frequencies are being transmitted. In Fig. 1 the signals at the loudspeaker terminal 1 of the receiver are passed via limiting diodes and a preamplifier 4 to two parallel amplifiers 8, 9 tuned respectively to two low audio frequencies, e.g. 70 c/s. and 90 c/s. Each amplifier contains a twin-T R.C. filter in a negative feedback path to a transistor 19 which is emitter-coupled with the input transistor 10. If both frequencies are present in the input, each amplifier produces an output and the seriesconnected transistors 30, 32 will both conduct, allowing the potential at point 33 to rise to near earth potential. This rise is passed through capacitor to cut off transistor 36 and turn on transistor 38, allowing the recording motor M to run. After a certain time (e.g. 5-10 sec.) capacitor 34 has discharged sufficiently to allow transistor 36 to conduct, cutting off 38 and stopping the motor. The outputs of the amplifiers are also applied to the recording head 44 via transistor 43. In another form (Fig. 2) the signal 1 is passed to two tuned relays 123, 124 which oscillate and pass voltage through their contacts and the smoothing circuits to the input of an amplifier 140. If both relays oscillate, the output of the amplifier is sufficient to operate relay 118 and start the motor M. Contact 120 then changes over and the amplifier input is maintained by the voltage on capacitor Cx until this voltage has leaked away. The voltage at the oscillating contacts is also passed to the recording head 107. In another version (Fig. 3, not shown) the tuned relay contacts are on the same magnetic core and send pulses to turn on a thyristor (145). After a certain time a contact (144) on the recording tape discharges capacitor (CX) and cuts off the thyristor. A combination of three frequencies may be used (Fig. 4, not shown). Data handling.-Six basic frequencies are used, of which two or three are transmitted at any instant. One such combination starts the recording as described above while the others identify particular programmes, followed by a blank to signify the end. Every so often, the tapes are sent in to a central station where they are played back in the reverse direction at 100 times the speed, the data being transferred directly to a computer. To synchronize the speeds of recording and playback a mainsfrequency signal is injected into the tape while recording. This can be a hum signal present in the receiver, and a filter is included to prevent it reaching the loud-speaker.