DE2350034A1 - PILOT SIGNAL DETECTION CIRCUIT - Google Patents

Description

PHN.6592 JW / FF / Gils

Dipl.-ing. "Henrich Hartmann 2350034

■: ... ν Ljl .'-.- λι..Ι cri :: Αο.Ίιtk

"! F .: PHU- 6592

Registration for Oct. 4, 1973

"Pilot signal detection circuit"

The invention "relates to a.

circuit with a filter for separating the Piiotasignal from a compiled signal, the filter output signal to the Controlling a pilot signal evaluation circuit used as well as one. Noise detector is supplied to avoid erroneous Pilot signal evaluation in the case of predominant noise signals is used.

A pilot signal detection circuit is used to detect the presence of a pilot signal in a received composite Signal.

In some cases, for example with stereo multiplex receivers, it is only desirable to detect the presence of the stereo pilot signal when the composite signal with sufficient strength, i.e. with a sufficiently high level of intoxication

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distance, is received. Once this is the case, just kick still a few problems to recognize the presence of the stereo pilot signal.

In contrast to this, with the circuit according to the invention intends to recognize the presence of the pilot signal as early as possible, i.e. already with the lowest possible signal-to-noise ratio. Such a circuit arrangement can be used for Detection of the 57 kHz pilot signal that is broadcast in the VHF range by those stations that do not have their normal entertainment programs regularly send traffic information. Of course, these tips are not only of interest to those which were irradiated in the by such a Terkrundfunksender Area, but also for those who want to go in the direction of such an area and it is therefore It is important to contact the traffic radio station concerned as early as possible to be able to find out from the number of other transmitter signals or by an automatic search arrangement of the receiver to be able to find out.

Hun it is not possible to filter out the pilot signal only with the help, for example, one or more cascaded selective circles and use it. If the modern receiver with a high high frequency gain, if they are not tuned to a transmitter signal, deliver such a high level of noise and interference within the passband of such a filter that an erroneous pilot message caused by these noise and interference signals would often occur. A significant reduction in the passband bandwidth of the filter (high selectivity) could eliminate this disadvantage, but then it has a low one

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The filter has already moved away from its nominal frequency for a long time, that a received correct pilot signal is no longer as such is recognized.

Therefore, "your pilot signal has already been identified suggested that he be a relatively highly selective one Filter the pilot signal enhancement circuit is controlled while at the same time there is a noise detector, which is somewhat selective Filter is controlled. If that is relatively highly selective If a signal passes through the filter, it will only be recognized as a pilot signal if at the same time the detection circuit sends a proportional signal emits low signal level "

However, it has been found that, in such cases, erroneous reports can be avoided completely. SslialtmEgsordnung the selectivity of the highly selective filter must be so high that the risk of losing the vote occurs again, while such a high selectivity also leads to extraordinary production costs (many necessary sp-alom). Off Bie invention Pilotsigaalerkennungsschaltung BESW © ckt ₉ these disadvantages, and it is this designated by an amplitude demodulator for demodulating the filter output signal, a first network, the pilot signal evaluation circuit is supplied with the substantially DC component of the amplitude-demodulated Pilterausgangssigsals, and a global network, with the at least part of the AC voltage components of the amplitude-demodulated filter output signal is fed to the Hausciadetektor.

That is required in the circuit arrangement according to the invention Filters can have a relatively low selectivity

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(Q »40), while the circuit arrangement also for for the most part can be easily integrated monolithically. Through the invention a very reliable and cheap pilot signal detection circuit is created.

TTm a certain traffic radio station for a traffic announcement to distinguish it from other traffic radio stations and / or to indicate whether the station in question is broadcasting a traffic notice or a normal (entertainment) program, this can transmitted pilot signal (57 kHz) still with one or more modulation signals (21 to 53 Hz) be modulated. In such a case, the pilot signal detection circuit according to the invention can Have characteristics that said second network is at least almost impermeable to the frequencies of the modulation signals is.

The output of the noise detector can be in two ways Wise to be used. The first way is that the pilot signal evaluation circuit, in addition to the DC voltage component of the amplitude-demodulated filter output signal at the same time the output voltage of the noise detector is fed. The second way consists that the output voltage of the noise detector is used as a gain control voltage to regulate the gain of the Filter the amplitude demodulator supplied signal is used.

An embodiment of the invention is shown in the drawing and is described in more detail below. Show it:

1 shows a block diagram of an embodiment of a radio receiver with an inventive Pilot signal detection circuit,

Fig. 2 and 3 some diagrams to explain the effect

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235C034.

way of the circuit arrangement according to fFig. 1.

Fig. 1 shows a VHF broadcast receiver with an antenna 1, an RF amplifier and a tuning unit 2, an IF amplifier 3, a frequency demodulator 4 »an LF amplifier 5 and a Loudspeaker 6. In the case of a stereo receiver, the audio amplifier contains nor a stereo decoder "with double audio channels, which are followed by at least two loudspeakers.

Some of the transmitters that the receiver will be tuned to can, can in addition to the normal entertainment programs, if necessary Send announcements at regular times that are important for traffic in the coverage area of the station in question. Such a so-called traffic radio transmitter sends a pilot signal of, for example, to distinguish it from the other transmitters 57 kHz in its modulation signal. In order to be able to recognize whether the receiver may have been tuned to a traffic radio station the receiver of Fig. 1 is provided with a pilot signal detection scarf device 7, which is connected to the output of the frequency demodulator 4.

The pilot signal detection circuit 7 includes a filter 8, which is tuned to the pilot frequency and has a passband width of 1.4 kHz (Q = 40), for example. The output signal of the filter 8 is fed to an amplitude demodulator 10 after amplification in an amplifier 9.

The DC voltage component is transmitted via a smoothing network 11 V of the output signal V of the amplitude demodulator 10 is fed to a pilot signal evaluation circuit 12. With this circuit, which can be a trigger switch, for example, takes place actual determination of whether in the output signal of the frequency demodulator

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tor 4, if necessary, a pilot signal is available.

A high-pass filter 13 serves to remove at least some of the AC voltage components that are present at the output of the demodulator 10 are to be let through. These alternating voltage components, the noise and Interference signals are caused, are amplified in an amplifier 14 and then in a so-called noise detector 15 with a subsequent smoothing network 16 rectified. The DC voltage T. obtained in this way also becomes the pilot signal evaluation circuit 12 supplied as a comparison voltage. The circuit arrangement 12 controls an indicator lamp 17.

To explain the mode of operation of the circuit arrangement according to FIG. 1, the diagrams in FIGS. 2a, 2b and 2c are used Output signal V of the amplitude demodulator 10 for the three following Cases indicated.

The diagram in FIG. 2a shows this voltage if, for example, no transmitter signal is received and the noise and interference level is high as a result. The DC voltage _{component T Q of} the voltage T has approximately the same magnitude * as the AC voltage amplitude V. The equalization circuit 12, which equates the voltage T "and the DC voltage T ₁ derived from the AC voltage amplitude 7, is now designed in such a way that in this case no The indicator lamp lights up.

Fig. 2b shows the case in which it is tuned to a transmitter signal, but this is not due to a traffic broadcasting station het and therefore does not contain the 57 kHz pilot signal. Of the Noise and interference levels within the passband of the filter 8 is now much lower, but the alternating voltage amplitude

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T of the amplitude demodulated filter output is still of the same size as its DC voltage component V-. The comparison circuit 12 will therefore still not cause the indicator lamp 17 to light up.

If a transmitter signal is received that is a 57 kHz pilot signal contains, the amplitude demodulator 10 supplies a voltage like this one in Pig. 2c is shown. The direct voltage component V_ is now much larger than the alternating voltage amplitude Y and the evaluation circuit 12 is set up such that the indicator lamp 1? now lights up.

From the above it should be evident that without the use of filters with high selectivity one is very reliable functioning pilot signal detection circuit has been obtained. Essentially the only remaining option is one incorrect message that an interfering signal with the character of a continuous oscillation within the bandwidth of the Filters 8 occurs. The risk of such a disruption is in the Practice, however, is extremely low.

The evaluation circuit 12 can be designed in many ways. Instead of directly comparing the two input voltages V _Q and V with one another, as has been described above, the circuit arrangement 12 can have its own suitable threshold value for each of the two inputs. Only when the voltage V .. is below and the voltage V _{Q is} above the relevant threshold voltage, the lamp 7 lights up.

_{The direct voltage V 1} originating from the bulk detector 15 can be fed to the amplifier 9, for example, as a gain control voltage instead of the evaluation circuit 12. This is in Pig. 1

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indicated by the dashed line connection 18. If a lot of noise and interference signals pass through the filter 8 (FIG. 2a), the resulting high voltage V .. will reduce the gain of the amplifier 9. At the same time, this reduces the DC voltage V _{n of} the amplitude-demodulated voltage V. For the three cases described, this voltage now has the shape shown in FIGS. 3a, Jb and 3c. The evaluation circuit 12 can now consist of a trigger circuit with a permanently set threshold value V, which only lights up the indicator lamp 17 if the direct voltage V _Q is greater than the threshold voltage V, - It has already been proposed to use the pilot signal with median frequency tones for traffic radio stations (in the frequency range from 21 to 53 Hz) so that the different traffic radio stations can be distinguished from one another and / or to indicate whether the traffic radio station is sending a traffic announcement. In order to prevent the pilot signal recognition circuit 7 from evaluating such tones as interference signals and therefore indicating the absence of a pilot signal while it is still present, the high-pass network 13 is dimensioned with a limit frequency above the highest of the mentioned tones (53 Hz). These low-frequency tones can therefore not pass through the high-pass network 13 and they do not influence the effect of the noise detector 15.

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Claims (3)

- 9 ■ - PH5.6592 patent claims ι 1.) Pilot signal detection circuit with a filter for separating the pilot signal from a composite signal, wherein the pilter output signal for controlling a pilot signal evaluation circuit used as long as it is fed to a noise detector, which is used to avoid incorrect pilot signal evaluation in the event of (strong) Hauschen is used, characterized by an amplitude demodulator (10) for demodulating the filter output signal, a first network (11), with essentially the DC voltage component of the amplitude-demodulated Filter output signal of the pilot signal evaluation circuit (12) is fed, and a second network (13) with the at least some of the AC voltage components of the amplitude-demodulated Filter output signal fed to the noise detector (15) will. 2. Pilot signal detection circuit according to claim 1, for detecting a pilot signal, the one or more modulation signals can be modulated on, characterized in that the second network (13) for the frequencies of the modulation signals at least is almost 'impermeable. 3. pilot signal recognition circuit according to claim 1, characterized characterized in that the pilot signal evaluation circuit (12) in addition to the DC voltage component of the amplitude-demodulated filter output signal at the same time the output voltage of the noise detector (.15) is supplied will. . 4 · pilot signal detection circuit according to claim 1, characterized characterized in that the output voltage of the noise detector (15) is used as a gain control voltage to regulate the gain of the over the filter (8) the amplitude demodulator (1O) fed signal serves. 409819/068 8 . ■ ^Ä · Blank page