DE2265498B1 - Procedure for marking traffic broadcasting areas - Google Patents

Description

The invention relates to a method for identifying traffic broadcast areas in the VHF broadcast transmission system according to the features of the generic term of claim 1.

In the course of the development of a traffic broadcast system it has been found to be useful to use the spatially distributed traffic radio transmitters in VHF radio transmission systems to broadcast only those traffic messages that concern the surrounding region. But since the The reception areas of these traffic radio stations extended beyond this respective region The 57 kHz subcarrier alone is no longer sufficient to identify traffic radio stations. It turned out hence the task of developing a method by means of which the individual regional traffic broadcasting areas in addition to the identification by the 57 kHz subcarrier, continuously or at least during transmission the traffic messages themselves can be distinguished without affecting the rest of the broadcast influence.

From DE-OS 20 61876 is a system for Radio transmission of messages is known in which messages pertaining to individual geographical zones are transmitted one after the other by means of a carrier. These for the medium or long wave range On the one hand, the system provided for lying transmitters does not allow simultaneous notification of several regions With the particular messages for this too, it also doesn't allow just the traffic messages select and switch through that apply to a certain of the various regions.

DE-OS 2045 342 discloses a method for automatically switching one to the program broadcast a transmitter coordinated receiving device to warn another warning transmitter known. Here, for warning broadcasts from the other warning transmitter, the one known for FM stereo broadcasts is used The pilot oscillation of the currently received transmitter is amplitude-modulated with an auxiliary oscillation. The auxiliary signal derived therefrom becomes a control signal for switching over to the warning transmitter derived. This method is not intended to mark traffic information areas in the VHF band suitable.

In order to solve the problem, a committee appointed for this purpose proposed to each traffic broadcasting area assign a frequency combination of 2 or 3 frequencies as a code signal, the frequencies of which are all below 200 Hz and these to the 57 kHz carrier are continuously as frequency modulation to be modulated with a stroke of max. 1 kHz. In testing this procedure, however, shown that the frequency modulation of the subcarrier leads to unacceptable interference in the broadcasts and that the evaluation of the frequency modulation of the subcarrier on the receiver side a relatively high effort is required.

To identify the start of a traffic message as a so-called message identifier, the same should be used Proposal for the 19 kHz stereo pilot tone to be switched off.

It has now been found, surprisingly, that the disadvantages of this proposal found during testing in the method according to the invention, which is indicated by the characterizing part of claim 1 Characteristics is marked, do not occur, even if the characteristic frequencies are already in Base area. On the other hand, the characteristic frequencies that are broadcast with the traffic messages below the listening area for traffic announcements to avoid interference as indicated whose lower cut-off frequency is approx. 175 Hz. Advantageous further developments of the method according to the invention are set out in the subordinate claims refer to.

The following is an example of a method according to the invention based on a drawing of an evaluation circuit described.

The method is based on the assumption that all transmitters which broadcast traffic information are identified with a subcarrier Tu with a frequency of 57 kHz. The entire transmission area is now divided into individual traffic radio areas, each traffic radio area being assigned a code frequency (fi) which is below the listening area. The subcarrier Th is modulated in amplitude with the characteristic frequency assigned to the corresponding traffic radio area. This ensures reliable identification of the traffic radio transmitter on the one hand and the traffic radio areas on the other. By means of a radio receiver that has a suitable evaluation circuit, it is now possible to set or recognize only the respective, desired traffic radio range.

Such a particularly advantageous evaluation circuit is described in more detail below.

For the characteristic frequencies 4, the frequencies are chosen so that the filter is at a Q = 20

ORIGINAL INSPECTED

the evaluation circuit in a radio receiver results in a neighboring selection of <15 dB. Furthermore, the Kennf are equenzen ^r 4 is selected so that the harmonic of the characteristic frequencies 4 between the actual characteristic frequencies lie 4. This results ^r> a low interference.

Message identifier is used to indicate the beginning and end of traffic information. This message identifier MK can, for. B. a recording device can be switched on and off or a radio receiver switched to forced announcement.

A frequency of 21 Hz is selected for the message identifier MK , while the characteristic frequencies are 4 for the traffic information area identifier 45 and 53 Hz. These two frequencies are obviously already in the baseband. However, since - as is generally known - the baseband is not fully used up to the lower end in voice broadcasts and thus also in traffic news, it is possible, as indicated, to also select the characteristic frequencies above 40 Hz. On the other hand, they are chosen so that they remain below the listening area for traffic reports.

The evaluation circuit shown in the drawing for a method according to the invention can be relatively easy to implement and combine with a radio receiver.

If a radio receiver receives a transmitter that is identified by a subcarrier 7 »as a traffic radio transmitter, the subcarrier Tu is after demodulation of the received transmitter signal from the low frequency, z. B. music or speech, separately and fed to a detection circuit 1. This detection circuit 1 affects z. B. an electronic station search and indicates that a traffic information station is being received. Furthermore, the 57 kHz subcarrier T _{H is} demodulated in) 5 of the detection circuit 1, as a result of which the characteristic frequencies 4 of the individual traffic radio areas are obtained. This characteristic frequency 4 is now fed to a Schmitt trigger 2, constructed in a known manner, which converts the sinusoidal characteristic frequency 4 into a square-wave pulse voltage. The pulse voltage obtained in this way is fed to a mono-flop 3 and converted into a pulse voltage with a constant pulse width. In an integration stage 4 connected downstream of the mono-flop 3, the pulse voltage is integrated with a constant pulse width and the frequency of the characteristic frequency 4, so that a voltage Uk is produced at the output of the integration stage 4 which is proportional to the characteristic frequency 4. This voltage ίΛ is now fed to the display device 5 of a radio receiver via a switch S. The display device is constructed with a display scale 7 made up of luminous elements 6. In addition to the usual frequency markings, the scale also has markings for the traffic radio areas. If the voltage Uk is fed to the display device 5 instead of a tuning voltage Uaösi of an electronically tuned radio receiver, the light element (s) 6 which correspond to the frequency 4 of the traffic radio range lights up. This provides a simple but effective way of recognizing the traffic radio range received in each case.

In a further development of the invention 5 traffic radio area buttons 8 are now coupled to the display device, which allow only stations of a certain traffic radio area to be received. Each traffic radio area is assigned an area button 8, which is connected to a transmitter search circuit in such a way that the transmitter search tunes the receiver only to transmitters which send out a subcarrier Th which is amplitude modulated with the frequency 4 assigned to the preselected traffic radio area.

Furthermore, the detection circuit 1 is followed by a filter 9 which filters out the message identifier MK. The message identifier MK, which marks the beginning and end of a traffic message, can be used after appropriate processing to record a recording device, e.g. B. turn a cassette tape recorder on and off, or forcibly switch a radio receiver for the traffic message.

The evaluation circuit can be set up without complex filters and is easy to use with a To combine radio receivers that are tuned electronically with an automatic station search system is provided and has a display device which is constructed with luminous elements.

1 sheet of drawings

Claims (4)

Patent claims: 1. Method for the identification of traffic broadcasting areas, in the VHF broadcasting system, in which the respective traffic radio transmitter in the VHF range is frequency-modulated with a baseband which also contains traffic information and which contains a total signal band of 40 Hz to 15 KHz, and the traffic radio transmitter for identification is one above of the listening area {57 KHz) lying subcarriers and each traffic broadcasting area is assigned a frequency with which the subcarrier is modulated, characterized in that the subcarrier (Th) modulating the amplitude frequency (ίκ) are selected so that they are below the Listening range for traffic messages lie that a sufficient neighbor selection is achieved and that harmonics of the characteristic frequencies (ίκ) lie between the characteristic frequencies. 2. The method according to claim 1, characterized in that frequencies above 40 Hz are selected for the characteristic frequencies (ίκ). 3. The method according to claim 1 or 2, characterized in that one of the identification frequencies is used as a message identifier (MK) for a traffic news broadcast and at the same time one of the other frequencies is used as an area code and that the message identifier is the same for all traffic radio areas. 4. The method according to claim 1, 2 or 3, characterized in that frequencies of 45 Hz and 53 Hz are selected for the characteristic frequencies (ίκ).