Note: Descriptions are shown in the official language in which they were submitted.
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PROCESS AND DEVICE FOR THE RADIO TRANSMISSION OF CODED
D.~TA SUPERIMPOSED 0~ A TRADITIONAL FREQUENCY-~ODUI.~TED
BROADCAST
The present invention relates to a process and
a device for the radio transmission of coded data super-
imposed on a traditional frequency-modulated broadcast.
The invention relates more particularly to a
process for the radio transmission of coded data super-
imposed on a traditional frequency-modulated broadcast
wherein coded data to be transmitted are modulated in a
predetermined frequency range in order to create
modulated coded signals, the modu]ated coded signa]s are
mixed with the low-frequency signals of a traditional
program to be broadcast by a frequency modulation radio
transmitter, the signals delivered by a frequency
modulation receiver are filtered in order to isolate the
said modulated coded signals, the filtered, modulated
coded signals are demodulated and the transmitted coded
data are displayed or recorded by applying the demodulated,
filtered coded signals to a display or recording unit.
A variety of systems for the radio transmission
of coded data are already known. In general, these
systems constitute warning ~r watching devices
and require the existence of transmitters and receivers
specially designed for the transmission of coded data.
Furthermore, attempts have already been made to
superimpose, on a conventional radio broadcast, certain
signals for controlling particular functions. However,
applications of this type are very specific and do not
permit the reception and display, in uncoded form, of
coded data which are capable of complementing the content
of audio data transmitted conventionally by radio waves.
It has also been proposed to superimpose coded
data on a conventional frequency-modulated radio broad-
cast by adding a low-level subcarrier modulated by coded
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signals. However, the proposed systems have not as
yet made it possible to obtain reliable transmi.ssions
without substantially impairing the main program or
the additional coded signals.
The precise aim of the present invention is to
overcome the abovementioned disadvantages and to make
it possible, without impairing the quality of a con-
ventional frequency-modulated radio broadcast, reliably
to transmit supplementary coded data which are capable.
of complementing the conventional radio broadcast.
These objects are achieved by virtue of a pro~
cess of the type defined at the start of the description,
wherein the coded data to be transmitted are modulated
by frequency shift in a frequency range located between
about 15 and 18 kHz, wherein the coded signals modulated
by frequency shift are mixed, with an attenuation of
20 to 40 dB relative to the maximum transmission level,
with the said low-frequency signals of a traditional
program, and wherein the ratio of the frequency devia-
tion of the coded signals modulated by frequency shift,
expressed in Hertz, to the rate of transmission of the
coded data to be transmitted, expressed in bauds, is
kept between about 85 and 120% and preferably around
100%.
Preferably, the signals modulated by frequency
shift are applied downstream of the stereophonic filters
of the frequency modulation transmitter in order to mix
the said modulated signals with the signals of a
traditional radio program.
Advantageously, the reception signals to be
filtered are tapped upstream of the de-emphasis circuits
of the standard frequency modulation receiver.
The demodulated filtered reception signals can
be displayed on a data processing terminal, which makes
it possible to control the checking of the filtering
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characteristics.
According to the invention, a device ~or the
radio transmission of coded data superimposed on a
traditional frequency-modulated broadcast comprises an
input unit for generating coded data to be transmitted,
an FSK coder-modulator for modulating, by frequency
shift, the coded data to be transmitted, in a frequency
range located between about 15 and 18 kHz, a mixer
circuit for superimposing, with an attenuation of 20 to
40 dB, the signals modulated by frequency shift on a
low-frequency signal of a traditional program to be
applied to a requency modulation radio transmitter, a
decoder comprising filter circuits and an FSK de-
modulator for separating the coded data from the signals
delivered by a standard frequency modulation receiver,
and a display or recording unit for displaying or re-
cording the demodulated, filtered, transmitted coded
data.
The display unit can be a standard television
receiver or the display unit of a data processing
terminsl equipped with an outlet for peripherals and, if
appropriate, with an adapter circuit. A link can be
provided between the said data processing terminal,
displaying the transmitted coded data, and the program-
mablefilters of the decoder for sending out programmable
check codes.
The decoder also comprises a level adapter
arranged at the input and two level-checking units
arranged on either side of the filter circuits.
The device according to the invention is
suitable for the transmission of coded data representing,
for example, the title of a record, an advertising
message or commercial information.
The coded message, which is prqferably trans-
mitted repetitively with the aid of a loop broadcast,
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can comprise various check characters or coded charac-
ters which cannot be displayed.
Further characteristics and advantages of the
invention will become apparent from the following des-
cription of embodiments of the invention, with referenceto the attached drawing; in this drawing:
- Figure 1 schematically represents the
.various items of equipment to be used for the broadcast
part of a transmission device according to the invention,
- Figure 2 schematically represents the various
items of equipment to be used for the reception part of
a transmission device according to the invention,
- Figure 3 is the block diagram of the recep-
tion part of a device according to the invention,
- Figure 4 shows an embodiment of a coder-
modulator circuit which can be incorporated in the
broadcast part of the device according to the invention,
- Figure 5 shows an example of filter and de-
modulation circuits of a decoder which can be incorpora-
: 20 ted in the reception part of the device according to
the invention, and
- Figure 6 shows a curve of the average re-
cording level of a music signal as a function of the
frequency.
Referring to Figure 1, this figure shows a con-
ventional frequency modulation transmitter 20 equipped
with an antenna 21 and intended for receiving, via a
line 11, low-frequency electrical signals representing a
radio program to be broadcast and originating from a
microphone or from a system for reading recorded informa-
tion, such as a record player turntable 10 or a tape or
cassette recorder. In the absence of any other device,
~ the radio program is simply transmitted conventionally
; by the FM transmitter 20 and its antenna 21.
Accordin3 to the inveotion, before the frequencJ-
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modulated broadcast, coded digital signals are super-
imposed, in a mixer 32, on the program signals applied
via the line 11, so that the FM transmitter then receives
a mi~ture of conventional low-frequency signals and
coded signals via the line 33.
The coded signals can be formed very easily
from messages in uncoded form with the aid of a con-
ventional data processing terminal 40 equipped with a
keypad and capable of delivering, via a line 41, signals
coded according to a preset code, for example in RTTY
code according to an RS 232 format. The terminal 40 can
include a conventional unit for the storing and manage-
ment of texts.
The coded signals can also originate directly
from a memory or other recording medium. In one possible
application, the coded signals can be formed from the
reading of a bar code with the aid of an optical reading
device. In another application, the coded signals can
consist of coded signals which are non-decodable after
radio transmission but which are already present in the
recording medium read in the reading device 10 for the
radio broadcast by the transmitter 20. In this case,
the signals produced by the reading device 10 can also
be applied, via the line lla, to a decoder 12 suitable
for decoding coded magnetic tapes, cassettes or discs.
The signals produced by the decoder 12 via the line 41a,
which comprise a coded message, can then be used to feed
into the coder 30 provided for receiving the coded
signals transmitted via the line 41.
The coder 30 essentially comprises a modulator
34 of the FSK type (frequency shift Keyin~) so that
it can transmit, via the line 31, coded signals charac-
terized by two predetermined frequency levels. According
to the invention, the FSK modulator 34 is designed so
that the frequency levels of the coded signals are
125392~
loca~ed between about 15 kHz and 18 kHz and so that the
level of the coded signals in the line 31 is attenuated
by 20 to 40 dB in order to take account of the curve
of the level of the LF signals usually transmitted via
the line 11 (see Figure 6). Thus, after mixing in the
mixer 32 with the LF signals present in the line 11,
the coded signals in the line 31 do not affect the
quality of the conventional radio broadcast, nor are
they suppressed by the filters of the conventional
frequency modulation transmitters or receivers.
It is pointed out that, in an advantageous
variant, the coded signals can be introduced directly
into the FM transmitter 20, via the line 31a shown as
a broken line in Figure 1, downstream of the stereo-
phonic filters. In this case, the mixer 32 of Figure1 is naturally suppressed and the line 33 transmits the
same signals as the line 11. The reinjection of coded
signals after the stereophonic filters of the FM trans-
mitter makes it possible subsequently to facilitate
separation of the coded signals on reception, by virtue
of the gain obtained in the frequency band of the FSK
modulated coded signals.
Figure 2 schematically represents the components
of the recep~ion system of a device according to the~
invention. These components essentially comprise a
standard frequency modulation receiver 120 with its
antenna 121, a decoder 50 and a display unit 60, which
can be a standard television receiver or a data pro-
cessing terminal equipped with an inlet for peripherals.
The signals applied to the decoder 50 can be tapped from
an audio outlet via a line 51 or, preferably, via a line
51a shown as a broken line in Figure 2, before the de-
emphasis circuits of the receiver 120, which affords a
gain of the order of 10 to 15 dB in the frequency band
containing the coded signals.
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The coded signals, which, in the decoder 50,
are separated from the conventional radio message, are
applied to the display unit 60 via a line 52 and can
then appear in uncoded form on the screenA At the same
time, the listener can listen to the usual radio
program. Of course, the decoder 50 can be integrated
into the housing of the FM receiver 120 if required.
Furthermore, in the case where the display unit 60 con-
sists of a data processing terminal, it is also possible
to send coded check signals to the decoder 50 via the
line 53 from the terminal 60 in order to be able to
adapt to different reception circumstances a~d to con-
trol, for example, the programming of the quality
factcr or of the central frequency of the filter con-
tained in the decoder.
A recording unit consisting of a memory, for
example, can be substituted for or associated with the
display unit 60 for recording the coded signals produced
by the demodulator 50.
Figure 3 shows the components forming the de-
coder 50. A level adapter 55 receives, via an input
capacitor 54, the complex signals delivered via the
lines 51 or 51a by the FM receiver 120, as indicated
previously. The output of the level adapter 55 is con-
nected to filter circuits 56, which are preferably
program~able capacitor switched bandpass filters,
associated with a clock 57. The filters can be
programmed permanently with the aid of keys, but the
programming can also be adapted by the user if the unit
60 consists of a data processing terminal.
Level-checking components 63, 64 are arranged
respectively before and after the filter circuits 56.
A phase loop FSK demodulator 58 is placed at the output
of the filters 56, and error correction circuits 59,
sensitive to coded error correction signals, can be
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placed at the output of the FSK demodulator 58 i~
required. Adapters 61, 62, which depend on the type
of display unit 60, are inserted between the output of
the decoder 50 and the lines 52a, 52 respectively,
which are provided for connection to two display units
60 of different types.
Figure 4 shows a particular example of an FSK
modulator which can be incorporated in the coder 30 of
Figure 1. This modulator 34 is constructed around a
standard base circuit, for example the XR2206 circuit
from the Company EX~R, and has characteristics which can
be adapted with the aid of external resistors and
capacitors. The coded signals are applied to the input
35 and the sinusoidal FSK modulated output signals are
available at an output 36. Square-wave output signals
are available for checking purposes at an output 37.
As can be seen in Figure 4, the FSK modulator 34 can
comprise a base circuit with current interrupters, 131,
a voltaae controlled oscillator circuit (VC0) 132 and
a multiplier circuit 133 which also converts the signals
to sinusoidal form. The external components can then
comprise resistors or potentiometers 141 to 144 and a
frequency-regulating capacitor 145, resistors or poten-
tiometers 151 to 153 and a capacitor 154 for regulating
the output signal level, and resistors or potentiometers
161, 162 for adjusting the shape and symmetry of the
sinusoidal output signal with the aim of obtaining
minimum distortion.
To have a good signal-to-noise ratio and to
reduce intermodulation, it is desirable for the ratio
of the frequency deviation of the signals modulated by
frequency shift, expressed in Hertz, to the rate of
transmission of the coded data to be transmitted, ex-
pressed in bauds, to be between about 85 and 120% and
preferably around 100%. Thus, with a transmission rate
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of 300 bauds, it is desirable for the frequency shift
caused by the FSK modulator to be, for exampl~, +150 Hz.
Figure 5 shows, in greater detail, an embodi-
ment of a decoder-demodulator circuit 50 with a clock
57 comprising a frequency reference component 70,
connected in parallel with a capacitor 71, and reversing
logic gates 73, 74, 75 associated with resistors 7J,
79, capacitors 72, 78 and an output circuit 76 consis-
ting of a frequency divider (dividing by 9 for example),
which makes it possible for example to deliver clock
pulses of the order of 1 MHz at a frequency of 8 MHz
divided by 9.
The filter circuit system 56 comprises first
and second switched capacitor filters 56a, 56b,
which can consist, for example, of the R562~
circuits from the Company RETICON. The characteristics
of the programmable filters 56a, 56b can be determined
by interrupters, as shown in Figure 5, or by control
signals produced by the terminal 60, as indicated pre-
viously. The filters 56a, 56b can be of the bandpass
or high-pass type.
The demodulator 58 shown in Figure 5 is of a
conventional configuration with an input preamplifier
81, a voltage controlled oscillator circuit (~7CO) ~0, a t~hase
detector 82 and a quadrature detector 83, a locking
detection filter 84, loop and data filters 85, 86, a
comparator for detecting a locking condition, 88, an
internal reference circuit 89 and an FSK comparator 87
delivering output signals corresponding to the de-
modulated, transmitted coded signals.
It is desirable if the coded data to be trans-
mitted are transmitted according to a repetition loop.
Furthermore, the transmitted coded message will
advantageously comprise check characters including an
image clearing code, placed before each phase of the
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message, as well as an end-of-message signaling code.
In one possible application, the transmitted
coded message comprises coded characters which cannot
be displayed and the transmitted coded characters which
S cannot be displayed are recorded by applying the de-
modulated filtered signals to a memory unit. This can
contribute for example to facilitating the measurement
of the ratings of radio stations identified by a par-
ticular code.
The invention is particularly suitable for the
use of the decoder-demodulator in combination with a
personal data processing terminal such as, for example,
the one known as ALCATEL 250. In this case, it is
desirable for the check characters to include a charac-
ter which ensures that the personal terminal is in the
scroll mode.
