DE1030880B - Facility for telephony over a channel with a relatively narrow bandwidth - Google Patents

Description

GERMAN

The invention relates to a device for telephony in which only a very narrow band of a few 10 ¹ Hz is used for the transmission of speech.

It is known that a telephone signal can be expressed by the following equation:

s (t) = α {t) cos [φ {t)], (1)

where a (t) and φ (t) correspond to the amplitude and the phase of the signal and are shown in analytical form. ίο

With the signal expressed by the equation (1), it becomes more to be described by means of corresponding ones electronic devices kept the amplitude constant, so it can be deduced that the entire message in the expression

cos [ψ (t)]

(2)

is included.

Thus, when the voltage represented by the expression cos [φ (ί)] is applied to a loudspeaker, the speech is reproduced in such a way that all words appear understandable and preserve their tonal character. With a constant amplitude, the dynamic character of the speech is lost, but this loss has no effect on the intelligibility of the speech.

According to the invention, the telephony signal α (t) cos [φ (t)] is first converted into a single sideband on a carrier wave of the angular frequency ω and assumes the following expression:

Telephony facility

over a channel proportionately

narrow bandwidth

Applicant:

Jean Camille Pierre Marcou
and Jacques Daguet, Paris

Representative: Dr. M. iEule, patent attorney,
Munich 13, Kurfürstenplatz 2

Claimed priority:
Belgium 22 February 1955

Jean Camille Pierre Marcou and Jacques Daguet,

Paris,
have been named as inventors

α (t) cos [a) t + φ (t)] .

(3)

The angular frequency ω of the suppressed carrier wave used for transmission must be selected to be sufficiently high so that the bands of a [t) and cos [ω t -f- φ (t)] are far apart and do not overlap. The signal represented by expression (3) is then amplitude-limited in such a way that its amplitude becomes constant, and one obtains:

B cos [ω t - \ - ψ (t)] , (4)

where B is a constant. The signal expressed by expression (4), which is thus an amplitude-limited single sideband signal, occupies essentially the same bandwidth as the original telephony signal according to equation (1), its instantaneous frequency

d φ

German

and knowing the expression - ^ - is sufficient to repeat

Uf

production of the useful signal cos [φ (t)].

It is already, for example by the German Patent No. 878,381 is known, the amplitude a (t) of a TeIefoniesignals and its instantaneous frequency - to be transmitted separately, either in separate channels or sequentially in the same channel, the telephony signal is first subjected to frequency conversion - ^ is subjected and takes the form of a single sideband signal. The amplitude is obtained by linear rectification of the converted signal and its instantaneous frequency by limiting and by converting the limited, frequency-modulated oscillation into an amplitude-modulated signal proportional to the instantaneous frequency by means of a frequency modulator (discriminator). However, in the previously known technology, the amplitude and the instantaneous frequency are both transmitted, the telephony signal being restored at the receiving location by frequency modulation of a spatial frequency with the signal representing the instantaneous frequency and by amplitude modulation of the frequency-modulated signal thus obtained. Finally, the frequency of the resulting signal is converted into the voice band again.

According to the invention, the amplitude expression α (t), which is not necessary for speech intelligibility, is not transmitted. It will not damage the eyes either

809 528/329

3 4

eye frequency immediately, but a fraction of the disadvantage, a remainder of the unwanted side viewing transfer. band pass, the level of which is wide, for example in the range of the The invention is based on the knowledge that the level of

the transmission of the instantaneous frequency ^ -necessary _K ^l ™ sideband harbors This remainder is the consequence of the ⁰⁰⁰ ^ - dt ° S difficulty in generating a speech frequency signal that

Bandwidth is much narrower than the bandwidth necessary for transmission over a frequency of cos [φ (t)] compared to a given signal. In other words, the bandwidth of 3500 Hz, phase shifted by exactly 90 °, represents cos [ωt -f- φ (t)] with a very low modulation- is. The aforementioned amplitude limitation brings about frequencies, but with a high degree of modulation, but a further reduction in the amplitude of the unmodulated wave. Io desired sideband.

Accordingly, the signal according to expression (4) becomes. Referring to the drawings, the invention becomes

Frequency division by a factor N subject to their better understanding in further details of which considerable, for example, from the size-described.

Order 100 can be, and one thus obtains a new Fig. 1 shows, partly as a block, partly as a principle resultant Signal whose bandwidth is about z. B. a 15 circuit diagram, the transmitter of the telephony transmission unit hundredths that of the signal according to expression (4). device according to the invention;

The bandwidth of about 3500 Hz, which is used for the over- Figs. 2a and 2b represent the waveform of the signals

Transmission of the language is required per se, is thus according to various points of the transmitter circuit reduced to a bandwidth of about 30 Hz, which is even shown in FIG. 1; can be further reduced. Fig. 3 illustrates a block diagram of a with

The transmitted signal is then of the form: the transmitter of Fig. 1 cooperating receiver;

Fig. 4 shows a further embodiment of the transmitter

B-oos ^{mt + (p {t)} (5) of Figure 1;

N Fig. 5 shows a circuit diagram of the single sideband module

25 lators.

This new signal is an amplitude limited input. In Fig. 1, 1 represents the transmitter input terminal to which

sideband signal, which is an iV times narrower bandwidth the telephony signal according to equation (1) is applied, than the signal according to Expression (4). This signal modulates in the single sideband modulator 2

The method of frequency division has a limit, with carrier suppression a carrier wave of the circle because the bandwidth is not below the 3 ° frequency ω for transmission, which is generated by the oscillator 3. At the output of the modulator 2 necessary for the changes in the instantaneous frequency, this appears in amplitude ΛίΓ j. j x. , j. . ",,., Dm. , and phase modulated signal according to equation (3).

Value, i.e. below the bandwidth of - £ - . _{4 bezeiclmet dunes} AmpHtldenbegrenzer, _a n which

The signal according to expression (4) has phase jumps output that is only modulated with regard to its phase

of π corresponding to the zero amplitudes of the signal α (ί) 35 signal according to equation (4) appears. As above

on. In order to eliminate these phase jumps, the is carried out if this signal has Jm according to equation (4)

According to the invention, the frequency of the signal according to expression (4) has essentially the same bandwidth as the signal according to the invention

doubled, so that the signal equation (1), however, has phase jumps of π .

_ _r _ ",,,"> These phase jumps are made in the frequency doubler

Bcos [2cot + 2φ (ή] (6) ₄₀ 5 eliminated.

at the output of the frequency doubler 5 has a bandwidth that is twice as high as that with an eye frequency divider circuit 6 which causes a frequency eye frequency division by the factor 2 η and a mixing

d φ stage 7, a synchronized oscillator 13 and a

2 ω + 2 ~ -. 45 multiple level 17 includes.

** The output of the frequency doubler 5 is connected to the

Instead of a division of the frequency of the in accordance with first control grid signal 9 of the tube 8 to the mixing stage and the equation (4) by N is then the signal after the output of the multiplier stage 17 to the second control equation (6) grid of a frequency division by 2 N sub 10 of this tube connected. The circuit of the thrown to the same resultant signal corresponding to 5o anode 11 of the tube 8 has a resonance circuit 12, the

Equation (S) to get angular frequency ψ- tuned and attached to the grid

The signal according to equation (5), which covers the entire ^ 2 »°

Message contains, has a constant amplitude and 15 of the tube 14 of the synchronized oscillator 13 can be reinforced in C operation. is coupled. This synchronized oscillator has a

Although the single sideband modulator with carrier sub- 55, "2ω, ur α τ? - * """»",ty; _q

j ..! uv-u- Ai-I -j · the frequency-τ; -very close natural frequency. the

printing can be of any type, is preferably ^u 2 «°

a device is used which has a first modulator. Operation of a synchronized oscillator is e.g. B.

with carrier suppression, which describes a carrier in the article »La methode du signal ana-

the angular frequency ω with the telly to be transmitted; etude de la synchronization dans les oscillateurs

foniesignal s (t) modulated, furthermore a second modulator 60 a amplitude lirnite «, which in the» Annales des Τέΐέ-

• with carrier suppression, which a carrier of the same communications «, Vol. 8, No. 1, January 1953, pp. 1 to 9,

Frequency which, however, is published in relation to the former carrier. The output of the synchronized

the phase is ^{shifted by 90 ö} , with a signal σ (t), the oscillator is on the one hand to a further frequency divider

the opposite to the signal to be transmitted also circuit 6 ', which carries out a frequency division by n',

is shifted by 90 °, in the whole by the latter 65 and on the other hand by means of the switching connection 16 to the

The frequency range occupied is modulated, and the closing input of the multiplier stage 17 is switched on,

borrowed means for coupling the two modulator The multiplier stage 17 works with a multiplier

outputs. These single sideband modulators, which do not have a multiplying factor (2η - 1), their resonance circuit 18 is based on the

Filter for suppressing the unwanted sideband _Tr . , _O 2 »-1 _1. , - ^.

have a very simple structure, but have 70 angular frequency 2 ω - ^ - tuned.

5 6

At the first control grid 9 of the tube 8 appears a for a telephony signal according to equation (1) with a

Signal of the instantaneous frequency bandwidth of 3500 Hz was the bandwidth of the

^ "Transmitted signal according to equation (5) 35 Hz, which band

2 ω + 2 —— width value can be reduced even further.

dt 5 Fig. 2a shows the waveform of the single sideband signal

and at its second control grid 10 a signal according to equation (3) before the amplitude limitation.

Instantaneous frequency Curve 42 represents α (t), curve 43 α (t) cos [ω t + φ (t)]

I da> \ 2n - 1 ^ ^ar ^ ^{ast 'rel eme} curve ^st sinusoidal course of

(2ω + 2 - j- \ . Variable amplitude and variable eye

V ^at I 2 η ₁₀ eye frequency.

In the anode circuit of the same tube, Fig. 2b shows the waveform of the single sideband signal

a signal of the instantaneous frequency after amplitude limitation and frequency division. the

Curve 43 of FIG. 2a is divided with respect to frequency

2 co + 2 - ^un d on that represented by straight lines 44

dt 15 levels, from which curve 45 results. This is

^ _n 'a curve of sinusoidal shape with constant ampli

tude and variable instantaneous frequency. That through

which synchronizes the oscillator 13. the signal represented by curve 45 is given by the power

The frequency divider circuit 6 'differs from amplifier 19 (Fig. 1) in the C mode, the

the frequency divider circuit 6 only through the data 20 straight line 46 the grid voltage anode current characteristic

its switching elements, which with the addition of a line of the tube of the amplifier 19 reproduces. Even though Apostrophes with the same reference numerals as that of the signal to be amplified do not have a constant frequency

Circuit 6 are designated. At the output of the synchroni- hat, the current conduction angle θ of this signal is which

sized oscillator 13 'appears the signal is not dependent on the frequency, constant, off-

",, 2 μ j, / λ 25 taken near the points where the amplitude

B · cos - = B · cos, (5) equals zero. But this results in a negligible

2nn 'N distortion, since the telephony signal is at these points

with N - nn ' set, with an instantaneous frequency being very weak.

The receiver (Fig. 3) comprises one of one

2 1 2 - ω H - ³ ° receiving antenna 21 fed high frequency amplifier

dt dt _ 22, a nn by a factor N = 'operating frequency

o _nn ' ~~ α / quenzverfacher 23, which in the example chosen the

Returns the carrier to the vicinity of 2 MHz, and

and a "" times narrower bandwidth compared to that of a frequency converter 24, which is fed by an oscillator of the signal according to equation (4) with B cos [ω t + φ (t)], so 35 generator 25 with a frequency ω that equal to the length of time when nn 'is the previously set limitation condition of the oscillator 3 of the transmitter. The output of the Fregung is sufficient. quenzumwandlers is connected to a loudspeaker 26,

The narrow bandwidth signal according to equation (5) which reproduces the signal cos [φ {{] \. As can already be pointed out directly in this form by working together, the language becomes understandable and the output of the synchronized oscillator 4 ° is switched while maintaining the sound character of the language of the gate 13 'with a speaking person working in C mode restored. The amplifier 19 are transmitted, which in turn has lost the dynamics of the speech, which feeds the transmission channel, and that with intermediate but without unpleasant influence.
circuit of a transmitting antenna 20, if it is an example. In the embodiment according to FIG

wisely is a wireless connection. Other- ⁴⁵ reference numbers 1, 2, 3 and 4 as well as 6, 6 ', 19 and 20, on the other hand, this signal according to equation (5) can be used as a module of the same electrical devices as in FIG the frequency doubler 5 has been eliminated and transmitted. It should be noted that in the event that the output of the amplitude limiter 4 is a carrier with the signal according to equation (5) is amplitude modulated to the input of a synchronized oscillator 27, switched with regard to the amplitude 5 °. The phase changes of the signal according to the constant of the latter are constantly a degree of modulation of equation (4) around π to the syn-100% can be achieved at the output. chronized oscillator 27 appearing signal without input

With a practically proven transmitter according to the river. The frequency of this signal at the output of the oscil-invention the following values were achieved: at every point in time, the lator 27 is the same as that of on

55 Output of the amplitude limiter 4 existing signal

Signal frequency f = ■ = 2MHz, nals, but in contrast to the latter, has none

2 π phase jumps.

after doubling: According to FIG. 5, the single sideband modulator 2 of the

2 ω Fig. 1 represents, a modulating speech signal is applied

2 f = - = 4 MHz, 60 connected to the input terminals 1 and from there it comes up

⁷¹ the two phase shift circuits 41 and 41 ', which

after division by 2-100 means of the two cascaded over the entire been switched from the modulating signal frequency divider, of which the first one made frequency band phase shifts _φ χ and a factor of 20, the second had a factor of 10: φ ₂ cause against each other by 90 ° differ.

2 f 2 ω ⁵ 5 3 is as in Fig. 1 of the high-frequency oscillator, its

= = 20 kHz. Output to the two further phase shifters 28 and 28 '

2-100 400 π is connected, which is the output from oscillator 3

t% 0 · 1 j τ- ² / j -JJ η. ..1 sent a phase lead or a frequency

The signal of the frequency- ^ was immediately over- 1, .? ., _ACO . _A λ

^ö ^ give 2-100 phase lag by 45 each time. At the exit

wear. 70 of the phase shifter 28, a signal is accordingly obtained

E · cos ω t and at the output of the phase shifter 28 'a signal - E · sin ω t.

29 and 29 'are two modulators with carrier suppression, at their outputs the signals:

E · α (t) cos [φ (ί)] cos ω t
- E · α (t) sin [φ (t)] sin ω t

10

appear.
30 is a coupling circuit which the signal

Ea {t) cos [ω t + φ [ή]

generated. ^χ 5

The two phase shifters 41 and 41 'are identical to each other except for the values of their switching elements, and the Switching elements of the phase shifter 41 'are given the same reference numerals with the addition of an apostrophe referred to as the corresponding switching elements of the a ° Phase shifter 41.

The phase shifter 41 has a tube 40, to the grid of which the modulating signal is placed, and also an anode resistor 33 and a cathode resistor 32 of equal resistance values. This means that the signals appearing at the anode and cathode have the same amplitude but opposite signs. The anode is connected to the cathode via a series circuit consisting of capacitor 34 and ohmic resistor 35 and a parallel circuit consisting of capacitor 36 and ohmic resistor 37. Furthermore, parallel to the parallel circuit 36-37 connected in series with the cathode resistor 32, there is a parallel circuit consisting of a capacitor 38 and an ohmic resistor 39 .

The capacitances of the capacitors 34, 36 and 38 and the values of the resistors 35, 37 and 39 are chosen such that each of the three circuits 34-35, 36-37 and 38-39 has the same time constant τ.

The capacitances of the capacitors 34 ', 36' and 38 ' and the values of the resistors 35' 37 ' and 39' are also chosen such that each of the three circuits 34'-35 ', 36'-37' and 38'-39 'has the same time constant r'.

The calculation of the values of the switching elements 34, 36, 38, 34 ', 36', 38 ', 35, 37, 39, 35', 37 ', 39' should not be carried out here. One finds the same z. B. in the article "Wideband Phase-Shift-Networks" in "Electronics", December 1946.

In the event that the telephony signal extends over a frequency range between 140 and 3500 Hz extends, one can take the following values for the switching elements according to FIG. 5:

• "■ 39 -

3 C ₃₄ .

Q 6

■ ^ 35 '~

R ₃₇ , =

24,000
5 350
4030
892
8 060
1785

= R ₃₃ , = 3000 ohms

• "■ 32 ·

20,000 ohms
120,000 ohms

60,000 ohms
pF
pF
pF
pF
pF
pF

Claims (3)

Patent claims: 1. Device for telephony over a channel with a bandwidth of some 10 ¹ Hz, characterized on the transmitter by a device (2) for modulating a carrier wave with the telephony signal to obtain a single modulated sideband signal without a carrier, through an amplitude limiter (4) for this Single sideband signal and by a device (6, 6 ') for dividing the frequency of the signal limited in amplitude by a given factor, further by means for transmitting the frequency-divided signal to a receiver and at the receiver by a device (23) for Multiplication of the frequency of the received signal by the same factor and by means of a device (24) for mixing the frequency-multiplied signal with a carrier wave of the same frequency as the carrier wave of the transmitter modulator (2), whereby a signal of constant amplitude corresponding to the original telephony signal is obtained. 2. Device according to claim 1, characterized in that the frequency division and multiplication factor is of the order of 100 and the transmitted signal has a bandwidth of Of the order of 30 Hz. 3. Device according to claim 1 or 2, characterized in that the transmitter between the amplitude limiter (4) and the device for dividing the frequency (6, 6 ') a device for multiplication the frequency (5) is provided, which doubles the frequency to the phase jumps of the to eliminate amplitude-limited signal, and that the device (23) for multiplying the frequency at the receiver has a multiplication factor twice smaller than the division factor of the device (6, 6 ') on the transmitter. Considered publications:
German Patent No. 878,381;
"Funk und Ton", 1951, pp. 374 to 376. For this purpose 2 sheets of drawings © »09 528/329 5.58