DE1050801B - Circuit arrangement for the optional demodulation of two radio teletype channels combined by multiple frequency shift keying - Google Patents

Description

GERMAN

In the case of the multi-frequency shift keyed radio teletyping systems (Twinplex), it is known that two Telegraph channels grouped together to form a single channel on the frequency scale. Correspond the character and separating position of the individual telegraphing steps on both channels is each one emitted by four keying frequencies symmetrically to the center frequency of the transmitter. Each of these frequencies is clearly assigned to a single state of one and the other message, thus represents one of the four possible character tiOm-T rennstrom-Combination. There are several possibilities, the keying frequencies certain Assign identification states (character or separator stream). Internationally one has to rely on the two agreed the following codes:

Code 1

Channel A TTZZ
Channel B ZT TZ

fifijzfi

ro

Code 2

Channel A TT ZZ

Channel B TZTZ

fifz UU

ίο

While demodulation with a discriminator does not cause any problems with the Α-channel, since below the center frequency (/ ₀ ) there are only separating current criteria (T) and above the center frequency (Z ₀ ) only character stream criteria (Z), this method can be used with the B. -Channel not run because here both sides of the center frequency (/ ") both separating current and character stream criteria occur.

The known arrangements for demodulating both channels are therefore all used for each channel different facilities because the demodulation of the Α channel is very easy, the demodulation of the B-channel, on the other hand, is relatively difficult to carry out.

For demodulating the Α channel, it is known, in addition to the common discriminator arrangements, to feed the keying frequencies on the one hand via a series resonant circuit tuned to the center frequency and on the other hand directly to the inputs of a push-pull modulator. Compared to the reference voltage fed directly to the first input of the push-pull modulator, the voltage tapped between L and C of the series resonant circuit has in-phase or antiphase, depending on whether it is above or below the center frequency, which then results in character current or separating current steps in a known manner via the push-pull modulator .

For the demodulation of the B-channel, a method is known that involves a complex interconnection arrangement

optionally demodulation

two radio teletype channels combined by multiple frequency shift keying

Applicant:

German Federal Post Office,

represented by the President

the Central Telecommunications Office,

Darmstadt, Rheinstrasse 100

Kurt Reubold, Frankfurt / M.,
has been named as the inventor

Storage, frequency swapping and filtering out of the keying frequencies work to achieve the required assignment to achieve the character and separation current criteria for the individual keying frequencies.

It is also already known to demodulate the B channel with the connection of two networks to achieve in which the phase angle difference of the alternating voltages supplied to the push-pull demodulator is an integer multiple of 180 ° and differs from the adjacent keying frequency in each case differs by 180 °.

Around the quadrupole made up of reactive resistances when using phase-shifting To reduce the resulting settling times, it is also known before the four-pole ohmic resistors to switch.

The invention is also based on a network that has an isolating current criterion between each assigned keying frequency and the next keying frequency assigned to a character stream criterion each has a phase jump of approximately 180 °. Compared to all known embodiments However, it solves the problem of the optional demodulation of both the A and the B channel with one incomparably less effort through a single network. It is based on the knowledge that a series connection a parallel resonance circuit with a series resonance circuit with appropriately chosen Resonance frequencies already has the phase response that is necessary for demodulating the B channel corresponds and which can be achieved by simple transposition

809750/206

a tap on the series circuit can be adapted to both codes. It is used to demodulate the Α channel then only necessary to short-circuit the parallel resonant circuit and do the demodulation in the manner described above known way. As a result, the object of the invention can be achieved with a single Network to be able to demodulate both the A and the B channel, very easily solve. The invention is therefore characterized in that

gene phase. The result is one that corresponds to the characteristic states of code 2 / of the B-channel Phase order.

This consideration applies in a similar way to the other exemplary embodiments in FIG. 3; For code 1 of the B channel, there are initially two identical characteristic states symmetrical to the center frequency, so that here only the transition from f _± to / ₂ and from / 3 to

keying frequency assigned to a separating current criterion and the next, a character current criterion assigned switching frequency in each case a phase jump of 180 °. Such a network is sufficient thus inherently the requirements for the phase curve, as they are with the two codes of the B-channel appear.

The mode of operation of a built with the network according to the invention. Demodulation arrangement

that the phase-shifting network from the rear 10 will be shown below with reference to Fig. 2 and z. B. other circuit of a parallel resonance circuit with the Fig. 3, c for the code 2 of the B-channel explained a series resonance circuit consists of one.

corresponding to the channel to be demodulated and / or The phase position of the reference voltage U ₁ in relation to the am

Code changeable tap on the voltage U ₂ tapped one behind the other is determined by the circuit of a voltage (U ₂ ) supplied to one input of the push-pull modulus ratio of the total impedance to the lator with a partial resistance tapped off the Zei. The particle flow or separation flow criterion clearly characteristic resistance in Fig. 3, c consists of a capacitance-drawing phase position compared to that of the other. According to Fig. 2, the total impedance input of the push-pull modulator is capacitive for the sampling frequency I ₁ = 2.1 kHz, bypassing the reference voltage (U ₁ ) supplied in the Verdes network in relation to the partial resistance, which is always capacitive. So there is phase equality. At the next turn

As measurements have shown, there are concerns of scanning frequency / ₂ = 2.5 kHz is the total emitter side because of the fact that the telegraph speed drops in the stand inductive (see Fig. 2) - partial resistance is therefore antiphase , at which the settling time of the network is not right, 25 keying frequency / ₃ = 2.9 kHz, again the same could be done with a network according to the invention phasing, at the keying frequency f _i = 3.3 kHz even step speeds of 200 baud safe ~ ~

to process.

As experiments have shown, if the keying of code 2 is not synchronized, you can use the previous one Demodulation method omit the necessary phase folder on the transmission side without As with the known methods, the number of errors increases for the same signal-to-noise ratio. This benefit will

a phase jump is necessary in each case due to the excessive voltage at the resonance 35. The adjustment points of the network conditional; There is therefore a solution to the various codes in the execution high demodulation ratio (ratio of the examples achieved simply by taking the output voltage to the input voltage). touched the entire series oscillation circuit once

In the following, several figures (code 1), on the other hand only on the last blind formations Embodiments of the invention is 40 resistance of the series resonant circuit (code 2). give. . For demodulating code 1 of the B channel

Fig. 1 shows the network according to the invention; the results shown in Fig. 3, α and b

Fig. 2 shows the impedance curve and the options that are only available through the Phase response of an embodiment of the network according to the invention;

Fig. 3 shows in four representations α to d the options for demodulating code 1 and code 2 in the B-channel;

Finally, Fig. 4 shows the switching arrangements carried out, each of which enables demodulation of the 5 ° phase position of the voltage Α-channel tapped on the network and of both codes of the B-channel by corresponding U ₂ compared to the reference voltage U ₁ in the case of the individual switching.

Fig. 1 shows the series connection of a series resonant circuit with a parallel resonant circuit according to the invention. This arrangement has a parallel resonance and two series resonances, which are above and below the 'parallel resonance. The parallel resonance is formed by L ₂ and C ₂ , while the series resonance is formed by all reactances

are formed. The series circuit L ₁ , C ₁ has the same resonance frequency again Α-channel and both codes of the B-channel show parallel circuit L ₂ , C ₂ , because it is then also very simple allows the low-frequency output voltage of the Empeine to perform demodulation of the Α-channel. If you make the parallel resonance equal to the middle connection of the parallel resonance circuit with the series frequency and feed the series resonances into the connected resonance circuit. The voltage U ₁ serves as permanent frequency gaps, so that results in the reference voltage, it goes directly to the input of Fig. 2 shown phase and apparent impedance of the limiter amplifier BV ₁ . The voltage U ₂ becomes the state curve. on the other hand at an outlet corresponding to the operating mode

As can be seen from the phase curve in Fig. 2, the network handle is removed and the network according to the invention is fed to the second between each 70 limiter amplifiers BV _2. The ones in the

Differentiate the polarity of the resulting voltages. For the demodulation of code 2, the tap on the series connection of the two circuits must be laid between the inductance and capacitance of the series circuit, as Fig. 3, c and d show. Below Fig. 3, α to d is in each case the

NEN to key frequencies specified. A plus sign is said to be in phase, a minus sign to be opposite in phase imply.

The voltages U ₁ and U ₂ are each fed to a limiter amplifier BV ₁ and SF ₂ before they act on the push-pull modulator, as can be seen in detail in FIG.

In the two circuits of Fig. 4, which again-

Fig. 3, ο to d specified different tapping points for the two codes of the B-channel are reached by a switch. For the demodulation of the Α channel, the parallel circuit is short-circuited with the switch in the / switch position; the arrangement for demodulating the Α-channel already mentioned in the illustration of the prior art is then present. With the arrangements shown in Fig. 4, a and b , on the one hand the Α-channel and on the other hand the two codes of the B-channel can be demodulated with the same network by simple switching.

The direct current signals coming from the push-pull modulator GM are supplied in a known manner to the receiving relay ER in all embodiments, which causes the relay.

Claims (6)

Patent claims: 1.Circuit arrangement for the optional demodulation of two radio teletype channels combined by multiple frequency shift keying (Twinplex), in particular the channel in which both character stream and separation current criteria are located on both sides of the center frequency (B channel), through a network connected between the receiver output and a push-pull modulator, which has a phase jump of approximately 180 ° between each keying frequency assigned to a separating current criterion and the next keying frequency assigned to a character current criterion, characterized in that this network consists of the series connection of a parallel resonant circuit with a series resonant circuit, one corresponding to the channel to be demodulated and / or Code changeable tap on the series connection a voltage (f / ₂ ) fed to one input of the push-pull modulator with a phase la uniquely identifying the character current or separating current criterion ge compared to the reference voltage (U ₁ ) supplied to the other input of the push-pull modulator, bypassing the network. 2. Circuit arrangement according to claim 1, characterized in that the network has three resonance frequencies having, the parallel resonance to the center frequency and the two series resonances be placed symmetrically on both sides of the center frequency according to the stroke. 3. Circuit arrangement according to claim 1, characterized in that the parallel resonant circuit and the series resonant circuit can be tuned to the center frequency. 4. Circuit arrangement according to claim 1 and 3, characterized in that when the Α channel is received, the parallel resonance circuit is short-circuited and the _{voltage to be supplied to the second input ([Z 2} ) of the push-pull demodulator is tapped between the inductance and the capacitance of the series resonance circuit. 5. Circuit arrangement according to claim 1, characterized in that for the demodulation of code 1 of the B channel, the tap is placed between the series and parallel resonance circuits. 6. Circuit arrangement according to claim 1, characterized in that for the demodulation of code 2 of the B channel, the tap between the inductance and the capacitance of the series resonant circuit is placed. 1 sheet of drawings © 809 750/206 2.59