DE1015501B - Circuit for obtaining a frequency adjustment voltage for receivers to receive frequency-keyed telegraph characters - Google Patents

Description

GERMAN

LIBRARY DESCEUTSCHEN PATENT OFFICE

When receiving frequency-shifted telegraphic transmitters, the receiver has to adjust the frequency necessary so that the frequency inconsistency of the transmitter or the receiver or of both does not interfere.

It has been proposed to convert the symbol frequency and the pause frequency into the same frequency position and to use the voltages of the converted frequency position for frequency adjustment. However, a narrow filter that is tuned to the common frequency position is necessary, which means associated with a number of disadvantages.

Behind the limiters that are usually used, there is, in particular, a small signal-to-noise ratio at the receiver input the message is frequency-modulated by the noise. The aforementioned procedure in which the symbol and pause frequency is converted into the same frequency position, works with a small signal-to-noise ratio and if the filter is narrow compared to the hub, no more, although the telegraphic characters are still can be evaluated. If stations with different hubs are to be received, the bandwidth of the Filters are sized according to the smallest stroke, d. i.e., the filter (provided that it is in the Bandwidth is not adjustable) is relatively narrow in most cases, so that the known circuit at must fail with a small signal-to-noise ratio.

To set a frequency adjustment voltage for radio receivers to receive frequency shift keyed To obtain telegraphic characters, one needs to be of the same kind for both the pause frequency and the key frequency Control DC voltages. These can then be achieved when in the curve showing the dependency the control voltage of the frequency is concerned, the same working edge for each of the shift frequencies occurs.

For this purpose, circuits are known in which several resonance circuits are connected together will. In doing so, however, there are considerable difficulties in finding the branches of the different resonance curves to be merged into one another with a smooth course and to achieve good symmetry of the combined parts. The inequalities in the curves mentioned above and the coordinate axis, which can hardly be avoided enclosed areas are particularly of great disadvantage when it is small Signal-to-noise ratio is. The acquisition of an accurate frequency adjustment voltage is known from the Arrangements made difficult by the fact that the zero crossings as a result of the superposition of the resonance curves are very blurred.

The invention, which comprises a circuit for obtaining a frequency adjustment voltage for radio receivers for the reception of frequency-shifted telegraph characters, whereby the

Circuit for extraction
a frequency adjustment voltage

for recipients

for receiving frequency-keyed
Telegraph sign

Applicant:
Siemens & Halske Aktiengesellschaft,

Berlin and Munich,
Munich 2, Wittelsbacherplatz 2

Dipl.-Ing. Dieter Leypold

and Dipl.-Ing. Werner Poschenrieder, Munich,
have been named as inventors

Grenzer conducted IF voltage by means of a hybrid circuit once directly and once via a phase shift element a phase bridge is fed, which the control voltage for performing a frequency adjustment supplies, avoids the difficulties mentioned in that the phase shift member at least has such a large linear frequency response that they are used for frequency shift keying Frequencies each result in a working curve running in the same sense.

It is known to obtain a frequency adjustment voltage when receiving frequency-modulated transmissions, the intermediate frequency voltage once directly and once via a phase shift element to a phase bridge, which supplies the control voltage. In these known circuits however, only a single working edge is required.

The invention, however, is concerned with the reception of frequency-shift keyed telegraphic characters and shows a way to use a new and advantageous design of the phase shift member several in the same To create meaningful working flanks.

For the reception of single-frequency-shift keyed transmitters, according to the invention, the phase shift element should have a linear frequency response of at least π / 2 to 9 π / 2 , the steepness of the phase rotation between the two f ^ frequencies the phase difference

renz results in 2π and the phase shift in the F ₁ -FrC- frequencies is 3 / 2π and 7 / 2π.

For the reception of duoplex transmitters, the phase shift element according to the invention has a linear frequency response of at least π / 2 to Π π / 2, where

-0Ϊ686 / 225

the steepness of the phase rotation between the four telegraph frequencies results in the phase difference 2π and the phase rotation at the four frequencies is 3 / 2π, 7Ι2π, \\ Ι2π and 15 / 2π.

The invention also provides the possibility that the phase shift element can be switched over in stages.

In the event that a Fj receiver is to be used either for receiving A ₁ , A ₂ or - ^ ₃ transmitters, the polarity of the frequency adjustment voltage must be reversed.

In Fig. 1, the circuit according to the invention is shown in principle. The intermediate frequency voltage passed through a limiter is fed to a phase bridge M once directly via the fork g and once via a phase rotating member .S. This phase shift element is dimensioned so that its phase curve ψ corresponds to the curve of FIG. 2, that is to say that a linear phase curve of π / 2 to 9 π / 2 is present. Under this condition, a DC control voltage U _T is obtained at the output of the phase bridge AI , the course of which is shown in FIG. 3 as a function of the frequency F. If the phase shifting element is correctly dimensioned according to the frequency deviation of the telegraph _{transmitter to be received, the J7 r} curve runs at frequencies F ₁ (e.g. pause frequency) and F ₂ (e.g. crossover frequency) both times with increasing frequency from bottom to top. At the frequencies F ₁ and F _{2, there} is no adjustment voltage U ₁ at the output of the phase bridge M. Here the phases of the two voltages on the phase bridge are just 90 ° shifted from one another. This means that the phase shifter has rotated the phase by 3 / 2π or 7Ι2π. It is of course possible to use an even longer straight curve. However, this increases the effort and is of no advantage. The specified dimensioning represents the minimum effort.

If the receiver is detuned, both frequencies will shift up or down. The same type of control DC voltages result from both frequencies. If the characters are frequency-modulated by noise, an additional noise AC voltage is generated at the output of the phase bridge which is superimposed on the direct current and which can be filtered away using known means as required. With correct coordination, ie with the position of F ₁ and F ₂ according to FIGS. 2 and 3, an alternating voltage is produced, the mean value of which is equal to zero, so the frequency adjustment does not respond. If the receiver is detuned, the resulting value of the control voltage is changed (slightly reduced) by the noise, but the sign of the control voltage is retained so that the adjustment device can work correctly even under these conditions. The prerequisite for this is that the curves run exactly symmetrically from points F ₁ and F ₂ until the zero line is reached again. So-called all-pass filters are expediently used as phase rotators; these are bridge circuits with constant wave impedance Z, in which the bridge reactances χ and y meet the condition

Z ² x = - suffice, ie are reciprocal. As an example

a so-called ß-member is given. A link of this type rotates the phase between the frequencies 0 and σο by the angle 2 π. The π passage of the phase is determined by the frequency F ₀ . Any number of phases can be achieved by connecting several links in a chain or by using complex bridge reactances. If you replace the reactance χ or y with an ohmic resistance Z = \ 'xy', you get a phase shift element that has a constant basic attenuation of 0.7 N, but with the same phase profile only requires half the cost of coils and capacitors. The known conversion into a differential T-circuit finally results in the circuit of the phase shifting element indicated in FIG. 4, which has the advantage of a particularly low cost of components. The requirement for a linear phase profile results in an equidistant distribution of the zero and pole positions of the bridge reactance (see also Guellemin, Communication Networks, Vol. II).

If the above-mentioned condition (curves symmetrically from the values -F ₁ and F ₂ ) is not fulfilled, a direct current component is created in the case of strong noise, which leads to incorrect regulation of the frequency adjustment. The condition is met when the phase rotation of the phase shift member is largely linear Γ at least from π / 2 to 9 π / 2

In the arrangement according to Fig. 4, the IF voltage passed through a limiter is fed to the terminals 1 and 2 of a transformer 3, the secondary side of which is formed as a hybrid circuit and once directly with the control grid of an amplifier tube 4 and once via the phase shift element 5 ¹ with a Amplifier tube 5 is connected. As mentioned above, the phase shifter S is designed as a differential T circuit, the resonant circuit assembly of which is formed from the inductors 6, 7, 8 and the capacitors 9, 10, 11 and 12. This resonant circuit assembly is connected in the electrical center of a series inductance 13. The anodes of the amplifier tubes 4 and 5 are connected via the transformers 14 and 15 to a ring modulator 15 designed as a phase bridge, which is constructed in a known manner from rectifiers 18, 19, 20 and 21 and cfen resistors 22, 23, 24 and 25. The DC control voltage for performing the frequency adjustment is taken from terminals 26 and 27, which are each connected to the middle of the secondary side of the transformers 14 and 15.

If transmitters with frequency deviations of different sizes are to be received, the steepness of the phase rotation must be adapted to the respective deviation. The pivot point is the frequency F ₀ , at which there must always be a 5 / 2π phase shift. An exact correspondence of the zero crossings 3/2 π and 7/2 π with the telegraph frequencies is not necessary. If this correspondence is not completely present, an alternating voltage corresponding to the telegraphic characters is superimposed on the output direct voltage, which does not interfere.

The CCI has proposed a series of standards for frequency swings in frequency-keyed shortwave transmitters, which have an equal progression of about 30 ⁰ Io. It is sufficient if the steepness of the phase shift is changed in equal steps jj & fenn. Any fluctuations in between can then be received without further ado. To change the slope, it is advisable to switch the entire resonant circuit assembly. If the transmitter travel is unknown, the correct phase setting can be found by observing the magnitude of the output AC voltage of the phase bridge for large strokes (smallest steepness) after a smaller stroke, then the correct setting is reached when the alternating voltage has a minimum for the first time. · .. '. "

With A ₁ -, A ₂ - or ^ -operation the carrier is bet F ₀ in Fig. 2. If the polarity of the frequency control voltage is reversed,

so you can use the circuit according to the invention for obtaining a frequency adjustment voltage in these operating modes also use.

The circuit according to the invention for obtaining a frequency adjustment voltage can also be used for duoplex operation, with four frequencies being transmitted alternately at the same frequency spacing from one another. In this case, the linear phase response of the phase shift member S in Fig. 1 must be lengthened accordingly.

As explained above, FIGS. 2 and 3 show the phase curve and the control voltage as a function of the frequency F for simple frequency shift keying with the frequencies -F ₁ and F ₂ . The corresponding representations for duoplex operation with the four frequencies F ₁ , F ₂ , F ₃ and F _{4 are} shown in FIGS. 5 and 6. FIG.

If a correspondingly dimensioned phase shift element is used for duoplex operation, the circuit according to the invention can be used either for duoplex operation or for simple frequency shift keying, provided that the frequencies either at F ₁ and F _i or at F ₂ and F ₃ (Fig. 5 ) lie.

Claims (4)

Patent claims: 1. Circuit for obtaining a frequency adjustment voltage for radio receivers for reception of frequency-keyed telegraph characters, whereby the IF voltage passed through a limiter by means of a hybrid circuit once directly and once via a phase shift element of a phase bridge is supplied, which is the control voltage for performing a frequency adjustment supplies, characterized in that the phase shift member at least one linear Frequency response has that there is one for each of the frequencies used in frequency shift keying results in a working curve running in the same sense. 2. A circuit according to claim 1, characterized in that for the reception of single frequency shift keyed transmitters the phase shift element has a linear frequency response of at least π / 2 to 9 π / 2 , that the steepness of the phase rotation between the two Fj frequencies results in the phase difference 2 π and that the phase shift at the Fj frequencies is 3/2 π and 7/2 π, respectively. 3. A circuit according to claim 1, characterized in that for the reception of duoplex transmitters, the phase rotation element has a linear frequency response of at least π / 2 to 17 π / 2 , that the steepness of the phase rotation between the four TeIegrafiefrequenzen results in each case the phase difference 2π and that the Phase rotation at the four frequencies is 3/2 π, 7/2 π, 11/2 π and 15/2 π. 4. Circuit according to one of the preceding claims, characterized in that the Phasers can be switched in stages. Considered publications:
German Patent No. 635 535;
British Patent No. 448,448;
U.S. Patent Nos. 2,354,827, 2,423,229. 1 sheet of drawings © 709 695/226 9 '.