SU445173A1 - Device for detecting dual frequency wired signals - Google Patents

Description

The invention can be used in various radio devices. Quartz or LC discriminators, consisting of four filters, detectors and an interpretation circuit, are used to receive two-frequency telegraphy signals. Such devices have large dimensions and, due to their narrow bandwidth, introduce significant telegraph distortions and impair noise immunity, especially with small manipulation indexes. It is also known a device consisting of two delay elements, a phase shifter and two multipliers, as well as a device with three delay elements, one of which must have a nonlinear phase characteristic. The first device significantly degrades the noise immunity of the reception, since the code frequencies (A / 2, / 3, / 4) of channel I are located at the level of 0.7 of the maximum output voltage; the second device cannot be made universal for any frequency shifts and its dimensions are reduced, since an element with a nonlinear phase characteristic is made in the form of a filter with quartz resonators. The purpose of the invention is to improve the noise immunity of the device for detecting DChT signals. In the proposed device, this is achieved using three delay elements with linear phase characteristics, which can be performed on shift registers or pa quartz resonators. FIG. 1 shows the scheme of the proposed device; in fig. 2 - characteristics. The PST signal is fed to the input of the delay element 1 and the phase shifter 2. The signals from the output of the delay element 3 and the phase shifter 2 are multiplied together. The characteristic for direct current at the output of the multiplier 4 corresponds to the one necessary for receiving signals of DChT via channel II (Fig. 2, d). When the signals are multiplied from the phase shifter 2 and the delay element 1, the characteristic shown in FIG. 2, a, with a phase shifter 2 and a delay element 5 through a resistor 6 — the characteristic shown in FIG. 2, b. If, on the multiplier 7, the sum of the voltages is supplied from the delay element 1 and the resistor 6, the characteristic shown in FIG. 2, c, is necessary to receive DFC signals over channel 1. Since the code frequencies lie near the maxima of the characteristic, the reception noise immunity is high. Resistor 6 serves to select the optimum voltage ratio between delay elements 1 and 5. Delay elements can be

executed on shift registers. The delay time of each of the delay elements is selected from the condition

 one

4D / ADD

where a / sdz - the shift between

code frequencies.

The number of register bits is determined from the condition "/ m-t (where / t is the clock frequency); fT (3-5) fc (where fc is the signal frequency).

Multipliers can be differentially executed. or operational amplifiers or conventional ring mixers.

four

Subject invention

A device for detecting dual frequency telegraph signals containing successively connected delay elements, the outputs of which are connected to non-multipliers, and an input phase shifter, characterized in that, in order to improve noise immunity, the output of the phase shifter is connected to the inputs of the multipliers, the second inputs of which are connected the second mentioned delay elements, and the output of the third delay element is connected to the output of the first delay element through a resistor.

Channel output channel output

and mcayila