DE2262939B2 - Circuit for evaluating pulse-modulated alternating voltages, in particular pilot voltages in carrier frequency systems - Google Patents

Description

The invention relates to a circuit for evaluation pulse-modulated alternating voltages, in particular pilot voltages in carrier frequency systems with a the input of the overall circuit forming the rectifier.

Primary group amplifiers in carrier frequency systems are monitored by means of pilot voltages. Included becomes the pilot voltage on the transmitting side of the one Direction of transmission switched on and off (pulse-modulated) in a certain pulse-duty factor, if the Transmission in the other direction is disturbed.

DE-AS 11 33 822 discloses a circuit arrangement for displaying deviations in amplitude an alternating voltage from a setpoint value, in particular for pilot level monitoring in carrier frequency systems, is known. The received alternating voltage, pilot voltage, is rectified. With the Difference between the resulting relaxation and a comparison voltage, a transistor general is driven. The oscillations of the transistor generator are displayed and are a Measure of compliance with the specified setpoint. This procedure is when the pilot voltage is keyed not very suitable because the transistor generator starts to oscillate with a delay and has a hysteresis, i.e. H. the Level values when the vibration is torn off and restarted are not the same.

From DE-AS 12 74 195 a circuit arrangement for the selective reception of a sinusoidal measurement or pilot signal in a carrier frequency system is known. In two receiving channels working in parallel, the pilot signal is modulated with two carrier voltages of equal frequency, shifted in phase by 10 relative to one another, and then rectified in a phase-sensitive manner. The resulting information signal is of frequency deviation zwisc ''^<% n carrier voltage and pilot signal freed This circuit arrangement has the disadvantage that it is responsive to changes in amplitude of the pilot signal, which occur between the ring modulator and evaluation device.

• i The object of the invention is to provide a Specify circuit that supplies a signal in the case of the pilot AC voltage being sampled, in the case of a any other change in the amplitude of the pilot alternating voltage does not emit a signal.

ι ο This task will! solved in that the circuit a first voltage-dividing low-pass filter that has a time constant with a value between the reciprocal values the alternating voltage und.der sampling frequency has a second voltage dividing low-pass filter, its Parting factor is greater than that of the first low pass and the one time constant with a value above the reciprocal values of the alternating voltage and the Has a sampling frequency and contains a differential amplifier, the low-pass outputs each having a differential gain input and the low-pass inputs are connected to the rectifier, which is the input of the Overall circuit forms

A further development has a rectifier with connected smoothing capacitor to the content of is connected to the output of the differential amplifier

The operation of the circuit of the invention will be explained with reference to FIG This is the entrance point E _1, a first, not here shown,

connected upstream in rectifier D 1 DV is the differential amplifier with the non- inverting input Eni and the inverting input Ei; Ri, R 2 and CX form a first low-pass filter; Λ 3, R 4 and C2 form a second low-pass filter.

r> It is

RXIRl <R3 / R4

Cl [Rl \\ R2) <C2 [R3 \\ R4)

Eq. I.
Eq. 2

and with the pilot frequency fp and the sampling frequency ft surrendered

I.
77

Ji

< C2 (R3 || «4)

CiI. .1

Gl. 4th

The pilot voltage in the same direction flies at the point at. It is in the form of half sine waves. This tension is smoothed out by the low-pass filters.

In the steady, steady state, -, -, corresponding to Eq. 1 the DC voltage at Ei is higher than that at Eni; the output of the differential amplifier DV has a negative potential.

Both low-pass filters can follow a slow, steady change in the pilot voltage; the equilibrium voltage on Ei remains higher than on Eni; the output of the differential amplifier remains at negative potential.

When the pilot voltage is sampled as described above, it follows according to Eq. 3 and Eq. 4 the tension at Ei the Taslfreqiicnz much more markers than the h-> tension at Eni; the sign of the output voltage difference changes periodically with the sampling frequency and a square wave is produced at the output of the differential amplifier.

With the help of the voltage divider R 5, P, C3 , this output voltage is rectified and smoothed. When the input AC voltage is not sampled, the capacitor C3 is charged. If the keying starts, the capacitor C3 is periodically fully discharged via the diode D and only slightly charged via the resistor RS; the capacitor remains practically discharged, the output of the circuit is at negative potential,

1 sheet of drawings

Claims (2)

Claims; 1, circuit for evaluating pulse-modulated alternating voltages, in particular pilot voltages in carrier frequency systems with a rectifier forming the input of the overall circuit, characterized in that the circuit has a first voltage-dividing low-pass filter which has a time constant with a value between the reciprocal values of the alternating voltage and the sampling frequency second voltage-dividing low-pass filter, the division factor of which is greater than that of the first low-pass filter and which has a time constant with a value above the reciprocal values of the AC voltage and the sampling frequency and contains a differential amplifier (DV) , the low-pass outputs each having a differential amplifier input and the low-pass inputs together the rectifier ^ s are switched, which forms the input of the overall circuit 2. A circuit according to claim 1, characterized in that a rectifier (R 5, D) with the smoothing capacitor (C3) connected is connected to the output of the differential amplifier (DV)