DE832306C - Mixing detector circuit for demodulating frequency-modulated oscillations - Google Patents

Description

(WiGBl. P. 175)

ISSUED FEBRUARY 21, 1952

ρ 20754 Villa / 21 a * D

has been named as the inventor

In a known mixer detector circuit for demodulating frequency-modulated oscillations the vibrations to be demodulated are fed to two coupled circuits, of which the second is tuned to the center frequency of these oscillations, with the over the two circles generated voltages, which depends on the frequencies of the vibrations to be detected Have phase shift, two control grids are fed to a mixer tube, so that a current with a low frequency component flows in the anode circuit of this tube, its instantaneous value is proportional to the frequency deviation of the supplied oscillation in a first approximation.

The invention aims to provide a mixer detector circuit based on a different principle create, which also contains a tube with two control grids. It has the advantage that you can get by with simpler switching elements (namely do not necessarily need two coupled circuits to be used) and the sensitivity and linearity are high requirements correspond.

According to the invention, in a mixing detector circuit containing a tube with at least two control grids, the vibrations to be demodulated are fed to the first of the two control grids, this grating operating in AB or β mode. By means of a delay network, a pulsating voltage is taken from another electrode of the same tube and / or an auxiliary tube, which is the

second control grid is supplied in such a way that a constant time after the first grid has become conductive, the second grid operating in the B or C mode also becomes conductive.

The invention is based on the embodiment shown in the drawing (Fig. Ι and ι a) explained in more detail.

The tube shown in the figure contains ι

ίο two control grids 2 and 3, of which the vibrations to be demodulated are fed to the control grid 2 via the line 4. Seen from the cathode, a screen grille (suction grille) 5 is provided in front of the control grid 2, which carries an almost constant current as long as the control grid 2, which operates in AB or 5 mode, does not let any current through. As soon as the control grid 2 becomes current-permeable, the current flowing to the grid 5 decreases rapidly and reaches a certain end value, so that the voltage on this grid increases and assumes a pulse-shaped form. The pulsating voltage generated at the grid 5 is fed via a delay network 6 to the second control grid 3 of the tube 1, which operates in B or C mode. The mode of operation of the circuit is explained in more detail with reference to FIG.

In this figure, the voltage on the grid 2 is denoted by α. At the time b , this grid becomes current-permeable, so that the current flowing to the grid 5, which is indicated by the curve i , decrease rapidly and reach a final value; will achieve. A pulsating voltage is therefore generated on this grid. This pulsating voltage reaches the second control grid 3 of the tube 1 a time t later. The grid 3 is therefore also allowed to pass current at time c. Anode current therefore only flows in the tube 1 between times c and d. As can be seen from the figure, the time cd has a linear relationship to the oscillation time of the oscillations to be detected. It can be seen from the figure that when the time t has a value which is slightly less than half of the shortest instantaneous Oscillation time of the frequency-modulated input signal, the anode current of the tube 1 has a modulation depth of almost 100%. A high sensitivity can therefore be achieved by including a sufficiently high resistance in the anode circuit of the tube 1. The invention is not limited to the embodiment shown in the figure In particular, it is possible to take the pulsating voltage to be supplied to the grid 3 of the tube 1, for example from the anode circuit of an auxiliary tube, whose control grid, which works in AB or B mode, is supplied with the vibrations to be demodulated.

According to a further solution, a pulsating voltage is taken from a screen grid following the grid 2 of the tube 1, which is fed to a phase reversal tube or a transformer, whereupon the phase reversed voltage opens the grid 3 of the tube 1 after a constant time t, this point in time being later than the point in time at which the grid 2 of the tube 1 becomes current-permeable.

Claims (3)

PATENT CLAIMS: 1. A circuit for demodulating frequency-modulated vibrations with a tube acting as a mixing detector with at least two control grids, the first control grid operating in AB or 5-mode, the vibrations to be demodulated are supplied, characterized in that another electrode and / or by means of a delay network an auxiliary tube a pulsating voltage is taken, which is fed to the second control grid, in such a way that a constant time after the first grid has become current-permeable, the second control grid operating in B or C mode also allows current to pass, and that the demodulated vibrations can be taken from the anode circuit of the tube. 2. Circuit according to claim 1, characterized in that that the time delay go achieved by means of the phase delay network is somewhat shorter than half of the shortest as a result of the modulation occurring period of the frequency-modulated input signal. 3. A circuit according to claim 1 or 2, in which the tube successively contains at least one cathode, a screen grid (suction grid), a control grid, a second screen grid, a second control grid and an anode and the first control grid in AB or 5 mode and the second control grid operates in B or C mode, characterized in that a pulsating voltage is taken from the first screen grid (suction grid) via a delay network and is fed to the second control grid. Referred publications:
U.S. Patent N>. 2273771. 1 sheet of drawings 3234 2.