DE810521C - Mixed detector circuit - Google Patents

Description

The present invention relates to a mixer detector circuit for demodulating frequency modulated Vibrations in which the frequency-modulated vibrations to be demodulated demodulated one of two circuits coupled to one another can be fed to the two circuits phase-shifted vibrations generated are fed to two control grids of a mixing tube. If the phase shift between the

ίο vibrations from both control grids the frequency of the supplied vibrations depends, the anode current of the mixer tube contains a Low-frequency component, which is in a first approximation proportional to the frequency deviation of the one to be demodulated Vibrations is.

The coupled circles from which the two phase-shifted oscillations are taken must be form a network that fulfills the following conditions: 1. The phase shift between the two output voltages must be approximately for the mean frequency of the oscillations to be demodulated Be 90 °; 2. The phase difference must also be proportional to the largest frequency deviation be the frequency deviation; 3. the proportionality factor

as between this phase shift and the frequency deviation must be as large as possible; 4. the one representing the phase shift as a function of the frequency The characteristic curve must be horizontal for frequency swings that exceed the highest frequency swings that occur get lost.

The first condition ensures a symmetrical working curve.

The fulfillment of the second condition results in distortion-free demodulation; becomes the third condition is met, there is great sensitivity. The fourth condition brings about that peaks cut off in the transmitted signal. This condition does not include one on the middle frequency corresponding working characteristic for large frequency swings from coordinated circles; in this case peak voltages in the signal to be transmitted would lead to very large distortions of the demodulated Signal.

A circuit with two coupled circuits satisfies the first, third and fourth of those mentioned above Conditions, but the linearity is insufficient for large frequency swings.

The invention aims to provide a circuit which satisfies all of the above mentioned requirements and which is very cheap to build.

According to the invention, a third circuit is coupled to the second of the two coupled circuits, which is matched to the mean frequency of the vibrations to be demodulated. The coupling and the attenuation of this third circle can be dimensioned in such a way that there is better linearity results.

The invention is explained in more detail with reference to the embodiment shown in the figure.

In the mixer detector circuit shown in the figure, the vibrations to be demodulated are fed via line 1 to a network 2 which contains the two coupled circuits 3 and 4, at which two voltages are generated which are fed to the two control grids 5 and 6 of a mixing tube 7 will. Both circles are tuned to the mean frequency of the vibrations to be demodulated and coupled such that the phase difference between the voltage on the grid 5 and the on the grid 6 for the mean frequency is 90 °. In this case, the anode current of the tube contains 7 a low-frequency component, which is the first approximation of the frequency deviation of the Vibration is proportional. For large frequency swings, however, the deviation from linearity is impermissibly large. According to the invention, the circle 8 is provided to eliminate this error, the coupled to the circuit 4 and also matched to the mean frequency of the vibrations to be demodulated is.

It turns out that the smallest deviation in the linearity results when the formula D ₃₂ = a -K ₃₂ + b is fulfilled, in the

V δ 2 r ₂ ω ₀ L ₂

is the quotient of the damping factor of the third circle by that of the second circle and

^ ₃₂ - -

'2

where α is a constant between the values 1.5 and 2.5, b is a constant between the values 0.2 and 0.3, W _{0 is} the mean frequency of the vibrations to be demodulated, Af _{32 is} the coupling between the third and the second Circle, r _{2 is} the loss resistance of the second, j / J "that of the third circle.

Claims (2)

PATENT CLAIMS: 1. Mixing detector circuit for demodulating frequency-modulated oscillations with two coupled Circles, the first of which are supplied with the vibrations to be demodulated and at the phase-shifted vibrations generated on the two circles two control grids are fed to a mixing tube, characterized in that with the second of the above mentioned coupled circuits a third circuit, which is based on the middle frequency of the to be demodulated Vibrations is matched, is coupled in such a way that the linear control range is increased will. 2. Mixing detector circuit according to claim 1, characterized in that the coupling of the second and third circles and the attenuation of the third circle are dimensioned such that the formula D ₃₂ = a ■ K ₃₂ + b is fulfilled.