SU42607A1 - Device for balanced modulation - Google Patents

Description

As is well known, the modulation of high-frequency oscillations by low-frequency oscillations can be obtained in two ways: by using the non-linearity of one of the cathode lamp characteristics (non-linear modulation) and by using an exclusively linear portion of the characteristic whose slope varies with the modulating frequency and is a linear function of amplitude. last (linear modulation).

The present invention relates to the second of the mentioned methods and is a device for linear balanced modulation in which two shielded lamps are applied, to the control grids of which high-frequency oscillations are synchronously applied to control grids, and the modulating-frequency oscillations to opposite shielding grids.

In FIG. 1 and 2 depict a family of characteristics of a shielded lamp; FIG. 3-modulation characteristic; FIG. 4 is a circuit diagram of the electrical connections of the modulation device; FIG. 5-modified scheme of the device.

(344)

The steepness of the characteristics of a shielded lamp depends, as is well known, on the potential applied to the screen grid. FIG. 2 shows the change in steepness characteristics

(

depending on V .. Approximately this dependence is shown in the form of a straight line, in fact, from above and below it has bends like a curve

/ En-/(.) If the Asiniat high-frequency voltage is applied to the control grid of the shielded lamp, and the low-frequency voltage 5sinQ is applied to the screen grid under some constant positive potential Y, then for the anode current you can write:

Ac sin t - {- 5.5 sin o /,

slope

A .- / () slope

/ "- L (T;).

in accordance with the foregoing and depicted in FIG. 1 and 2 characteristics

/ (,

Where

and tg ",

- - The slope of the curve in FIG. 2. Since V In sin Q i,

and the screen grid is under some initial positive voltage Fgo, which corresponds to the initial steepness of the characteristic

four--/(.)

equal to SQ then

5o {1 - / CsiuQ),

Au

where / С is the coefficient of modulation of the slope equal to

with s

- "th -o

From here

4 - L5o {1 I- / C sin Q b) sin w if -f- | -5, 5 sin Q.

Term

L5o {1-Ь / з1п (5г) sino)

is a modulated high frequency.

The advantages of this method are that the anode current is free from high-frequency harmonics; all the distortions at low frequency due to operation in the straight-line segment are absent.

Transition from idealized characteristics to real ones, it can be said that when choosing a mode that corresponds to the use of only a straight line section of the characteristic

(P)

-5 ,,. / (CL

The above findings will occur.

In this case, the linear modulation depth is normally in the order of 70-80%. However, even with a greater depth of modulation, the distortions will be much less than the distortions inherent in conventional modulation (non-linear). I If in the preceding conclusions po1 lie

 .

i where the letter t denotes the constant i coefficient, the sign at which changes along with the sign К „, i.e. such; coefficient at which

,, - g / gV sin i t,

 . when changing the sign when sin is on: the opposite sign doesn’t change, then

/: tB sin j t sin with S sin t,

T. e. in the anode circuit, there will be only the total and difference frequencies (w-j-u and σ-li), the amplitude of which varies in proportion to the amplitude of the modulating frequency. The carrier frequency (a) at any value of B will be absent.

The coefficient t. Can be attributed to the specified property of a sign change, if the characteristic

5, c - / (Q

will have the form shown in FIG. 3. The letter O denotes the operating point, respectively. Such a characteristic can be easily obtained by applying the circuit shown in FIG. 4. Screened lamps 1 and 2 are connected by their anodes with control grids in parallel. Screen grids receive opposite voltage.

FIG. 5, an apparatus for obtaining balanced modulation is given on the above described linear principle.

The control grids of the pytelectrode lamps o and 4 (pentodes) are fed through a transformer 5 with a high frequency, and a modulating frequency is supplied to the terminals of the screen grids S in opposite phases, for example through a transformer 7 with a midpoint; From circuit 9 connected to the circuit in parallel with the connected anodes 10, the sum and difference side frequencies are removed.

In the case of pentodes, the modulating frequency can be supplied