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Radio input device with autotransformer connection

Lecture



Schematic diagrams.

Practically, three types of circuits with autotransformer coupling with antenna are used in the input devices of receivers: autotransformer circuit, dual autotransformer circuit, and circuit with series connection of inductance. In the first two schemes, the autotransformer connection of the antenna or feeder is made in the inductive, and in the third scheme - in the capacitive branch of the kennel. In all schemes, parallel circuits are used as a frequency-selection system.   Radio input device with autotransformer connection


a) In the autotransformer circuit, the necessary degree of communication with the antenna is carried out by choosing the transformation ratio   Radio input device with autotransformer connection

  Radio input device with autotransformer connection ,

  Radio input device with autotransformer connection .

  Radio input device with autotransformer connection

Figure 8.3.

The inclusion on the input side of the first cascade is complete, i.e. transformation ratio   Radio input device with autotransformer connection . In this case, the input active conductivity and the input capacitance of the first cascade of the receiver is fully connected to the circuit.

b) In the dual autotransformer circuit, the necessary degree of communication with the antenna is carried out, as in the previous case, by choosing the transformation ratio (inclusion)   Radio input device with autotransformer connection . In order to reduce the input active and capacitive conductances into the circuit, an incomplete connection of the input of the first cascade to the circuit is used, i.e.   Radio input device with autotransformer connection .

  Radio input device with autotransformer connection

Figure 8.4.

Incomplete connection of the circuit with the first stage can be implemented in the form of an autotransformer or transformer circuit or by communication through a capacitive divider. In an autotransformer or dual autotransformer circuit, the necessary transformation ratios are provided by tapping from a certain part of the turns of the inductance L of the circuit. With a known approximation, transformation ratios   Radio input device with autotransformer connection and   Radio input device with autotransformer connection can be determined from the ratios:

  Radio input device with autotransformer connection ;   Radio input device with autotransformer connection because   Radio input device with autotransformer connection .

The overall transformation ratio of the input device can be represented as:

  Radio input device with autotransformer connection ;

Where   Radio input device with autotransformer connection ,   Radio input device with autotransformer connection ,   Radio input device with autotransformer connection , - the number of turns in the inductor L or its parts   Radio input device with autotransformer connection and   Radio input device with autotransformer connection .

Selection of ratios   Radio input device with autotransformer connection and   Radio input device with autotransformer connection In the scheme, you can make the necessary degree of connection with the antenna, in particular, the chosen mode of matching or mismatch.

c) In a circuit with a series connection of inductance, double transformation is carried out in the capacitive branch of the circuit.

  Radio input device with autotransformer connection

Figure 8.5.

The circuit is used at frequencies above 200-300 MHz, when the loop inductor degenerates into one turn and the transformation in the inductive branch becomes practically difficult to implement.

The equivalent circuit of the input device with a series connection of inductance is as follows:

  Radio input device with autotransformer connection

Figure 8.6.

The diagram shows that the antenna is connected to a capacitor   Radio input device with autotransformer connection , and the input to the input of the first stage voltage is removed from the capacitor   Radio input device with autotransformer connection . Tank sizes   Radio input device with autotransformer connection and   Radio input device with autotransformer connection take into account the parasitic capacitance introduced respectively by the antenna and the input of the first stage. The capacitive branch of the circuit consists of series-connected containers   Radio input device with autotransformer connection and   Radio input device with autotransformer connection and parallel connected parasitic capacitance   Radio input device with autotransformer connection loop inductors, i.e. total contour capacity:

  Radio input device with autotransformer connection .

Transformation ratios, if we ignore the relatively small capacity   Radio input device with autotransformer connection , respectively, will be equal to:

  Radio input device with autotransformer connection ;

  Radio input device with autotransformer connection .

The overall transformation ratio in the input device, if the losses in the circuit itself are small, compared to the insertion, matters

  Radio input device with autotransformer connection .

It follows that the selection of the relationship   Radio input device with autotransformer connection and   Radio input device with autotransformer connection You can realize the necessary connection with the antenna, in particular, the selected mode of matching or mismatch.

Equivalent scheme.

From the above consideration it follows that all three autotransformer circuits are special cases of the dual autotransformer circuit. The common circuit for all these types of input devices is as follows:

  Radio input device with autotransformer connection

Figure 8.7.

In this diagram, the EMF source is presented in the form of a current generator.   Radio input device with autotransformer connection with internal resistance   Radio input device with autotransformer connection . Since the antenna is tuned,   Radio input device with autotransformer connection

The resulting capacitance of the circuit takes into account the capacitance of the circuit itself and the containers introduced from the first stage.

a) for autotransformer circuit

  Radio input device with autotransformer connection ;

b) for dual autotransformer circuit

  Radio input device with autotransformer connection ;

c) for a circuit with sequential inductance

  Radio input device with autotransformer connection .

The resulting capacitance of the circuit should be as small as possible. The inductance of the circuit is selected from the condition of providing resonance at a given frequency   Radio input device with autotransformer connection input device settings.

  Radio input device with autotransformer connection .

Load conductance is defined as

  Radio input device with autotransformer connection .

Input device parameters.

The input device parameters are determined by the formulas obtained for the generalized single-loop input device, taking into account the knowledge of the transformation ratios   Radio input device with autotransformer connection and   Radio input device with autotransformer connection .

Resonance gain

  Radio input device with autotransformer connection .

For tuned antenna   Radio input device with autotransformer connection - active conductivity of the antenna.

Then

  Radio input device with autotransformer connection .

Result Loop Loop

  Radio input device with autotransformer connection .

Where   Radio input device with autotransformer connection ;

  Radio input device with autotransformer connection ;

  Radio input device with autotransformer connection .

Trace the nature of the change   Radio input device with autotransformer connection on frequency   Radio input device with autotransformer connection . For this expression for   Radio input device with autotransformer connection we write in the following form:

  Radio input device with autotransformer connection .

In autotransformer circuits, the coefficients   Radio input device with autotransformer connection and   Radio input device with autotransformer connection practically independent of frequency. If we assume that within the subrange does not significantly change the quality factor   Radio input device with autotransformer connection and antenna impedance, i.e.

  Radio input device with autotransformer connection ,   Radio input device with autotransformer connection ,

then when rebuilding capacity   Radio input device with autotransformer connection grows with   Radio input device with autotransformer connection

  Radio input device with autotransformer connection

Figure 8.8.

Autotransformer circuits are simpler to manufacture and customize than transformer circuits. However, in these schemes it is difficult to implement small values ​​of transformation ratios (inclusions), especially when coordinated with feeders with low wave resistance. When the loop is rebuilt by the capacitor and the capacitance in the autotransformer circuit, only increasing character can be obtained   Radio input device with autotransformer connection from   Radio input device with autotransformer connection .


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Devices for the reception and processing of radio signals, Transmission, reception and processing of signals

Terms: Devices for the reception and processing of radio signals, Transmission, reception and processing of signals