Pristavka-ostsilograf to the TV.

The Ostsillografichesky addon does not demand intervention in the TV circuit (it is connected to an antenna nest of the TV). Together with the generator of shaking frequency it can be used for adjustment of PCh amplifiers of radio receivers.

The addon can be considered (fig. 1 and 2) as the tiny television transmitter. Despite relative simplicity of the circuit in this transmitter the full television signal which differs from a standard signal only lack of equalizing impulses is formed.

Puc.1 - the Block diagram of an ostsillografichesky addon

Personnel clock pulses are formed of alternating sinusoidal voltage by the amplifier limiter (Т1), a differentiating chain of R8C4 and the threshold amplifier (T1). Their duration about 1,9 мсек.

Puc.2 - the Schematic diagram of an ostsillografichesky addon.

The blocking oscillator on the transistor of Gz generates lower case clock pulses. It not the main impulses of the blocking oscillator, and the emissions of collector tension arising right after main. Between collectors of transistors T4 and T5 the dividing D3 diode is switched on. At the moment of generation of the main impulse the collector of the T4 transistor becomes isolated on the chassis via the open T5 transistor and the D3 diode.

Thereof in personnel clock pulses there are inserts which, as well as it is required, precede lower case clock pulses. Windings of the Tr1 transformer of the blocking oscillator are reeled up on the toroidal core from an oksifer (H=1000). External diameter of the core of 10 mm, and. thickness of 2 mm. Windings of I and III contain on 100 rounds, ll - 30 rounds of wire ПЭЛШО 0,1.

At the beginning of the period of lower case development the impulse of tension of the blocking oscillator quickly charges the C5 condenser via the D2 diode. During other part of the period it is slowly discharged via the R6 resistor. Sawtooth tension arising thus arrives on base of the T2 transistor. Here it develops with ostsillografiruyemy tension.

The three-cascade amplifier (Т2, T3, T6) because of big factor of strengthening (50000-100000) works practically in the relay mode, being characterized with a certain threshold of operation. As on entrance sawtooth tension of the amplifier ostsillografiruyemy tension is imposed, switching of target tension coincides on time with the moment when total tension passes through a threshold of operation of the amplifier.

Time of increase of the front of impulses of tension on an exit of the amplifier is not enough besides because of high factor of strengthening. The moment of emergence of these impulses during the period of lower case development is defined by instant value of ostsillografiruyemy tension. Parameters of an addon are chosen such that in the absence of studied tension the axial line is in the screen center. If necessary the image on the screen can be shifted in this or that party change of resistance of the R3 resistor.

For increase of image sharpness of the line on the TV screen the amplifier (T2, T3, T6) is captured by positive feedback from the T3 transistor collector on base of the T2 transistor via the C6 condenser. It considerably increases strengthening in the field of high frequencies and, therefore, increases a steepness of the front of target impulses. Visually it is shown in the increased sharpness of transition from white to the black.

Personnel, lower case and videopulses develop on an entrance of the emitterny repeater (Т7) which is the VHF modulyatsionny amplifier of the generator (Т8). The last is accurate according to the circuit of a capacitor three-point. Frequency of generation should be chosen to equal bearing frequency of the image of a free television channel. Otherwise the addon can create hindrances to operation of the next TVs. Demanded frequencies of generation can achieve, selecting number of rounds of the L1 coil. At control for the second television channel (59,25 MHz) the L1 coil contains 5 rounds of a wire of PEV 0,6, diameter of the coil of 9 mm.

Modulated VCh tension arrives on an addon exit through a divider of R18-R19 which lowers tension to 3 мв in order to avoid VCh overload - a TV path.

Addon exit a coaxial cable or the braided double wire connect to an antenna entrance of the TV.

Design and adjustment. All details of an addon, except for generator VHF, it is possible to arrange on an assembly payment in any order. The details relating to VHF to the generator (C11-C15, L1, T8) should have short conclusions incorporate among themselves short conductors, and besides, it is necessary to group them in one place.

Any ekranirovka of an addon it is not required. After its inclusion it is necessary to adjust as usual the TV by means of adjusting handles (frequency of shots, frequency of lines, contrast). If frequency of impulses, the blocking oscillator of an addon does not lie in a range of adjustment of frequency of lines of the TV, it is necessary to enter it into this range, changing in small limits resistance of the R14 resistor.

It should be noted that synchronization of development of the TV from an addon usually turns out very steady therefore bad synchronization at adjustment of an addon indicates any mistake in installation. To achieve exact setup U K B of the generator of an addon for the chosen television channel, it is necessary to stretch or compress rounds of a winding of the L1 coil (that is to change a winding step). At the correct control the line on the screen is sharply outlined.

Parameters of an addon are picked up so that the greatest scope of the image on the screen of the TV corresponds to entrance tension about 0,3 century. Sensitivity of an addon can be regulated, changing resistance of the R2 resistor.

For check of sensitivity of an addon on its entrance submit an alternating voltage of known size or from the power supply tension of 6 B, frequency of 50 Hz through a divider, or from the sound generator.

Entrance resistance and sensitivity of an addon at desire can be raised considerably, having connected to it the LF usual amplifier with the emitterny repeater on an entrance.

Source: Radio 4-68
Author: Инж. Century. Wrens