Research website of Vyacheslav Gorchilin
All articles/Electronic circuits
Generator to long lines in several modes
This generator can work with different loads and modes: from small pigtail length of 20 cm in long line mode to the inductor in the resonance mode of the first or of the second kind (RVR). In some cases, the generator operates with the NMR conductor, behaves in the most non-classical way and affects nearby equipment. It is another variant of the circuitry of the generators of a single transistorworks in a wide range of supply voltages (5..70), contains a minimum number of parts and is suitable for a wide range of research tasks.
The General oscillator circuit shown in figure (1a). The transistor VT1 is included in the circuit of high frequency "according to the scheme with a common base", which is grounded through a capacitor C1. The chain of resistors R1-R2 gives her a positive offset and a positive feedback arises due to the capacitance C3 connected between the collector and emitter of the transistor and the inductor L2. The capacitor C2 smoothes out any ripple from the generator and closes the feedback circuit of the power that is supplied to the connectors XS1-XS2.
Fig.1. Options include generator, a — coil inductance b — long line c — with external control.
As we can see on the schematic there is no capacitor connected in parallel to L1 and forming a classical oscillating circuit. You will be surprised, but if such a capacity to connect, then the effect will turn out completely the opposite: instead of reducing the frequency generator will switch to other mode, and will dramatically increase the frequency of the output pulses. In addition, the absence of such a capacitor allows to fully reveal the wave properties of a coil or a long line (L1 in diagram).
As a L1, you can connect two inductors.
1. Long line. It could just be a pigtail length of 20 cm and more. Interestingly, in the case of twenty centimeters of length of the conductor, the oscilloscope can display frequency on L1 is of the order of 5-20 MHz, although a quarter of a wavelength at this frequency, comprising from 4 to 15 meters. Moreover, even under small power (3-4 watts) the lower the circuit output L1 can severely burn the skin when touched. The latter effect applies to the next view loads.
2. Inductance coil. Here fit all types of wound coils. Especially well shown flat Tesla coil [1]. For all types of inductively very desirable high quality factor. For example, if the circuit L1 to set the resistance even a small amount (5-15 Ohms), the generation may not start.
Modes of operation of the generator
1. The burst pulse. Although the circuitry of the generator has no low-frequency chains, under certain conditions it can give packets of pulses, and frequency of bundles can be quite a low frequency down to audio frequency. In this case, the frequency of fill packs will be conventional for the selected inductance. This mode can be obtained with low values of the supply voltage of 3-4 V, either when the inductance L1 is larger than the inductance L2. This mode differs above the lowest consumption.
2. Sinusoidal oscillations. Not the main mode of operation. Is a transition between the first and subsequent third mode while gradually increasing the voltage.
3. The RVR mode. Primary and stable mode of operation. While in L1 it is possible to observe the unipolar emission of relatively large amplitude. It can be achieved by increasing the power supply, tuning resistor R1 and a parallel connection L1 small capacity, for example, 1 nF.
4. Mode NMR. It can also be achieved by adjusting resistor R1 and a parallel connection L1 capacitance on the order of 1-10 nF. Different from the previous unstable amplitude emission, the frequency of which does not depend on the inductance L1. The regime has a huge impact on the surrounding radio equipment: it can begin its rebooting or off, and in the speakers there is a strong hum. In addition, if the power source of the digital generator, the readings of consumption can be greatly reduced or even be zero.
In the second and third mode in a relatively short length of the load wire L1 (Fig. 2b) obviously, there are additional modulation fluctuations in the range of extremely high frequency (EHF). They are based on the combined effect of the crystal of the transistor and the long line L1.
External control
The generator may very well be controlled by an external device. For this displacement it is necessary to apply output from this device (Fig. 1c). If this device will also be the alternator, the output (L1 scheme) you can get a quality modulated oscillations.
Mode of generation is very important to choose the transistor VT1. Very well suited high-voltage fast switching npn transistors, such as 2SC2625. They provide high efficiency of the entire generator and if the power of order 1W can be put on a radiator. With less efficiency work popular transistors 2SC5200.
Special attention should be paid to the capacitor C3. He must be high, otherwise it can bask and it greatly reduce the efficiency of the entire installation. Here is good tube condenser for radio transmitters. The other capacitors can be ceramic or film.
Inductor L2 is possible to apply the standard, for example like this. It is advisable to choose one that has a lower resistance, so less loss.
Installation and setup
Installation must be performed according to the same rules as for microwave devices: minimum length when coupling between the circuit elements and the lack of protruding ends and hangnails. The adjustment of the generator is reduced to establish the voltage at which is achieved the desired mode of operation. Also, it is possible to adjust resistor R1.
The materials used
  1. Coil for electro-magnets. US512340, 1894.