Proposed in [1] the amplifier is a field effect transistor with Schottky barrier (MESFET) was tested for the reception of weak TV signals and has shown fantastic results. So, barely discernible image of the 9th channel Kamensk-Shakhtinsky repeater (100 km) when connecting this amplifier was restored almost to normal. For example, the two-stage amplifier transistors CT didn't give even close to this effect.

Antenna amplifier

Adapted for receiving TV diagram shown in Fig.1. The amplifier is resonant and tuned from 6 th to 12-th channels of the resistor R3. Coil LI is frameless and has 5 turns of wire sew 0,7 mandrel with a diameter of 7 mm. Allotment - 1 loop from below. I must say that the MESFET is very sensitive to static electricity, interference and network congestion at the entrance. Although the gate of the transistor and is connected to the case through the coil L1, the contact input X1 even a very small charge (from hairbrushes for example) causes its breakdown. Therefore, it is risky to connect a random antenna, especially with a split vibrator. The metal core of the power cable must be connected to the DC of the screen, and he, in turn, - with carrier mast. The power amp circuit Board shown in Fig.2.

The amplifier can be made broadband (Fig.3), enabling the input of a broadband transformer T1 with a conversion ratio of 1:9. T2 is intended to align the output resistance of the amplifier with the impedance of the cable, which increases the efficiency compared with the inclusion shown in Fig.1. The amplifier is not necessary to use powerful MESFET as in [1], instead of them nearly as good such as SP (AP). Transformer T1 is wound on the ring CHH 100 NN and contains 4 round three of PEV of 0.2. T2 - on the same core 4 of the coil in the two wires. In both schemes To - ferrite bead, dressed in the output flow to prevent self-excitation at microwave frequencies.

For the experiment can be replaced on a conventional MESFET low noise FRI KPA (with the appropriate correction R1 and R2). The difference is more than convincing.

Literature

1. S. Franklin (WВ5KGL), the Radio Amateur. - 1992. - N3. - P. 46 - 47.

Author: A. Ryzhkin; Publication: www.cxem.net

Add comment

Menu

Service manuals

Copyright © 2018 Electrical circuits.