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Amplitenna (TEL064E)

   Although the analogue TV stations in the VHF range tend to disappear, in the interior, we still have a predominance of the devices of this type and with them the reception problems. We also have the problem of reception with FM stations that occur in regions of weak signals. The circuit we propose is an amplified antenna for FM and VHF.

   Weak signals in the VHF range cause problems with images with drizzle and other problems in analog TV.

   In the FM band we have problems of distortions and even signs that oscillate, disappearing at certain moments.

   If you have these problems, we describe a small amplifier that you interlace between the antenna and the receiver and that can help a lot.

   Of course the circuit will work in cases where the signal reaches an antenna, not solving the problem if we have no signal to amplify.

   Ideally, the circuit should be positioned next to the antenna, with the long power lead going to where the source is.

   The circuit has a good gain in the frequency range of 50 to 150 MHz.

 

   Assembly

   In figure 1 we have the complete diagram of the antenna amplifier.

 

   Figure 1 - Full diagram of the amplifier
   Figure 1 - Full diagram of the amplifier

 

   In figure 2 we have a suggestion of printed circuit board for its assembly.

 

Figure 2 - Printed circuit board for mounting
Figure 2 - Printed circuit board for mounting

 

   On assembly, observe the position of the transistors and the polarity of the diodes.

   The Capacitors should all be ceramic and the resistors 1/8 W with any tolerance.

   The coil L2 consists of 3 turns of rigid telephone wire with a 1 cm diameter without a core.

   L1 consists of two turns of the same wire connected in L2 as shown in the figure in which we have the printed circuit board.

   XRF1 is a shock of 1 uH or can be "fabricated" by winding about 5 turns of wire 32 or close on a toothpick.

   The trimmers can be of more modern types from 2-20 to 4-40 pF round plastic, and modifications of the design of the board to accept this type of component should be made if used.

   In Figure 3 we have a power supply for the circuit, although it can also be powered by a small 9 V battery.

 

   Figure 3 - Power supply for the circuit
   Figure 3 - Power supply for the circuit

 

   The consumption is very low, and any transformer with secondary can be used from 50 mA.

   The LED indicator that the power is on is optional.

   In figure 4 we have the way of connecting the circuit between the antenna and the receiver.

 

   Figure 4 - Connecting the circuit to the receiver and antenna
   Figure 4 - Connecting the circuit to the receiver and antenna

 

   To use, simply tune to the desired station and adjust trimmers and trimpot for better reception.

   

 

Q1 - BF198 or equivalent - RF NPN transistor

Q2 - BFY90 - RF NPN Transistor

D1, D2 - 1N4148 - silicon diodes of general use

R1, R2, R3 - 10 k ohm - resistors - brown, black, orange

R4 - 220 ohm - resistor - red, red, brown

P1 - 4k7 ohm - trimpot

C1, C6-10 nF - ceramic Capacitors

C1, C3, C4, C5-1 nF - ceramic Capacitors

C7 - 100 nF - ceramic capacitor

CV - trimmers - see text

XRF - 1 uH - shock - see text

L1, L2 - Coils - see text

Other Materials:

Printed circuit board, mounting box, power supply or battery, wires, solder, etc.