Conrad Course material 10090 14 years and over 10090 Manual De Usuario
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10090
Higher Amplification
Install the 220 μH coil again to receive the entire medium wave area.
In particular in the evening, you may receive many European stations. Radio sensitivity greatly
depends on the size of the aerial loop.
Another important factor is dampening of the oscillating circuit by unavoidable loss in the wire
resistance and the ferrite core. The more HF energy is lost, the lower the volume and the lower
selectivity will be. The receiver-IC TA7642, however, provides active de-attenuation, i.e. part of the
amplified HF signal is returned to the oscillating circuit to balance out this loss.
The amplification of the TA7642 and therefore also de-attenuation, may be adjusted via the operating
current within a certain range. The receiver output therefore drops a little as the battery weakens.
Vice versa, amplification can be increased by using a smaller initial resistor. Replace the 1-k
Ω resistor
by a 820
Ω resistor (grey, red, brown). Even higher amplification can be achieved with the 620 Ω
resistor (blue, red, brown). Caution: If the amplification is too high, the circuit will start natural
oscillation. You will then hear a loud interference whistle. In this case, increase the resistor again.
oscillation. You will then hear a loud interference whistle. In this case, increase the resistor again.