1n4001 are not suitable) and a 10n capacitor. This signal is turned into a DC level by the use of a low voltage drop diode (a germanium type would be ideal, silicon types e.g. Each op amp also acts as a low pass filter, attenuating frequencies higher than 72kHz, which helps us a lot.Īfter this we’re at point 2 in the schematic and we have a big 60kHz signal. The gain of each op amp is set to -214 (the – indicates that there will be a phase shift, we don’t care about phase so that’s ok). After a DC blocking capacitor there are two identical stages of op amp amplification. The JFET’s gain is set to 10 by the 1k and 100R resistors. This has an extremely high input impedance, which is exactly what we want. The first stage of amplification is a JFET (2N3819). This signal is obviously tiny though, so we amplify it. We can’t really change L, it’s set by the ferrite rod antenna (code LB12N from Maplin) Once you have found a C value to set f as 60kHz (I found C to be around 840pF), they will resonate and you’ll be receiving any 60kHz signal in the air. As far as receiving the signal is concerned, the ferrite antenna and two shunt (parallel) capacitors adjust the frequency that they resonate at, according to this equation: A 7809 9v voltage regulator brings this down to 9v for our needs, there’s no need for a heatsink on the regulator if it’s the 1A type. Firstly the power for the receiver comes from the PSU/decoder, and can be around 13-20V. The circuit should be fairly self explanatory. You could use it as a simple receiver for other frequencies by just taking the signal at point 4 and adjusting the Inductor (antenna) and shunt capacitor to match the frequency you wish to receive. This schematic is essentially a sensitive 60kHz receiver and ASK demodulator. Shown on the left ( click it to enlarge) is the circuit diagram for the receiver part of the clock – click it to make it readable or download it.
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