So far this is exactly like an AM crystal radio. One end of the parallel configuration of L and C connects to an antenna (surprisingly long!) and the other end connects to a ground wire which is tied to the AC outlet ground (old books tell you to ground it to a water pipe). Here’s how the circuit works: The AM radio signal is tuned by inductor L, which is 300 turns of wire on a 1/2 inch diameter cardboard tube made out of a paper roll, along with the 100pF variable capacitor.
You may be wondering how all this is accomplished with a 555. The tuning is accomplished with an inductor and a capacitor, and the LM555 acts as an AM demodulator and class-D power amplifier to drive the speaker. The only active device (silicon, germanium, or otherwise) is the LM555. 9V battery fits neatly inside a 30mm x 130mm long PVC tube.ĪM radio built around 555 timer chip. Insertion of earphones plug completes supply circuit and acts as an on/off switch. LM358 dual op-amp draws less than 1 ma so the battery drain is minimal. The two 10M resistors bias the detector diode and the op-amp input near mid-rail for better detector efficiency. Detector uses a biased 1N5711 (or similar) schottky diode with lowest forward-biassed voltage drop.
Capacitance runs from 28 to 7pF which by formula gives a frequency range of 77 - 155MHz. Tuning capacitor is a 30pF Philips Beehive trimmer, with a short length of plastic tube glued - as a tuning shaft. The input tuned cct 'L' is a 2 turn loop, with 30mm diameter measured at 0.15uH on my LC Meter which intercepts RF directly as opposed to an LC cct fed with external aerial. Useful for listening to the pilot transmissions. For many readers, AM broadcast is becoming a thing of the past, so we’re not sure we’ll see this very often.This passive airband receiver is basically an amplified "crystal radio" designed to receive nearby aircraft transmissions on 121 - 133 MHz frequency. The video may be long, but it’s worth a look for the vintage parts if not for the quality of radio stations on the air today in California. Along the way, he damages one of the IF transformers and has to replace it with a modern equivalent, which we would have concealed under the can from the original.
TRANSISTOR FM RADIO RECEIVER CIRCUIT FULL
We’re treated to the full process of aligning a superhet receiver through the relatively forgiving low-frequency medium of a medium-wave radio. First up are a set of very tired electrolytic capacitors whose replacement restores the volume, and then it’s clear from the lack of stations that the set has a problem at the RF end. The video below the break is a long one that you might wish to watch at double speed, but it takes us through the now-rare skill of fault-finding and aligning an AM radio receiver. brings us a transistor radio from that era, a Jewel TR1 from about 1958, that despite its four-transistor simplicity to our eyes would have been a rare and expensive device when new.Īs you’d expect, a transistor radio heading toward its 70th birthday requires a little care to return to its former glory, and while this one is very quiet it does at least work after a fashion. Back in the 1950s the semiconductor industry was in relative infancy, and at the consumer end electronics were largely synonymous with radio. Here in 2023 the field of electronics covers a breathtaking variety of devices and applications, but if we were to go back in time far enough we’d enter an age in which computers were few and far between, and any automated control systems would have been electromechanical at best.
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