Hello
I have just designed and built the following simple AM superhet receiver.
and
It is just to receive the station on AM 1026KHz. The Mixer is a switching mixer and literally just switches the signal on/off at 216KHz using a 7555 timer and CMOS 4066 analog switches which are switched via buffer/inverter as required.
I am aiming to select the first IF on 810KHz, however my IF filter (a tuned common emitter stage) is obviously nowhere near selective enough. The receiver works but virtually certainly just detects the original station frequency of 1026KHz.
I hear there are specific steep-sided bandpass filters for 455KHz but am having difficulty sourcing these. –Would be very grateful if any reader knew of a source.
Also, since I will need to raise my mixer switching frequency to 571KHz, I wondered if readers may know if the CMOS 4066 analog switch’s that I’m using will switch at this rate? -the datasheet does not define this. –and whether a different switch would be more appropriate. Also, the “Practical Oscillator Circuits” book says that the 7555 is recommended “up to 500KHz and perhaps more” and wondered if anyone has ideas for a higher frequency square-wave oscillator (50% cycle)? –preferably one that has a slightly variable frequency so that I can ‘tune’ it to hit on the centre frequency of the IF filter.
I have just designed and built the following simple AM superhet receiver.
and
It is just to receive the station on AM 1026KHz. The Mixer is a switching mixer and literally just switches the signal on/off at 216KHz using a 7555 timer and CMOS 4066 analog switches which are switched via buffer/inverter as required.
I am aiming to select the first IF on 810KHz, however my IF filter (a tuned common emitter stage) is obviously nowhere near selective enough. The receiver works but virtually certainly just detects the original station frequency of 1026KHz.
I hear there are specific steep-sided bandpass filters for 455KHz but am having difficulty sourcing these. –Would be very grateful if any reader knew of a source.
Also, since I will need to raise my mixer switching frequency to 571KHz, I wondered if readers may know if the CMOS 4066 analog switch’s that I’m using will switch at this rate? -the datasheet does not define this. –and whether a different switch would be more appropriate. Also, the “Practical Oscillator Circuits” book says that the 7555 is recommended “up to 500KHz and perhaps more” and wondered if anyone has ideas for a higher frequency square-wave oscillator (50% cycle)? –preferably one that has a slightly variable frequency so that I can ‘tune’ it to hit on the centre frequency of the IF filter.
