In reply to Harry Veeder's message of Sun, 10 Jun 2007 12:16:47 -0500: Hi, [snip] >> Calculators have their own inbuilt "clock" which is a quartz oscillator, and >> also divider circuits, so they produce a number of radio frequencies. If the >> Walkman is tuned to a frequency close to one of those generated by the >> calculator, then a slow difference frequency will be generated which could be >> the thump-thump sound. >> >> Regards, >> >> Robin van Spaandonk >> >> The shrub is a plant. >> > >ok, thanks for that explanation, but can you say bit more about "difference >frequency"?
When two frequencies affect one another, then modulation occurs, and as a consequence both sum and difference frequencies arise. If the two frequencies happen to be very close together, then the difference can be quite low and easily audible. You can hear this when slowly tuning an AM radio in to a weak station. There is a whistling sound, which drops in pitch as you get closer to the station, well at least there used to be on old radios. In modern radios, I think they build in suppression circuits which prevent any sound coming from the speakers until you are actually directly on the station. Regards, Robin van Spaandonk The shrub is a plant.
