On 9/6/2007 9:33 PM, Robin van Spaandonk wrote: > In reply to Harry Veeder's message of Sat, 09 Jun 2007 22:07:05 -0500: > Hi, > [snip] >> Many years ago, before ipods and mp3 players, I had a sony walkman with a >> radio turner. >> I found that if a pocket calculator were switched on and placed on top of >> the walkman I could >> move the tuner's dial to particular frequency and hear a faint >> "thump.......thump.......thump..." >> sort of like a heartbeat. Different calculators generated a similar pattern >> of sounds. >> >> What was going on? > [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"? Harry
