Hi Bob, >As long as we are discussing hearing cw I'd like to ask a question that has >been bothering me for many years. I am very sensitive to chirp, and that is >not what I am referring to. When I listen to a good cw signal in the range >of about 20-35 wpm I heard the dots and dashes as at slightly different >frequencies. This may simply be some sort of psychological quirk unique to >me. I am not even sure "slightly different frequencies" or tones is correct >way to describe it. Realizing that I am not listening to a sinusoidal tone >but sequences of short and long symbols and that long strings of dots will >have wider sidebands than long strings of dashes, I wonder if this is >relevant in any way. Most likely it is some sort of personal quirk. But I >wonder if anyone on this reflector by any chance notices anything similar or >has an explanation?
Let's say the dots are 40 msec long - that's 12.5 dots per second. The fundamental frequency is 12.5 Hz of course, with all the odd harmonics (37.5, 62.5 ...) So if you tune to hear this as 600 Hz, your actually hearing 600Hz+12.5Hz, 600Hz-12.5Hz, and 600Hz+37.5Hz, 600Hz-37.5Hz and so on depending on keying waveshape and receiver filter setting. So, dashes must then be 120 msec long, but with only 40 msec space between. That comes out to 6.25Hz. So what you hear is 600Hz+6.25Hz, 600Hz-6.25Hz, and the odd harmonics 600Hz+18.75, 600Hz-18.75, and so on, and certain even harmonics, since this isn't really a square wave. How much power is in each harmonic depends on the waveshape.... But - let's say your hearing or filter settings don't have a perfect flat response around 600 Hz. To exagerate, lets just cut off everything below 600 Hz. You might then hear dashes as 606.25 Hz, and dots as 612.5 Hz. That's a difference of 1% or so, and about 17 percent of the difference between two notes on a piano. The effect would get bigger as you move the center frequency down. You would be able to hear the change. 73, Michael, AB9GV _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com
