On Sat, 08 Aug 2009 22:35:42 -0700, Brett Howard wrote: >I liked Joe's comment about it being spaced over more bandwidth. Thats >an interesting thought but based on the whole logarithmic scaling stuff >it does make sense.
While Joe is rarely wrong, he is wrong about this, and Lyle is right. In nature (that is, at the input of your K3) the noise voltage is spread out over frequency. When you narrow down the IF, you receive less of that noise. As you widen the filter, the noise rises in direct proportion to the bandwidth. So when you narrow the filters, you are improving the signal to noise ratio. The fundamental problem of narrowing the filter is a psychoacoustic one -- that is, the ability of the human ear/brain being able to separate signal from noise. When you narrow the filters, the only noise you hear has the same frequency components as the signal, so the brain is trying to separate signal and noise that are very close to the same pitch. BUT -- human hearing is logarithmic, both in pitch and amplitude. Our ability to separate frequencies is based on proportional differences in frequency, so setting the CW pitch to a lower frequency gives the ear greater ability to separate signals (or signal and noise) that are close together in frequency. That is, if the pitch is set to 500 Hz, 100 Hz bandwidth is 20% of the signal frequency, whereas at a pitch of 1 kHz, 100 Hz bandwidth is only 10%. I know some really good CW operators (N6RO is one) who regularly work at pitches below 500 Hz for this reason. BTW -- I know exactly what the original poster of this thread is talking about -- I really suffered from it when I lived in Chicago. 73, Jim Brown K9YC ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
