I wrote: >> Narrow-band filters seldom sharpen wide band material, like ticks. to which Walter Nissen replied >I am operating outside of my range of experience, but the "Time and >Frequency User's Manual" seems pretty clear on this matter. "Tick" is >apparently a euphemism, or approximation to the impression of the >received sound. In fact, the manual actually uses the word tick with >double quotes around it, "tick". Each WWV tick consists of 5 ms of >1000 Hz (WWVH 1200 Hz, CHU 300 ms 1000 Hz). So, even if there is some >spread, the received audio frequency of the signal should be highly >concentrated in the region of 1000 Hz. It would indeed, and a 1 kHz wide notch filter would transmit only the envelope. I was a ham operator for about fifteen years*. The narrower the filter band the more an AM voice signal sounds like it is coming from someone down a well. Narrow band filters are very useful for CW (code) reception where the relevant signal has much lower frequency components. It still sounds like it's coming out of a well, but that's the narrowing of the bandwidth of the background noise. Leigh *ages 15-30.