I measured the 2nd and 3rd harmonic of WWV's 600 Hz tone this morning using an HP 8568B spectrum analyzer set at 15 MHz, 30 Hz resolution, connected to an antenna. This avoids the harmonic generation that might be found in a receiver's audio stages, for example, such as when measuring tone levels with a computer sound card connected to a receiver's line out or headphone jack.
The 2nd harmonic at 1200 Hz is approximately 18 dB down from the 600 Hz sideband. The 3rd harmonic at 1800 Hz is about 30 dB down from the 600 Hz sideband. It's difficult to be precise in these measurements because all the modulation sideband fade independently to some degree and because the 1800 Hz harmonic is not too much above the noise floor at the moment. Averaging is difficult because the modulation changes frequency according to the schedule, 500 Hz, 440 Hz, 600 Hz, etc. So, yes, WWV has some distortion products. Jack K8ZOA On 11/8/2011 10:29 AM, Bob Cunnings wrote: >> Those tones are not sine waves. > I wasn't so sure about this. Over the years I've never heard this > mentioned, and technical references like NIST 25-67 and 668 describe > the audio tones as being derived from the cesium standards, with no > mention of harmonic content. So I sent an email to WWV asking if the > audio tones were generated as pure sine waves or had harmonic content > added intentionally. I quickly received this response: > ------------------------------------------------------ > Thanks for your email. > > The audio tones on the WWV broadcast are derived from the station > frequency standard, and are pure sine waves. > > Detailed information on the WWV broadcast can be found in NIST > publication SP432, available for download on the webpage: > http://tf.nist.gov/general/pdf/1383.pdf > > Sincerely, > Glenn Nelson > National Institute of Standards and Technology > Radio Stations WWV/WWVB > ----------------------------------------------------- > > I also see the harmonics on the P3. Unless Mr. Nelson is misinformed, > I suspect that it may be the "harmonics" are distortion products, > either transmitter IMD or artifacts of the receiver (P3 in this case). > BTW the publication he mentions is a very good read for WWV listeners. > > Bob NW8L > >> Those tones are not sine waves. They have distinct harmonic content >> that makes them a little "sharp" sounding, rather than the soft sound >> of a pure sine wave. What you're looking at is the components that >> make it sound that way. > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:Elecraft@mailman.qth.net > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
