Really interesting analysis, James. I'll need to do some checking to determine my distance from W1AW, and where that puts me in the skip zone.
John ---- James Maynard said the following on 11/19/2006 02:08 PM: > John Ackermann N8UR wrote: >> Without giving away any actual numbers, did anyone else notice either a >> fuzzy signal, or some interference within about 1 Hz of W1AW on 40M? >> >> I recorded the entire test run and have been unable to prove to myself >> exactly where W1AW is; almost any sample of data I select shows two >> signals within about 1 Hz -- depending on just what segment of the data >> I analyze, I can sometimes get one peak that is sharper and another that >> is smeared out over about 0.5Hz, but I'm not confident about which one >> is the real thing. An FFT with enough bins to separate the two signals >> loses the CW keying, so I can't use that to see which one is real. >> >> Again, nobody post actual frequencies, but if you've looked at the 40M >> signal very closely, I'd appreciate finding out whether this is local to >> me, or something others saw. >> >> Thanks, >> >> John >> >> _______________________________________________ >> time-nuts mailing list >> [email protected] >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >> >> >> . >> > For me, the W1AW signal was quite faint. It was visible on Specturm > Lab's waterfall display as a rather broad, fuzzy trace, but I could not > copy it by ear. (I did, once, hear the call sign, W1AW.) So my > measurement of its frequency was by averaging the Sprectrum Lab text > output (File | Text file export... | Export of calculated data) after I > had imported into a Microsoft Excel file. I computed a mean of the data > in one of the spreadsheet columns to get the frequency that I used in my > FMT submission. I also computed the standard deviation of that column, > and saw that it was spread over several hertz. > > You were closer to W1AW, and had a stronger signal to work with than I. > But I surmise that were seeing the same phenonemon: ionospheric doppler > -- and especially the effect of multipath on the doppler-shifted signal. > > Suppose that, at the time of the FMT, the ionosphere was rising. (It > usually does at and after sunset.) I assume that you were beyond the > ground-wave coverage zone of W1AW, but were getting it on sky-wave. > Let's denote the frequencies of the W1AW signal as transmitted (or > received on ground wave), and after one-hop, two-hop, etc. skywave > reflections as follows: > > f0 = transmitted frequency = frequency as received on groundwave > f1 = frequency as received after one reflection from the ionoshphere > f2 = frequency after two reflections > f3 = frequency after three reflections > etc, > > If the ionosphere is moving, f1 will differ from f0 by some amount that > depends at the rate at which the ionosphere is moving. For two-hop > reception, f2 will differ from f1 by a similar amount -- but not exactly > the same, because of differences in the angles of incidence to the > reflecting surface. > > I surmise that the strongest signal you received was proably W1AW as > received at frequency f1 (after one hop) and the second, fainter trace > was W1AW as received at frequency f2 (after two hops). You are probably > beyond the zone of ground-wave reception, so you did not receive W1AW at > its actual transmitted frequency, f0. > > Which leads to an interesting possibility. If you assume that the > difference, f1-f0, is almost the same as the difference, f2-f1, you may > be able to use this information to infer the true transmitted frequency, f0. > > I, on the other hand, had such faint and blurred reception that I was > unable to discrimate between f1, f2, f3, etc., and so could not try to > compute f0. > _______________________________________________ time-nuts mailing list [email protected] https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
