[time-nuts] FMT -- 40M strangeness?

James Maynard james.h.maynard at usa.net
Sun Nov 19 19:34:39 UTC 2006


You might also look over your data, and, if you captured a screen image, 
that image.  I assume that the ionoshpere was rising at the time of the 
FMT.  If that is the case, then f1 should be lower in frequency than f0, 
and f2 lower in frequency than f1.

If, however, the fainter trace is *higher* in frequency than the 
stronger trace, and especially if the fainter trace is *narrower* than 
the stronger trace, then the fainter trace may be groundwave reception 
at the transmitted frequency, f0.

-- 
James Maynard, K7KK
Salem, Oregon, USA


John Ackermann N8UR wrote:
> 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
>>>time-nuts at febo.com
>>>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.
>>
> 
> 
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