[amsat-bb] FM signal on FO-29?

[Zach Leffke]

Good point Bob.  I haven't fully worked through the problem yet, but 
thats pretty much right in line with what I'm thinking.  Thats what I 
meant by saying watching the 'rate of change of doppler.'  When the 
slope of the doppler s-curve is at a maximum, that should be the point 
of closest approach.

Actually, that brings up a question.  Do you know what type of equation 
would fit the doppler S-Curve profile?  something that could be used to 
generate a regression equation from a few doppler observations?

-Zach, KJ4QLP


On 11/08/2015 06:12 PM, Robert Bruninga wrote:
> Zach
> You dont need to know the senders exact freq, just a plot of his freq 
> during the pass will form an "S" curve and once you have enough of the 
> "S", you can know his center freq, and hence his closest point of 
> approach.  That gives a line of bearing.  Anothe pass gives another 
> one, and so on...
>
> bob
>
> On Sun, Nov 8, 2015 at 5:54 PM, Zach Leffke <zleffke at vt.edu 
> <mailto:zleffke at vt.edu>> wrote:
>
>     well.. when I say students, I meant graduate students at VT that
>     happened to be in the lab when I was doing the experiment.  They
>     work with me and Bob, so a few crude words here and there aren't
>     uncommon to them.
>
>     But good point, probably not the best thing for a public demo if
>     your audience is a bit younger.
>
>     Actually, I've seen so much FM activity (basically every time I've
>     monitored FO-29 since we first came online in late september) that
>     I've been toying with the idea of trying to locate where the
>     source emitters actually are located based on doppler shift data. 
>     We know the doppler between the receiving ground station and
>     FO-29, so we can back that out.  We know the transponder mapping,
>     so we can work through that to determine what the center frequency
>     is as the signal enters the transponder uplink receiver.  What we
>     don't know is the uplink doppler, because we don't know where the
>     emitter is and we don't know what exact center frequency they are
>     on (but I bet you its in 5kHz steps, maybe 2.5kHz).  So we have
>     two unknowns. I'm betting there's a way to work through it though,
>     and with enough observations and by watching the rate of change of
>     the doppler, I bet there's a way to make an educated guess on what
>     their center freq and location are.
>
>     Or if someone listening knows Spanish and/or Portugese, maybe we
>     could get lucky and hear what cross streets the taxi is going to
>     (if it is in fact a taxi).
>
>     -Zach, KJ4QLP
>
>     On 11/08/2015 05:30 PM, Clayton W5PFG wrote:
>
>         I wouldn't recommend playing the FM audio heard via FO-29 to a
>         group of children. Normally it's not English.  It's most
>         likely NOT a religious broadcast based on their choice of
>         crude words.
>
>         73
>         Clayton
>         W5PFG
>
>         On 11/8/2015 16:13, Zach Leffke wrote:
>
>             So yes, in the last couple weeks I've seen a LOT of FM
>             activity on
>             FO-29.  And based on my experience with Friday's pass,
>             which was
>             ascending, I'm leading towards the Central/South America
>             QRM theory.
>             Lots of strong FM activity as the pass started and the
>             satellite was
>             over the lower latitudes, but as FO-29 ascended over
>             higher latitudes
>             towards the north pole, the FM activity died down.
>
>             -Zach, KJ4QLP
>
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