[amsat-bb] FM signal on FO-29?
zleffke at vt.edu
Sun Nov 8 23:55:00 UTC 2015
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?
On 11/08/2015 06:12 PM, Robert Bruninga wrote:
> 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...
> 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.
> 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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