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@vt.edu mailto:zleffke@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 _______________________________________________ Sent via AMSAT-BB@amsat.org <mailto:AMSAT-BB@amsat.org>. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via AMSAT-BB@amsat.org <mailto:AMSAT-BB@amsat.org>. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: http://www.amsat.org/mailman/listinfo/amsat-bb