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

Mon Nov 9 14:54:47 UTC 2015

No, I’m all talk and no do… compared to whiz kids and Matlab…  Im old
fashioned enough to just plot it on graph paper and LOOK for the middle hi
hi…

*From:* Zach Leffke [mailto:zleffke at vt.edu]
*Sent:* Sunday, November 08, 2015 6:55 PM
*To:* Robert Bruninga
*Cc:* amsat bb
*Subject:* Re: [amsat-bb] FM signal on FO-29?

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> 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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