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

[Robert Bruninga]

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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