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

Zach Leffke zleffke at vt.edu
Mon Nov 9 21:20:01 UTC 2015

```Hi Daniel,
Thanks for the info.  I'll look into it more when I get a free
moment.  And for the cubic thing, I just meant that it appears that the
doppler S-curve looks like a third order polynomial over the course of a
full pass.  After a quick google search, the first image at this link is
what I mean (in this case envision time along the y axis and doppler
offset along the x axis).

http://www.biology.arizona.edu/biomath/tutorials/polynomial/graphingpolynomials.html

But I haven't looked into this fully yet, and it sounds like you might
be saying that its not that simple.  I was just looking into regression
equations for the purposes of curve fitting from a number of discrete
doppler offset observations.  At a quick glance, the cubic polynomial
seemed like the right 'shape' for the regression.

I think what you might be warning about is that, in doing so, because
there are a large number of parameters that go into the generation of
the doppler (and its s-curve), that we might be losing necessary
fidelity in the data by assuming a cubic polynomial? Honestly this all
kind of new territory for me, so any and all advice is welcome.

Thanks again for the info, much appreciated.

-Zach, KJ4QLP

Research Associate
Ted & Karyn Hume Center for National Security & Technology
Virginia Polytechnic Institute & State University
Work Phone: 540-231-4174
Cell Phone: 540-808-6305

On 11/9/2015 3:29 PM, Daniel Estévez wrote:
> Dear Bob and Zach,
>
> This paper might be worth looking at:
> http://www.dtic.mil/dtic/tr/fulltext/u2/409103.pdf
>
> As far as I know, it started the whole business of location by
> measurement of Doppler shift.
>
> Apparently, according to the success of project Transit, it is possible to:
>
> a) Compute the TLEs of a satellite by using just a few minutes of the
> Doppler curve of the beacon of a satellite, as received on a ground
> station with known location.
>
> b) Compute the location of a ground station, by using just a few minutes
> of the Doppler curve of the beacon of a satellite with known TLEs, as
> received on said ground station.
>
> Of course, several variation on this are possible, such as the one which
> is discussed here:
>
> Compute the location of a ground station by using the Doppler curve of
> its transmissions during a pass, as received on a satellite with known TLEs.
>
> It seems that the key point in all this is that the Doopler curve
> depends independently on all the parameters in question (so not a cubic
> polynomial, which depends on fewer parameters).
>
> 73,
>
> Dani M0HXM/EA4GPZ.
>
> El 09/11/15 a las 17:59, Zach Leffke escribió:
>> No worries, I thought on it a bit more and I think a cubic polynomial is
>> the right fit.  I also found some python tools for regression
>> calculations that I think will be useful for this.  Also, I think this
>> is pretty similar to how the COSPAS/SARSAT system used to locate lost
>> ships (EPIRBs) and downed Aircraft (ELTs) before the proliferation of
>> GPS and its inclusion in the locator beacons.

```

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