[DSP-10] More EME-2 tests

[Andrew T. Flowers, K0SM]

Incidentally, anyone know what the doppler spreading due to libration 
fading is like at 144 MHz?  I remember talking with K1JT about this 
problem as it relates to using JT65 above 1 GHz.  It seems it could be 
on the order of a Hz or so.  For EME-2 I imagine this isn't too big of a 
deal as most of the energy will fall into the same bin.

-Andy K0SM/2

Courtney Duncan wrote:

> I'm conducting more moon-rise and moon-set EME-2 tests at 30 watts to 
> a 12 element yagi.  I've decided not to invest in an amplifier or 
> elevation rotator just yet (and struck out trying to borrow one, at 
> least so far).  I've decided, rather, to attempt a post-processing 
> program.
>
> This will lead to more questions.  I'll try to figure it all out from 
> the source code, documentation, comments, and inspection, but if I get 
> really stuck I'll post questions here.
>
> This program will allow some editing of the data, deciding to throw 
> away more points for more reasons (good ones or arbitrary ones).  The 
> "noise blank" feature already does this sort of thing.  In post 
> processing, I'll be able to "try things" on the same set of data.
>
> I expect to need maybe a dozen of the hour-long passes I currently get 
> (quiet ones at that).  I have two in the can so far.  :-)
>
> So here's the first question.  As I sit here watching EME-2 slowly 
> make integrations (watching a pot boil....) I sometimes see features 
> develop that seem like they might be something.  Like, five adjacent 
> bins will make a nice little hill, but not necessarily centered at 
> Cntr Sig.
>
> At first I was worried that there might be a Doppler error of a few 
> bins.  Before I continue, let me say that I've decided (after watching 
> several of these pots boil) that I'm just seeing coincidences and they 
> don't represent the signal that I'm looking for beginning to emerge.  
> However, it did get me to wondering how accurate the Doppler 
> calculation is.
>
> I compared to a 90s vintage satellite tracking program (from AMSAT) 
> Instantrack 1.50.  IT's az/el for the moon was exactly the same to 
> 0.01 degree display resolution, as far as I could tell by eyeball 
> synchronizing the clocks.  This means that the two codes agree in 
> moon/station position to a few tens of km.  The Dopplers, however, 
> were different by several Hz, varying from time to time in the month. 
> Right now, for instance, they are 13 Hz different.
>
> I corresponded with one of the maintainers of IT (KB5MU) and learned 
> that IT uses what they call the "truncated Meeus model", that is, the 
> polynomials are truncated to the A + BT or first order terms.  This is 
> for computational speed where amateur-grade pointing accuracy is the 
> only competing requirement.  Your average OSCAR user would think 10-20 
> Hz Doppler accuracy and 0.05 degrees in az/el was great.
>
> So the question is, how accurate is the DSP-10 moon Doppler 
> calculation?  I saw in the documentation that (five years ago) there 
> were errors on the order of 15 parts per billion.  That is about the 
> same size as a bin at 2 meters the way I'm set up right now (323 Hz 
> center) so I would expect to not quite be able to see that.  Is there 
> something about the formulation that might degrade over several 
> years?  (If there's a place in the code that discusses this, just 
> point me to it.)
>
> The reason I ask is that I could put a per pass (or per point for that 
> matter) frequency offset in my program if it would help.
>
> 2.3 Hz at 2 meters is 4.6 meters per second.  Not a bad precision for 
> the three-body problem!
>
> Courtney
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