[DSP-10] More EME-2 tests

[Courtney Duncan]

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