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Re: AO-40 current ALON/ALAT



Hello Hasan et al

I am sending this from my home e-mail account, I am subscribed from my work 
QTH and so I hope this message is accepted by AMSAT-BB. If after a while you 
do not see this e-mail via the AMSAT-BB, could you post it there please.

 > First of all, the latest version of InstaTrak has it right, the author wrote
 > the correction. The correction is required because the antennas on AO-40 are
 > on the opposite side of the spacecraft that was used for AO-13. This 
requires
 > the addition of 180 deg to ALON and change in sign of ALAT.
 > 
 > Several satellite programs require this "manual conversion" so it's no big
 > deal.

OK, I've modified mtrack, in the section where you enter the ALON and ALAT I 
have added a "-Z" toggle button. It seems to work. So that is out of the way.

 > Second, if it becomes necessary to enter a true negative value for ALAT, 
Doug
 > Cole has said the program doesn't "act right" if you try to enter a negative
 > vlaue for ALAT. That is definitely a bug in mtrack.

Yep, I fixed that a while ago. Although ironically when you do the -ALAT fix 
that you mentioned it stops being a problem :-) It was a data validation 
error.

 > Additionally, in your message to me you indicated you thought that mtrack
 > might be ok....I don't think it is.

I don't have a copy of your private e-mail with me here, but I thought the 
figures were very similar. Sorry for misreading it.

 > If you look at the az/el of the two programs:
 > 
 > mtrack: 70/-25 Range 53588 km
 > IT:     69.9/24.36 Range 53570 km
 > 
 > VERY GOOD AGREEMENT

Thats very pleasing. I went through the code ticking off the variables that 
are used in the calculation of the Az, El and Range and marked them as being 
good. I then went to check the variables used in the squint calculation ...

 > With the position of the bird so close between them, there shouldn't be an
 > error of 3 deg in squint, so something is wrong with the squint calculation
 > in mtrack.

... in the squint calculation I use some of the previously mentioned "good" 
variables, and the values of ALON and ALAT converted to Radians. There are no 
magic constants in the squint calculations that need tweaking, just 
combinations of sin, cos and tan and addition and multiplication. 
Unfortunately finding such a bug requires a mathematician who understands 
geometry and I'm not it.

It is a pity that the difference is not bigger as it would be easier to find, 
but a small difference of a few degrees is difficult to find. It also doesn't 
help that I don't have any other satellite tracking program on my PC for 
comparison purposes.

 > Hopefully, this will help resolve the current and potential future problems
 > with squint and mtrack. Thanks so much for all your efforts with this fine
 > little tracking program. Whenever my 3rd machine is in Linux (which is most
 > of the time), I always have mtrack running.

I am almost ready to release the beta of the new release, but I really need 
someone who can build it from source.

 > 73

... and a Happy Christmas

Jonathan  G4KLX / HB9DRD

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