[amsat-bb] Gold Standard for Keplerian Data

[Erich Eichmann]

Steve,
your setting of "minimum elevation" will be the reason of your 
observation. The default setting of "minimum elevation" in WinAOS is 0 
degrees. You should leave that setting or specify only a few degrees if 
there are obstacles around.  As you wrote your setting is 15 degrees. 
With that setting the program does not only skip passes with a lower 
max. elevation but shows only the part of a pass the sat is above 15 
degrees. That makes a difference of 4-5 minutes less transponder time at 
the beginning AND at the end of a pass because the elevation of a 
satellite changes much slowlier at low elevations than at higher ones. 
Many audible passes will not be displayed at all.

The purpose of WinAOS is to give you a quick overview over the audible 
passes of the selected satellites and for this purpose it completely 
sufficient and  very useful (for me since more than 25 years). WinAOS 
uses a simpler orbit model than SatPC32 does (also SatPC32ISS, Wisat32 
and WinListen) which uses the very exact SGP4/SDP4 model. Since WinAOS 
calculates in intervals  of 1 minute the max. elevation may be wrong 
(too low, never too high) by some degrees - with high   elevation the 
angle can change by 15  or more degrees within 1 minute.  But that is 
not important  The rising and setting times are exact within one minute.

For exact predictions you can use WinListen.

73s, Erich, DK1TB





Am 24.11.2014 05:21, schrieb Steve May:
> I appreciate the suggestions. After a long day at work I have sat down this
> evening to look at the system, but I am still stumped.
>
> I am using a Windows 8.1 system, and the clock appears to be synchronized
> correctly. I am letting Windows set it automatically, and when I look at my
> cell phone the two display the same time and the minutes change
> simultaneously.
>
> The Keps seem to be updated correctly, and it shows that they are looking
> at the file that was updated earlier today. I looked in the directory and
> the updated nasa.all file is there.
>
> The time seems to be incorrect for all of the satellites I am trying to
> predict. Since I am only concerned with AO-7, FO-29, AO-73, and SO-50 they
> are the only ones I a running a prediction for, and since I am pretty new a
> this I am trying to use a 15-degree minimum elevation.
>
> I am generating a WinAos list, and it seems to be pretty much across the
> board hat the predictions in the WinAos software are about 5-6 minutes
> later than the predictions from the AMSAT website. Some of the predictions
> show a 1-degree difference in max elevation as well, although it isn't on
> every pass. These inconsistencies are probably based on rounding.
>
> It is showing this difference in time on every satellite in the predictions
> as well.
>
> I have checked and double-checked the Observer location on both predictions
> and I am using the correct location, EM78re. I have tried it on both
> predictions to enter the 6-digit grid square location as well as putting in
> the GPS coordinates manually and it doesn't seem to change anything.
>
> I am stumped by this. I assume it has to be something in my SatPC32 setup,
> and I will try it at work tomorrow on a different machine to see if the
> errors are the same.
>
> Any other suggestions?
>
> Steve, W5IEM
>
>
>
>
>
>
>
> On Sun Nov 23 2014 at 12:45:34 PM Erich Eichmann <erich.eichmann at t-online.de>
> wrote:
>
>> Steve,
>> I compared the results of the pass prediction from the AMSAT website for
>> the next 10 passes of FO-29 with the results of WinListen (that comes
>> with SatPC32) for my location (8.9 degrees east, 51.94 north). The
>> results are exactly the same (WinListen rounds the AOS/LOS times to the
>> closest full minute, however). It requires to enter and save your QTH
>> locator or longitude/latitude.   I used the latest file nasa.all as Keps
>> file.
>>
>> in most cases of different results between the AMSAT pass precition and
>> SatPC32  wrong longitude/latitude values in menu "Setup", "Observer" or
>> "Setup" of WinListen or  different  Keplerian data were the reason.
>>
>> What is your 6-digit QTH locator (or longitude west and latitude
>> north)?  What is the entry in SatPC32, menu "Observer" and in WinListen,
>> menu "Setup"?
>>    What Keps file do you use?  Download  the Keps file you use from
>> SatPC32 menu "Satellites", "Update Keps". When the download is
>> successful click "Quit" and then "OK". The path to the Keps files folder
>> can be seen in the foot line of menu "Satellites", the file date in the
>> bottom line of the SatPC32 main window and in the left list of the menu
>> you can choose the file. WinListen will use the same same path (foot
>> line in menu "Listen").
>>
>> 73, Erich, DK1TB
>>
>> Am 23.11.2014 17:04, schrieb Steve May:
>>> I have noticed that when I update the Keplerian Data for my location on
>>> SatPC32 and generate a list of passes they all seem to be about 5 minutes
>>> different than the predictions from the AMSAT website. This is for the
>>> earliest pass, and I am using the exact GPS coordinates for my location.
>>>
>>> So which do I rely on? Which predictions should I consider the "gold
>>> standard" for passes?
>>>
>>> Steve, W5IEM
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> _______________________________________________
> Sent via AMSAT-BB at amsat.org. AMSAT-NA makes this open forum available
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