[amsat-bb] Mobile Ops with NO PC.

Bob Bruninga bruninga at usna.edu
Sun Jan 30 08:48:23 PST 2011

> When I first discovered... Satellites,... 
> computers consisted of the trs-80...  The
> Oscar Locator was my computer of choice, and
> worked... well with the ascending node data...

Yes.  Newcommers might not realize that you don't need no stinkin computer to know when satellties are in view.  For AO-51 for example, you only need the peak pass time in the morning and evening for 5 days.  These times are good for the next month or more because they repeat every 5 days.  Example:

My "Post-it" note tracker for Maryland for February:

30Jan |31Jan |01Feb |02Feb |03 Feb|
11:04  10:25  11:24  10:45  10:00 |
                            11:40 |
22:16  21:37  22:36  21:57  21:18 |
                            22:57 |

Since the orbital period is about 100 minutes, you KNOW there is a pass 1 hr adn 40m earlier AND later than the two times per day above.  That gets you 6 passes a day.  The double times in the last column are because there was no single peak pass that day, but two equal elevation middle passes.

Since 4 Feb cycles around to the start again, the way I actually write the above Post-it note for my mobile is as follows.  Note the times are the same, but I changed the dates.  I also added the subtraction of about a minute per day in the overall orbit.

30Jan |05Feb |11Feb |17Feb |23 Feb|
      |  -5  |  -10 | -15  | -20  |
11:04  10:25  11:24  10:45  10:00 |
                            11:40 |
22:16  21:37  22:36  21:57  21:18 |
                            22:57 |

This format increments the 5 day cycle for each column.  This chart works easily for nearly a month without any mental calendar math.  Just look at the column that is the closest date to NOW and then move forward or back 1 or 2 days to the right date.  For better accuracy, subtract the minutes shown for that 5 day cycle.

For 6 Feb for example, start at 05 Feb and count forward 1 day to the center column.  The morning peak pass will be at 11:24 -5 or about 11:19.  Notice how if you keep counting from this 6th around to the 11th, that there is is, the 11th already labeled for you.

This technique is great for long trips or vacations so that no stinkin trackin hardware is needed to operate mobile FM satellite, just the post-it-tracker on the dash board. If you keep track of moving the times earlier by 5 minues every cycle, it lets you know all passes everyday for over a month.  And you can continue guessing beyond that, because if you are actually using the satellite, you can update the times as you go.

DETAILS:  No, the orbit period is not exactly 100 minutes but more like 99.  But since this is all mental math, then 1 hour and 40 minutes is much easier to predict.  So for the next pass time all you really need to do is ADD 40 minutes and then 1 hour.

For the previous pass it is easier to ADD 20 minutes and subtract 2 hours than it is to mentally subtract 100 minutes.

Very quickly you get the hang of it.

The mobile operator with OMNI antenna is ususally only going to be optimum for the high elevation pass anyway, so this really is a neat way to work the satellies anytime you are in the car.  These times are the PEAK elevation times (CENTER of the pass), so get out there 5 minutes before these times).  You can get the pass time peaks from www.heavens-above.com

My web page gives other examples for some other satellites.  GO32 when it was working for APRS packet, was good for several months because the orbit did not precess much.

see: http://aprs.org/MobileLEOtracking.html

I wish I had time to write an AUTOMATIC web page calculator for people so that all they had to do was enter their LAT/LONG and the web page wouild print a post-it-tracker for you.  But I just dont have the time.

It would be a POPULAR site for mobile satllite ops and might actually get more people on the air!  You don't need no stinkin' computer to work satellite mobile!

There are those who will insist that downloading keps to their smartphone is a far better technique, but that ONLY works if you pull it out every time you get in the car and bring up the app and LOOK at it.  For me, looking at the DATE on the post-it note and the TIME printed there is far more likely to be noticed by me.

Bob, Wb4APR

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