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Old 09-16-2016, 10:02 AM
VHS VHS is offline
 
Join Date: Feb 2008
Location: Napa, CA
Posts: 293
Default Digipaths for aircraft

My business partner and I have been kicking around firmware changes for airborne applications. At first, we combined both high altitude balloons and fixed wing aircraft into one mode of thinking, and quickly realized that there are no parallels between the two, with the exception of limiting the digipath above some altitude. Unfortunately, the GPS only knows its altitude above sea level, and it does not store an atlas that keeps track of your AGL.

My thinking is that in general, during most flight, altitude is a function of velocity; if you are going fast, you are most likely flying high, and we could switch to a narrower digipath to keep you from pinging digipeaters out to the geometric horizon and beyond, but use the wider, mobile path for those times you are sitting on the ramp, or hanging upside down in the trees. I know this is imperfect, so I am looking for ideas on how best to upgrade the firmware for typical flight profiles. Of course, we would keep all the configuration options open, and not try to brute-force you into any new and untested ideas.

Other than just for the sake of polite operating, the only real problem I have ever seen with using too wide a digipath at altitude is hitting a bunch more digipeaters and I-gates than you really need to. Even this is not crippling to the APRS network, unless it is combined with sending lots of extra packets. This can happen when using SmartBeaconing and flying aerobatics at high altitudes.

So basically, I am soliciting you for your thoughts on how best to improve performance, while at the same time not incurring the wrath of the secret APRS police for abusive operation.
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  #2  
Old 09-16-2016, 11:19 AM
Lenny Iszak's Avatar
Lenny Iszak Lenny Iszak is offline
 
Join Date: Sep 2008
Location: Palm City, FL
Posts: 261
Default

We could use an MEF database (see https://www.faa.gov/air_traffic/flig...ts/aero_guide/)

The Maximum Elevation Figure (MEF) represents the highest elevation within a quadrant, including terrain and other vertical obstacles (towers, trees, etc.). A quadrant on Sectionals is the area bounded by ticked lines dividing each 30 minutes of latitude and each 30 minutes of longitude. MEF figures are rounded up to the nearest 100' value and the last two digits of the number are not shown.

Not super accurate but it would be a relatively small dataset and it should actually make the tracker operate properly in mountainous areas.

Another idea is with an onboard receiver like your new MTT4B we could listen to the aprs band. If we hear more people transmitting we're probably up high and we should use less power.

Lenny
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