On Wed, Dec 23, 2009 at 7:34 AM, Peter Howell <[email protected]> wrote:
Hey Keith, Pete's callsign is KD0CVN-1 > I have the a Nuvi350/tracker2/Yaesu mobile setup running in my > experimental airplane. It works great - super tracking - easily > updated status messages, and the envy of my flying friends - > the email from 10,000 ft! It looks like you might have done some homework... From what I can see, you are using a single hop path at most. As you have observed, you can get into the APRS network from an airborne platform very nicely. As you are probably aware, in the realm of VHF communications, antenna height is where it's at. When you are flying, you have some of the best antenna height available. Running long paths, or very fast beacon rates from an airborne platform can cause a lot of problems across the APRS RF network. With just 500 feet AGL, you're probably going to get into a LOT of digipeaters for many miles around. The APRS-RF network can handle getting hit like that, but it's all your earth bound neighbors that might feel a little miffed by you hogging the network. > I'd like to set up the digi function(mini awacs), but I am not well > versed in how to set up the parameters. Is there a good guide I > can access? The tracker2 manual makes it seem too easy - > maybe it is. Okay, so... remember how you can hit a whole bunch of digipeaters from 500 feet AGL? Well, the reverse is true as well, but it's not only the digipeaters on the ground that you can hear, but every other station on the ground. If you run an airborne digipeater that acts like a ground based digipeater, you're going to be causing quite a bit of noise. Every ground based station asking for a hop from a digipeater will not only bounce through the regular digipeater network, but will also be handled by your airborne digipeater. You'll be adding to the noise factor in areas already covered by digipeaters. Also, due to your altitude, you will be increasing network loads because you will be causing stations located well outside the ground based digipeater footprint to be included in the local digipeater network. Think of it this way, if you can hear a station 200 miles away, and you digipeat him, another digipeater 200 miles the other direction will most likely hear your digipeated packet. That means that the original station which is 400 miles away from the ground based digipeater is now effectively a local station, and will be seen in that area. Now multiply that by a couple hundred times, to include all the ground based stations you'll be able to hear... and you thought that the earth bound peons were grumpy when it was just you making noise from the sky... To get an idea of what traffic you might be bouncing around the local RF network, try this... Go to the page linked below. http://aprs.fi/?call=kd0cvn-1&mt=m&z=7&timerange=3600 This will show the last hour of packets from your station, from the last time you were up flying. Now without touching anything else, click on "Show All" in the upper right side of the screen where it says Track Callsign: [Clear / Show All] Hold on for a bit, and watch all the stations that you could potentially be digipeating show up on the map. That's quite a few stations, and an awful lot of airtime being used. Now, if you were flying around Saskatoon, Saskatchewan, things might be a bit different. http://aprs.fi/?call=VE5RHF&mt=m&z=7&timerange=3600 Again click on the "Show All" link, and you'll see why you wouldn't cause such grief. You can still run an airborne digipeater, as Bob by running it on a frequency other than 144.390. If there is an alternate experimental APRS frequency in your area, an airborne digipeater might be welcomed as an interesting adjunct to the network. The other option is to run a non-standard digipeater alias. Digipeating on just your callsign, or an alias such as TEMPn-N would not cause problems, as the ground based stations would need to specify using your airborne digipeater explicitly. Yes, we are indeed raining on your parade. Think of it this way though. Would you drag a VHF repeater up in the plane on 146.85 and run it while flying? Of course not, you would interfere with the repeater on the east side of St. Paul, and probably a couple others depending upon how high you were flying. The APRS network runs on a single frequency, and there are literally thousands of people using that resource. While amateur radio is experimental by nature, we already know what the results of these types of experiments will produce. Now, if you have a special event of some kind that could benefit from having a long range digipeater available, feel free to fly one, but just be aware of the issues outlined above. Set up a sked with some buddies that are far flung, get the plane up at 9000 feet, and see if they can bounce signals through you using a special digipeater alias. You can still play and have fun, but you're not going to drag everyone else in the world into the fray. I hope this makes sense to you, and gives some reasoning behind why you would NOT want a flying digipeater on 144.390 acting upon WIDEn-N packets. Maybe a little easier to live with than just getting your fingers slapped and told NO! James VE6SRV
