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deej(at)deej.net
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 Posted: Tue Nov 04, 2008 8:50 am Post subject: APRS for aircraft? |
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Dale Rogers wrote:
| Quote: |
If you are using the system, you might want to find out who's
operating the repeater you use the most and donate a few bucks to help
defray the costs of keeping it on the air.
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Or put up an APRS ground based system of your own to help expand the
network. I'll be putting one up in my area at my house at some point.
It is not terribly expensive to do so - an old PC, some free software, a
cheap ham radio (or even an old scanner) and an external antenna.
Here is some more detailed information on how to do so:
<http://www.vansairforce.com/community/showthread.php?t=30180>
-Dj
--
Dj Merrill - N1JOV
Glastar Sportsman 2+2 Builder #7118 N421DJ KR-2 Builder N770DJ
http://deej.net/sportsman/ http://deej.net/kr-2/
"Many things that are unexplainable happen during the construction of an
airplane." --Dave Prizio, 30 Aug 2005
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mprather(at)spro.net
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| Posted: Tue Nov 04, 2008 9:02 am Post subject: APRS for aircraft? |
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I have to think APRS is worlds better than a 121.5 ELT. It doesn't have
to be perfect for it to be worthy of implementing - just markedly better.
I think EPIRB's and APRS should be proposed as an Alternate Means Of
Compliance for the ELT requirements - at least in amateur built aircraft.
If you can demonstrate that you will use a different and largely superior
system, the feds should be happy with that. I realize it may tend to
create administrative/regulatory headaches.. Too bad. 
Regards,
Matt-
| Quote: | Nevertheless, APRS works well airborne for those of us who actually use
it.
-Bill B
On Mon, Nov 3, 2008 at 5:54 PM, rampil <ira.rampil(at)gmail.com> wrote:
>
>
> Having been an advanced class "ham" in high school, I too think
> this is a great idea but not ready for prime time.
>
> Several people mentioned already that you need an amateur radio
> license to transmit on 2 meters. The FCC wasn't too fond of one way
> data streams either, last time I checked (long ago).
>
> The signal is really just line of sight 95% of the time so in NYC, you
> are covered at any altitude, but where there is low ham population
> density and high terrain, you could only expect it to work above
> typical VFR altitudes. The repeaters tend to be built on the highest
> peaks where electricity is available (one way or another) and
> enough hams on 2 m to foot the bill. BTW 432Mhz is also popular for
> repeaters.
>
> --------
> Ira N224XS
>
>
> Read this topic online here:
>
> http://forums.matronics.com/viewtopic.php?p 12155#212155
>
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rv-9a-online(at)telus.net
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| Posted: Tue Nov 04, 2008 9:51 am Post subject: APRS for aircraft? |
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I'd like to address some things related to APRS.
If we treat APRS as a technology trial, it becomes pretty clear what the limitations and advantages are. In my long career in high tech, I found that the probability of success of a new technology was more positively related to low cost than technical perfection. In that spirit, I think some type of APRS has tremendous potential.
Here's my model:
Based on the proven amateur-radio developed APRS, we could build an infrastructure as follows:
1) The FCC/FAA (or equivalents) allocate a discreet VHF frequency in the aviation comm or nav bands for APRS tracking.
2) This frequency must be able to run FM (rather than the normal AM) so that APRS will work as proven in the VHF Ham band. FM is essential to the broadcast nature of APRS because it exhibits what's called "capture effect" in which the strongest signal at the receiver is decoded and others are rejected. This is like the "cocktail-party" effect. When you are talking in normal voices in small groups, you can hear each other, and you brain blocks out all of the other conversations around you. Contrast this with the "frat party" effect where everyone is shouting and nobody can hear. This approach also works better with low-power transmitters, not the 8 or 10 watt blasters that some people fly with--- no need to shout in small groups!
3) This also takes care of the transmit-only problem. Many Hams think that it's unethical to transmit before listening on a radio band. In general, this is true, but for low-power FM APRS the opposite is true. If all APRS stations listened before talking, they would all eventually end up in a deadlock situation where they all transmit at the same time! Think of a rule at a very large frat party where only one person is allowed to talk at once. Everyone else is waiting for the speaker to finish before jumping in with their full-power transmissions... they'd all synchronize to shouting at the same time, even though they think it's ok to talk! APRS has a line of sight range of hundreds of miles, so you can see the problem with waiting for a quiet time to talk, even if you only need to reach the digipeater 5 miles away.
4) Equip all existing VHF groundstations (Comm and Nav) with APRS digital repeaters and/or internate gateways (digipeaters, igates). Very economical. Have the FAA or equivalent run a website like www.aprs.fi .
5) Encourage digital repeaters (digipeaters) to be installed in aircraft rather than just position transmitters. Perhaps mandate (encourage?) commercial aircraft first. Now you have a constellation of aircraft overhead listening to APRS position reports and relaying them potentially thousands of miles. (BTW there is already an amateur APRS digipeater in orbit). This should take care of the spotty coverage at low altitudes or mountainous terrain. Combined with (4), we have a redundant distributed (and cheap) system that is extremely fault tolerant.
The downside of the above is that it requires new hardware in aircraft. OK for amateur builts, but nothing is cheap for certified aircraft. With ADS-B coming, some may ask why? I go back to my first statement... make it cheap enough and it will become good enough! A transmit-only device can be made very cheaply (mine cost $100.00). A digipeater will be more expensive ($200.00?). Installation costs are more expensive than the hardware. Make it common and it will be eventually built into VHF comms. Think of an SL-40 (already has a GPS input), internally modified to transmit APRS packets when not being used for voice R/T. Installation now becomes a box swap.
I've oversimplified this, of course, but my point is that this technology is very powerful, intrinsically reliable and fault tolerant and cheap. Even with the FAA involved (add some zeros to my costs), there is a rational deployment scenario where coverage improves over time. Eventually, if all aircraft have it, it can be used for traffic awareness, but that's another topic.
All of this started because of the ELT debate, but APRS (for that matter, SPOT) has other benefits than just finding crumpled metal.
Vern Little
Vx Aviation
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