Using APRS for tracking, needs improvements

[vpatron]

Hi guys,

Any APRS experts here? I figure there's a lot of smart people in this UAV group so I'll ask here.

I finally got the GPS receiver and an APRS modulator on my plane working. It's sending GPS packets over the audio channel of my existing video downlink so I DO NOT need an expensive wireless data modem like the 900 MHz Maxstream.

Take a look at this plot: http://www.nortap.com/AGWTracker

The problem is that I often shoot small subjects and APRS has a limited resolution; they strip the lat/lon to only something like 2 decimal places in minutes. (This was for a roofer who was re-roofing this building at the time.)

The airplane icon will stick in one spot for several seconds, then jump way over to another spot making it difficult to really judge the direction of the plane from the computer screen. Our airplane flies quite slowly and is custom designed to shoot these low, close-in shots.

So a bunch of questions:

1) If I came up with an APRS FSK modulator (I'm using the TinyTrak3 by Byonics.com now) that added more decimal places to lat/lon, do you think AGW Packet Engine will automatically recognize the increased accuracy? I tried email the author and did not get a reply.

2) Any ideas on other ways of getting GPS data over a band-limited audio channel *cheaply*?

The other idea was to get Byon at www.byonics.com to create a mode to simply encode and compress NMEA sentences, and then decode and uncompress NMEA so that it basically becomes a transparent serial link. He's already starting to ship his TinyTrak4 (See http://www.byonics.com/tinytrak4/ )

Any ideas? Thanks guys,

-Vince
www.nortap.com

[poynting]

I'm not sure if you're using a sound card TNC or a hardware TNC for decoding, but if it's the latter, you could try to type a packet formed with the resolution that you want (or copy/paste) into a serial program with a loopback connection to the serial port that AGWTracker is receiving data on, just to see if it'll support the resolution.

You could also email Byon and ask for a version of TT3 code with the resolution you want. He's a nice guy and might do it for a fee if he has the time.

[air]

Just go to newmicros.com and get the following setup:
1 USB Dongle $75 (http://www.newmicros.com/cgi-bin/store/order.cgi?form=prod_detail&part=USB-XBEE-DONGLE&id=3oF3q4j4y16xlTT6YK42X3od76r4Ypg3)
1 Xbee Pro $32
1 XBee Carrier (RS232, 3v or 5v so guaranteed to work with whatever gps you buy!) $16

And there you have it, a tracking solution for just over $100 that will work out to a respectable distance.

If you want more range, just get a USB Dongle Carrier instead, then an XBee with a U-FL socket. Then get a U-FL to RP-SMA pigtail and you can hook it up to a 20db panel antenna if you like ;)
You could also get a U-FL socketed Xbee Pro for the other end and put an omni on that.

The extras listed above shouldnt run you any more than another $100 or so.
With these low cost high performance chipsets available I think APRS has seen its day for our type of application.

[vpatron]

Wow, you guys are awesome! Just a quick reply for now; I'm heading out the door.

poynting, great idea. I will definitely try it! Yes, I've met Byon and he's very nice, but quite busy. I'll do your test on AGWTracker before I bother him.

air, Wow, that's a great price! But I'm sure the signal will get wiped out by my 1 Watt 2.4 GHz video transmitter! I might have to look into 900 MHz video.

Do you know if they have a serial version instead of USB? I'd like it to support sending 5 Hz GPS rates (and those use 38k baud) and if this only supports 9,600 baud, then I'd have to insert a microcontroller at both ends to do compression, strip out unneeded sentences to get 5 Hz into 9600 or 4800 or whatever baud rate it supports.

Thanks! I'll research more later when I get back.

-Vince

[air]

Yeah, theyve got loads of serial (232) carriers on their site, you could just attach a serial cable to one of them and you're golden.
The zigbee modems are capable of much more than 38k so you'd have no problems. You need a full rs232 carrier to program them with the Maxstream XCTU software though (with dtr and cts terminals connected). You should probably buy the RS232 board from Maxstream, I think it's about $80.
Strange that you're worried about 5hz gps rates now and two posts ago you were considering APRS ;)
You'll have to ditch the 2.4ghz video for sure.

[vpatron]

Byon emailed back and said I can configure TinyTrak3 to NMEA instead and it will send 4 decimal places, instead of 2 for MIC-E format. I think this will slow down the rate though.

Hmmm..

-Vince

I'm not sure if you're using a sound card TNC or a hardware TNC for decoding, but if it's the latter, you could try to type a packet formed with the resolution that you want (or copy/paste) into a serial program with a loopback connection to the serial port that AGWTracker is receiving data on, just to see if it'll support the resolution.

You could also email Byon and ask for a version of TT3 code with the resolution you want. He's a nice guy and might do it for a fee if he has the time.

[vpatron]

Ya, I know. I was trying to do it cheap and I thought APRS would be the cheapest, and I could live with 1 or 2 second updates.

But now that these modems are so cheap, hey, why not go for the gold! At 5 Hz rate and our existing altitude hold module, we can practically fly the plane totally on instruments and get it positioned exactly where it should be!

Gosh, now I have to look for a 900 MHz downlink. They're getting rather rare these days, and good ones are even more rare.

-Vince


Yeah, theyve got loads of serial (232) carriers on their site, you could just attach a serial cable to one of them and you're golden.
The zigbee modems are capable of much more than 38k so you'd have no problems. You need a full rs232 carrier to program them with the Maxstream XCTU software though (with dtr and cts terminals connected). You should probably buy the RS232 board from Maxstream, I think it's about $80.
Strange that you're worried about 5hz gps rates now and two posts ago you were considering APRS ;)
You'll have to ditch the 2.4ghz video for sure.