I am planning on getting my HAM Technician license soon (but we all know that's a relative term) and purchasing a 70cm Beeline GPS transmitter to use alongside my existing BRB900 setup.
Currently debating the 16mW vs. 100mW versions - according to Greg, the ranges of both are 60K and 250K, respectively. I've inquired with a few friends of mine and the general consensus so far is to go with the higher-power 100mW.
Then for a receiver, the Kenwood TH-D72 seems like a good choice, though a bit spendy, as it has a built-in TNC decoder. (Also recommended to me by Greg.)
Now soliciting feedback...
How far do you expect your rockets to fly and where are you going to mount the tracker?
As far as being courteous on the bands, if 70cm is busy in your area then by all means you could dial back but
I don't find it an issue whatsoever. I've been bit by Rf messing with deployment altimeters and witnessed others
who had the same problems.
If you're a sport flier, 100mW is overkill but it will give you a larger ground footprint once your rocket is down.
It's the last received packet above the ground that's going to get you to the general area and you'll likely get a
position packet as you approach the "ground footprint" of the tracker. You expect your rocket to land more than
a mile and a half from you with a lot of rocket eating ground vegetation? Higher power and an onboard beeper is
suggested or you could use the Yagi for the tracking and descent. Kinda of a pain to be swinging a Yagi but for my
rockets, I've used low power and a duck antenna on my D72 and have had no problems with the rockets that land within 2 miles of me. Talk to Greg Clark and he'll tell you he just uses a duck antenna with GPS tracking. I have yet to fly my 100mW BLGPS yet because I haven't had the need to or the flight profile that would necessitate it.
16mW can ride along in the ebay many times without trouble or interference next to the deployment electronics.
Get a used blue cased Garmin Legend, or 60Cs or 60CsX mapping GPS and with the appropriate cable, you can pipe the rocket waypoint to the Garmin and have a position on a map. Tell/lock the unit to "navigate to" while the rocket is on the pad and it will continuously calculate a heading solution in real time while the rocket is in flight. You can scroll from the map to the Heading Display Indicator and follow the course line and the Garmin will tell you your ETA to your rockets last known packet. By then, unless the rocket was really far away from you when you received the last packet, you'll get a final position.
One tip is when walking or driving to the rockets last known position, open the squelch on your D72A. You just might
hear the faint squawking of the tracker at a distance that indicates to you it is still functioning. The TNC is likely not able to decode such a weak signal but it is reassuring that once you get closer, a new packet will arrive with the final
resting place.
Mock up your installation in the rocket, attach bare, contained ematches in canisters and turn everything on. If the altimeters don't cycle or the ematches don't mysteriously pop in 30 to 60 minutes, you're in a good position of having a nominal flight. No guarantees of course but it's better to find out in a test than have the charges blow on the pad or not blow at all with the resultant ballistic flight. The low powered BLGPS units do better than the the higher powered ones with this and some deployment devices are more resistant to being bunged up by Rf than others. Nosecone mounting to put distance between the tracker antenna and the electronics helps.
The P6K, Adept 22's and the Entacore AIM 2 I've seen problems with Rf. I will credit Entacore as they place a caution in their manual concerning that. I use mine with lower fliers I don't need Rf tracking.
Use a laptop to track? PITA. Use only if you are familiar with the software and want to record the flight. To much trouble to depend upon for recovery. One needs a portable handheld solution to go after the rocket. If the tablets shrink smaller then a full featured tracking program might become viable.
Comments: APRS is a once every 5 second transmission of the position. Don't expect any GPS tracker to give you packets while under acceleration period. Also the vagaries of reception and propagation will result in missed packets. You might find yourself sweating a bit once the button is pushed and you don't see anything. The packets will start just before, during or most definitely after apogee and throughout the descent once every 5 seconds.
Add the starting field elevation to your selected main deployment and you can tell when the main is supposed to blow. I have my D72 set to the altitude reading as I also have it connected to a mapping GPS. I don't need the 72 to show me position and distance because I have that on the Garmin. I want to see the altitude. I can tell it's under drogue by the descent rate and when the main blows, it really slows down. This is very helpful especially for totally sight unseen flights. I've had a Wildman Jr. make more sight unseen flights than
flights where the events were seen. One landed .7 miles away and nothing was seen, yet
the main was out and the rocket was fine when I walked up to it.
The BLGPS can store positions as fast as 1/sec for later download for a .kml file one can display on google earth.
Other tracking solutions like the EggFinder GPS transmits the raw NMEA position packet code
1/sec like it's a USB GPS receiver attached to the laptop. Higher resolution but no onboard memory. Using Xastir as a tracking program and a script to spoof the program into thinking the incoming NMEA data is an APRS packet, the increased resolution is quite apparent. But again, a laptop as the sole tracking receiving station is a PITA. Soooo...... Have fun and
you'll be a lot more confident when your rocket goes completely sight unseen.
Kurt Savegnago
