New Product Announcement: GPS
My apologies to Robert and Marshall for the original post accidentally getting deleted. Was trying to merge some topics and they both disappeared. confusedd
Here is the video, please get the thread and questions going again.
https://vimeo.com/129807173
How long will battery life be?
Engineering: Trade offs and choices
Engineering is generally about making compromises to try and best fit the task with the available technology. "You can have all you want of everything all the time" is generally restricted to politicians making campaign speeches.
The GPS satellite system is a download only data path. Acquiring the GPS position at the tag is essentially trivial. The problem comes in how you transfer the data from the tag on the raptor to the receiver at the falconer.
At this point there are two uses under discussion for a GPS locator tag.
The traditional use is long distance recovery. In Europe this is well suited to cell phone based links. You get a location on the hawk any time both the hawk and the falconer have coverage, which in Europe is almost everywhere.Cell phone coverage at both ends of everywhere is not true for North America. Lag times of a minute or two while text/SMS messages are exchanged are no real problem. Real time via a "phone call" format is possible, but "talk time" eats the battery in a hurry.
The new use of GPS locating is as a convenience/flight management tool. A direct radio link from the tag to the receiver is the better choice for real time data. The range limitation (per MRT about 3 miles down and dirty, 15 miles line of sight) is a trade off for data with a lag time in seconds rather than minutes. Battery drain for direct radio link data is moderate compared to cell phone talk time. For a given power level data can not be transmitted as far as a simple radio beep. Per Ron Clarke's question all the problems of signal being blocked or lost continue. Reflections become a non-issue. The hawk's location is contained in the data, the receiver does not care what direction the signal came from.
On the various GPS websites long distance recovery is given it's due. The "buzz" is about the convenience feature.
Marshall has chosen to go with a direct radio link, which is better suited to the convenience mode and possibly better suited to North America. They have chosen a primary battery, which is lighter than a rechargeable battery. They have chosen a smaller battery, accepting a 3 day run time as the trade off. They are the first to break the 10 gram barrier. They have included the old time radio beep, so that when the signal path becomes too long to move data you still have your ears as a back up plan.
It is up to you to decide if their choices fit your uses.
Extended range on direct radio link for GPS tags
With a direct radio link on a GPS tag you are in the same situation as with a simple beeper, except that the same power at the transmitter gets 1/2 to 1/3 the range. All the same tactics to receive a weak signal still apply.
1. Get the receive antenna up.
A. Stand on the top of your truck and hold the receiver up.
B. Better yet add a broom pole or a couple 5 foot sections of PVC pipe.
C. Since the Marshal link receiver is a stand alone device you can put it on a pole or even hang it from your balloon or kite or haul it aloft with your quadcopter (within the limits of of the range of the Bluetooth to download to your iOS device).
D. Take the high ground. Head for the nearest or highest hill. Climb a stack of hay bales if that is the best available.
E. Rent an airplane.
2. Use a stronger receive antenna. there is no reason you can not feed your link receiver from your Yagi antenna, with resulting improved range.
3. You will get the beeper after you have lost the data link. As suggested below follow the beeper until your data link picks up another fix. A spare Yagi or Quad directional antenna would allow maximum range on both at once. Means to get your receive antennas as high above ground as practical still apply.