A quick update on the Ublox M9N. I haven't been able to test its upper limits (that will be a long ways off), but I did swap out my Ublox M8N for the M9N on a flight this weekend. To keep it "apples to apples" I used the same patch antenna I have been using with the M8N and I am logging locally to SD card every two seconds. Overall, the M9N performed slightly better, but it didn't blow my socks off. Here is a summary of the comparison between two flights with the same profile:
Flight: A 4" rocket launched to about 15K feet with a 4 second motor burn time (7700 N-sec), max speed of 1,250 Mph (1833 fps), max gee force of 23 G's, and 30 seconds to apogee.
Both GPS units consistently track a solid 12 satellites, while waiting on the pad, but both lose GPS shortly after take-off.
M8N: The M8N loses GPS immediately after launch and regains it about 28 seconds later with 4 satellites, two seconds before apogee. It takes a full 42 seconds of descent (avg 75 fps) to get back to a full 12 satellites.
M9N: The M9N held on to reception longer following launch (about 6 seconds) and reported 2D coordinates with only 3 satellites, but then also lost reception. It came back online 10 seconds before apogee (with 4 satellites), a full 8 seconds earlier than the M8N. Following apogee, it only took 10 seconds for the M9N to regain the full 12 satellites.
So, with the sample of one, the M9N seemed to perform better than its predecessor, but it still drops out during the high speed portion of the flight. I'll keep flying with the M9N and see if the trend continues.
I’ve been off the grid for awhile on this but holee cow Mike, this is incredibly helpful to me and others. I was aware of the loss of GPS reception due to speed limitations and thought Rf reception issues were a big deal.
I think your data might suggest if the rocket is changing geometry quickly (spinning or tumbling) it makes it a bit more difficult for the GPS to get a lock in some of the latter phases of flight. Once it settles down under drogue or main, a better lock can be had.
This is exactly what I’ve seen with even much lower altitude flights. Loss on ascent and then a variable re-acquisition of signal on descent. Sometimes seems like a long wait to me. Nonetheless, enough positions are received to find the rocket. Never lost one with GPS tracking except with a core sample. In that case the metallic paint inhibited the Rf from getting out. Was my first flight. Got the remains back a year later. A later core sample got one position out before impact and that’s where the fincan was found sticking out of the ground. New nosecone, new tracker and the rocket still flies. (Was fiberglass rocket)
Will have to keep the M9N in mind for possible modifications for trackers in the future.
I have some AP510’s
https://www.ebay.com/itm/AVRT5-APRS...507521?hash=item4220e1c141:g:LgsAAOSwzkld1XJV
I’ve been itching to fly and yes it‘s on the Ham band but can be switched from 500mW to 1 watt power.
Only issue is since it’s APRS the best refresh/transmit rate is once every 5 seconds. Not a problem with the intention of recovering the rocket but not ideal if one would like to have a live data stream with the recovery of as much data as possible. With a bit more Rf output, it helps with reception at a distance. Also Yagi antennas on the 2 meter band have a wider bandwidth so it is easier to point the Yagi in the general direction of the rocket. Even on the 70cm band (400Mhz) a Yagi is easy to point and can give a more reliable downlink at a distance.
The 900Mhz, 100mW trackers do have their limitations and I wouldn’t recommend that one primarily depend on them for extreme high altitude flights. For sport fliers (like me most of the time) they’re fine. The Multitronix Kate can put out 1 watt on 900 Mhz hence the exceptional performance that is seen.
Your research shows some of the limits and will allow others to stop chasing zebras with data recovery.
Did some live map tracking with APRS and the NMEA one position per second trackers. Especially if one has a photo map program it’s incredible to see the tracked rocket positioned on a map while in flight. Using APRS and the Linux program Xastir, there will be a rocket icon shown with a bubble that shows bearing to, GPS altitude and horizontal speed right next to the icon in live real time flight! Can record the flight for later replay in real time. Is that cool or what?
Once one’s really high flying rocket disappears on ascent, might as well watch the laptop screen for the first incoming position packet to be plotted. We’re talking soo high that the apogee/drogue event/smoke can’t be seen from the ground.
It got to the point where dual boot Windows/Android tablets were coming out of China. I took a chance and snapped up two different ones that had an onboard GPS chipset in them. They were hard to find. They work. Can do Windows tracking programs or boot to Android and use the GPS rocket tracker program. I have the devices connected to an outboard battery as the computing burden has a significant drain on the onboard battery. With onboard GPS, I don’t have to dink with connecting up an outboard GPS to the tablet to get the local position when proceeding to the downed rocket. That helps a lot although some of the outboard B/T GPS units I’ve tested on plain windows laptops have their own battery supply. No big deal as like mentioned, I just plug in a larger battery and carry the shebang in a one handed box.
If one gets beyond a bearing arrow and distance, it’s pretty neat to track on a live map with the ability to store the flight for later plotting.
Kurt