900 MHz just doesn't propagate well over ground, it's due to the relatively short wavelength. 2.4 GHz is even worse. 70 cm is much better, which is why you don't see 900 MHz being used for RDF... it just doesn't make much sense. The best range is with the 216 MHz Comspec trackers, lower frequency = better ground range for a given amount of power.
Of course, with GPS the ground range is pretty much irrelevant... you only need go get a packet close to the ground, then you're going to pretty much walk up to your rocket. If it drifts a bit or gets blown around, chances are excellent that you'll pick up a ground packet as you get to the original spot.
There is a 1.1 watt $95.00 APRS tracker out there for Ham types on the 2 meter band. In fact there are a few of them but since this is about 900Mhz, I'll leave it at that for respect of the thread. 2 meters is simply not needed for sport fliers
and at the high end with the Multitronix product, 900Mhz has been sufficient for some very extreme altitudes likely due to it's 1 watt 900mhz transmitter. (And premium price) Not going to 100k' routinely? Can look at alternative GPS trackers.
Oh, one other tidbit that might help with recovery. I did testing with an actual launch and tracking situation using a Yagi for the
ground recovery. I had a flight that was totally unseen land 1.66 miles away from me. Once the rocket was down, I proceeded towards the last known packet position with the duck antenna replaced with a 900Mhz 13Dbi Yagi. (Probably Chinese units! We all know their specs are shall we say, exaggerated a bit.) I knew where to point the Yagi from the mapping program I was using. The second I started receiving positions again, I removed the Yagi and replaced it with the simple duck antenna. The signal completely disappeared. Put the cable to the Yagi back on and the signal returned. Bottom line is if one needs to increase the
ground footprint of a 900Mhz tracker, a Yagi on the receive end can help once the rocket is down. Yagi not good in flight due to the narrow beamwidth and hard to point at a moving, perhaps out of sight rocket. In the case for in-flight monitoring besides the duck antenna a patch antenna
can give a modest 6-8Dbi gain increase with a wider beamwidth.
That's a patch antenna for 900Mhz mounted on a pole. Haven't had to use it yet. Was an $18.95 special I couldn't pass up
The only other thing I can think of is having a live mapping situation with the rocket being plotted in real time on a map. For close in sport flying not absolutely necessary but for completely out of sight with long distance recovery, can be very helpful if you arrive at the
last known position and no sight of the rocket or signal from the GPS tracker. Now with reception of positions with the rocket coming in at the lower altitudes, the drift line on your map will give you an accurate drift trend and you just have to follow the trend line until you pick up a signal or see the downed rocket. If one just manually inputs the last known position into a handheld mapping GPS, sure once you get to that position you can "assume" the current wind you are experiencing is what the rocket was
experiencing before touchdown but if the wind had shifted before you got to that spot, could end up going in the wrong direction. All these little details can provide a insurance you get your project back, some of which aren't that pricey to partake of.
There is nothing worse than losing a pricey rocket. Believe me, I've done it with a Beeline GPS but that was a deployment failure in a metallic painted rocket with ballistic recovery. I got the remains back from the landowner 18 months later. No positions at altitude.
Kurt