The beamwidth on 900Mhz I’m told is too narrow to keep a Yagi pointed at a rapidly moving rocket. Also there will be lost positions no matter what due to the Mach lockout and reception can be garbled due to spinning of the rocket and the doppler effect at high subsonic speed can interfere with the GPS signal reception from the satellites.
One thing you can do is get a good omni directional antenna on both the transmitter and receiver.
Linx Technologies is a good place to look:
https://linxtechnologies.com/wp/.
I have found a mag base cell phone mobile antenna good for 900Mhz on ebay I put on the roof of my SUV and it seems to work ok. I haven’t been able to directly compare it with a simple SMA Linx antenna on the LCD receiver though.
Don’t give up on the Yagi thing. Once your rocket is down and more or less stationary, you generally will be able to point the Yagi in the general direction of where the downed rocket is. I‘ve tested the Yagi against a Linx omni directional antenna and the Yagi out performs it. I did a recovery using the Yagi and when I first saw positions coming in, stopped walking and unscrewed the connector and screwed on the omni. The signal disappeared. Put the Yagi back and it started getting positions again. The ground Rf footprint is larger with the Yagi.
The other thing is if one is flying on the Playa, the salts suck up Rf like a sponge so the ground footprint is very small and it’s essential to get that last known position close to where the rocket landed. Out in the open, it’s easier to get a visual on the downed rocket so one has a bit of leeway here as opposed to the Midwest that has more vegetation.
If you switch to the 2 meter or 70cm Amateur radio band then yes, the beamwidth of a Yagi antenna is wide enough to effectively be able to point in the direction of a flying rocket and improve packet reception and decoding.
Consider doing shakedown flights with lower powered motors to see how your setup responds. If it works to your satisfaction, then attempt the 30k’ flight. Especially if you’ve never GPS tracked before. Gremlins can creep in no matter how careful you are. Best of luck. Kurt Savegnago