OK,
Kurt's talked me into the RPSMA jack. It looks like Jim has an antenna with a cable that I can just bolt through the aft bulkhead of my AV bay. Now edge or flush. Edge is better I think I recall.
Adrian
I don't know if there is that much difference in real use. First of all, under acceleration the GPS can lose lock because of Doppler effects of the received signal. I thank Keith Packard for pointing that out in a post on TRF. Plus if one looks at
the G limits of the commercial GPS receiver chipsets, most of them are only guaranteed to 4G's acceleration. Doesn't mean they break it means they might break lock momentarily. In addition there is a 1000 knot/ 1200mph speed limit
so a commercial GPS can't be used for a guided rocket with nefarious purposes in mind. Your mach screamer might not get a lock temporarily due to the above phenomena.
Once in the coast phase of the boost, an upward facing GPS has a clear overall shot of the sky. A side facing one still has a good shot of the horizon but whether or not high frequency spinning makes a difference for amateur rocketry purposes
I don't know.
If one gets an upward facing GPS antenna, might be able to get a lock some time before apogee and on descent here's where it may get tricky. If the upward facing antenna is lying horizontally on descent facing the horizon, that still is a pretty good position to get and keep a fair number of satellites locked. If ones descent has the GPS antenna facing the ground, that would be less optimal. Will the GPS keep lock? Maybe and likely but there's a better chance if it were facing the horizon or up to the sky. That's where technically a side facing antenna might have an edge. But then again, both configurations are going to be flopping around on descent anyways. I think that's the reason some Rf positions are missed on descent at the
receiver. Please note, with onboard memory recording the GPS positions written to memory one can miss a bunch of Rf packets but the GPS may still have a lock and dutifully writing the positions to memory for later download.
Found that out when a metallic painted rocket couldn't get the Rf out of the airframe but the Rf attenuation did NOT extend to the GPS receiver. When I belatedly did a download attempt of the Beeline GPS .kml memory file, every darned position was recorded once a second with a 7 to 11 satellite lock!! I was lucky the rocket recovered within sight.
Once the rocket has landed, the side facing GPS antenna might be facing down, up or either side. Now I've taken a Sainsonic AP510 laid it sideways and it keeps a lock pretty well. It has an upward facing GPS antenna so it was
facing sideways for the test. An upward facing GPS antenna of a RTx as opposed to a side mounted one like I've just mentioned will be pointed sideways on the ground unless the nosecone containing a RTx "sticks" the landing and is pointed down. Of course the upward facing GPS receive antenna will be facing sidways over the ground if in a mid-section mounted ebay.
In the reality of amateur rocketry, I don't know if there is that much difference between the two configurations as there are so many variables involved. If one has an idea as to the configuration of their dual deploy rocket as it descends, one configuration might be "better" than another but is it accuracy to the point of absurdity? I don't know. The only way to find out would be to fly two RTx units of upward and side facing GPS antennas in the same
rocket, multiple times and see if it makes a difference. I've flown all my GPS trackers with side mounted antennas and got the rockets back every time except the one that crashed.
My gut feeling me thinks when it comes to "finding the rocket" either configuration will work equally the same. Any comments from anyone better informed on this subject? I'm open to learning if what I mention above is inaccurate
and can be changed. Kurt
East coast problems.
