Bdale Garbee <[email protected]> writes: > Geoff Hendrick <[email protected]> writes: > >> I saved this comment a while ago but cant remember where i saw it: >> "Tests performed at Altus Metrum have shown that a 3-element yagi antenna >> yields good telemetry from rockets to 20 Km (65,600 feet) altitude, and >> that a 11-element yagi antenna can receive telemetry from the TeleMetrum to >> around 100 Km (62 miles)" > > These numbers were extrapolated from signal strength measurements on > actual flights. The highest actual flight I'm aware of so far that > we've got in our flight database was Adrian Adamson's L single-motor > record shot which went to something over 31k feet AGL. The recorded > telemetry file shows good reception through apogee. I'm not sure what > the ground station antenna was, but I'd guess a 5-element Arrow yagi.
Yes, I used a 5-element Arrow yagi to track his flight. I tracked it down within 60m of the ground, at about 3.2km north of the flight line; at that point, it descended behind the RVs parked at the launch. One funny thing about that flight was that the RSSI didn't appear to change much during the whole flight. During ascent, telemetry disappeared until apogee. Adrian generally builds out of CF with the antenna only visible after separation, so this didn't surprise me, although I do like to be able to find the spot when a shovel is the approved recovery tool. During descent, RSSI varied between -85 and -96dBm, with almost all packets being received successfully. I'll note that Adrian is flying version 0.9 firmware, which uses a much longer packet than we use today (94 bytes instead of 32 bytes), which could increase the error rate by some amount. Here's a plot of RSSI and height during the flight:
pgpY8IxdRJyFG.pgp
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adrian.pdf
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Given that success, I'd say we'd easily receive most of the packets from 35k', assuming a similar antenna configuration, especially the newer 32-byte telemetry format. -keith
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