OBSERVATIONS FROM NORWAY. 21 Jan 2006. AO-7 MODE-CHANGES. For those that requested more information on AO-7’s mode changes and the 24 hour timer that controls this change. On page 6 of the December 1974 Amsat newsletter the timer is described thus ... **The 24 hour timer is derived from a 3.181457Mhz crystal followed by 39 divide by 2 counters** (you can do the math yourself.....LA2QAA). However, after having been in contact With Jan King W3GEY ... (now VK3GEY) ... whom was the project manager for AO-7 and helped design and build the satellite ... (together with Karl Meinzer DJ4ZC, among others) ... in his garage 30 odd years ago, I have been given the following information. (Those satellite enthusiasts who don't recognise those callsigns ought to be lined up against a wall and shot!). **The timer uses a simple CD4001AD RC oscillator comprising 1 x capacitor and 1 x resistor** Not particularly accurate but then it was never meant to be. Space (pun intentional) was at a premium and the priority was on the actual RF transponders ... because even under testing on the ground there was a mode-B command RX desense problem ... which was never fixed. What must be remembered here is that this was before the days of the NE555 timers ... (not that they're particularly accurate either) ... buffered CMOS and rad-hardened chips were not available in those days ... just imagine the radiation dose AO-7 has experienced in the last 31 years in its 1400Kms orbit. The CD4001 RC oscillator was followed by 22 divider stages. Karl Meinzer felt that accuracy wasn't that important ... which it wasn't ...the emphasis was on low power consumption. Naturally, such a circuit was prone to drift but even that wasn't particularly important either ... and anyway, who would have expected it to perform in a space environment more than 30 years! later ... (ok, so it hibernated for 20 years). The general idea of the clock ... which is parameter 2C in the beacon telemetry ... was ... no, *is* to increment until it reached 96 ...this can be seen by the telemetry 2C parameter changing every 15 minutes ... ( ok!, pencils out ...how many 15 minute periods are there in 24 hours?) ... then when it reached 96 it would trip the circuit that would change the mode from A to B ... (or vice-versa) ... reset, and start counting again. Amazingly!, 34 years later, while AO-7 is out of eclipse, the counter is still clocking up the milage. Unfortunately, the beacon is not as healthy as it once was due to lack of power ... ("Gators" take note!) ... so copying the telemetry is still quite a random affair, even though to all intents and purposes the transponders are functioning ... this, despite the extreme accumulated radiation dose that is most certainly *not* good for the solar arrays or onboard electronics. However, the sun angle is still good so there's no reason why AO-7 shouldn't prove many more years of communication possibilities ... providing we all use a bit of common sense and follow the recommended operating proceedures outlined on the AO-7 RESOURCE PAGE. This page, and "everything you need to know" about operating AO-7 can be found at ... The current mode changes ... (between A, B and C) ... occur between 08:30 and 09:00 UTC daily. This *may* or *may* not change back to "random" after the spring of 2006. If you can't hear (or copy) the telemetry just check the AO-7 log page for the current mode. 73 LA2QAA & GM1SXX With Thanks to Jan King for being so patient and answering our many questions.