What's everyone using for rotor cable to feed the Alpha Spid?
Ryan, NF0T
On Wed, Jun 3, 2020 at 1:45 PM Leffke, Zachary via AMSAT-BB < amsat-bb@amsat.org> wrote:
Hi Dave, We use a lot of the RAS/HR and Big-RAS/HRs at VT in our ground station and on other projects. My biggest recommendation is if you don't absolutely need the resolution, don't get the high resolution variants (0.2 deg resolution). It uses a quadrature encoder feedback mechanism that is highly susceptible to EMI corruption leading to 'dropped counts' and a general slew of problems related to calibration and reliable pointing knowledge. We have constantly battled this problem since day 1 of the VTGS and still don't have reliable resolution for the problem (but enough band-aid solutions to keep limping along and periodic trips out to the tracking station to recalibrate). The smaller Ras/HRs seem to generally do better on the feedback front (still high resolution with the quadrature feedback) for some reason, but we typically use those in 'deployable' scenarios and the feedback cabling is much shorter (maybe 20ft or so)....so not necessarily an apples to apples comparison with the perm anently installed Big-RAS/HRs that have longer feedback cables (roughly 100-200 ft depending on which antenna stack we're talking about) and generaly seem to be more prone to issues. I also personally own a Ras/HR (smaller one) with the high res feedback and a 2.4m solid dish mounted on it. It can handle the load just fine with proper counterweighting and so far I haven't had any feedback issues (roughly 50ft feedback cable)....knock on wood.
The 'non high resolution' (low resolution?...its still accurate to about 1 deg) variants use plain ol' potentiometer feedback. I don't have direct experience with them, but have reports from some colleagues that they haven't had any serious or repetitive issues with pointing calibration (some radio astronomers in Physics dept are using one with a 2m dish). (I think that one uses a different controller than the MD-01 that we use, but I think the MD-01 or MD-02 could handle either type of feedback).
Other 'warnings' include realizing they have no mechanical stops in azimuth (they do in elevation, roughly at 180 deg limits). That said, it isn't really a problem as most controllers work reliably with 'software limits' and the MD-01s at least have timeouts that help if things 'go wonky' with feedback. There are some cases though that result in the perfect storm of corrupted feedback that goes undetected by the MD-01 that could lead to a bad azimuth situation; in our case we monitor antenna motion on a camera, so are able to mitigate that scenario with human intervention (and our custom control software looks for 'impossible speeds' as reported by the MD-01 positions that further helps mitigate that when the feedback goes awry).
Mechanically, they have done very well for us with the double-worm gear design, imperceptible gear slip (if any). I've heard of folks having mechanical failures, but I don't know the details, and that hasn't been my experience. As an example, at the height of 'performance' I was able to reliably track multiple S-Band downlinks with a 3m mesh dish antenna with no discernible negative effects due to point errors or 'jiggle' in the system (part of that is the ramp up, also part the counterweighting). In the 5 or so years we've been running them, we haven't had any major mechanical malfunctions (knock on wood), and part of that is probably due to periodic maintenance (re-greasing and such), which I've done at least once (can't remember exactly, maybe twice in that 5 year window). Part of that is also the fact that we tend to use the yagi stacks with a lighter load a lot more than the larger dish systems, I might be singing a different tune if the dishes were used daily.
The MD-01 controller (and MD-02s as well for non-rackmount variants) does have some nice ramp-up/ramp-down features, particularly useful for larger systems (like our 4.5m dish). I do wish the API documentation for the MD-01 command interface was a little better...but we've been able to work through it (for example, they changed the protocol a bit in a relatively recent firmware update that broke compatibility with our software and presumably things like rotctl in hamlib, but I think that has all been fixed/updated). The API issue might not be a problem for most folks not interested in writing their own software, or if you are using a different controller. The overall documentation situation is a little 'meh' in general as there have been a lot of versions and such released and they are on different websites run by different folks.....but at least there is documentation at all and a little reading and experimentation is usually enough to get what you need, and the basics such as th e wiring diagram hasn't really changed over the years.
I can't directly speak to the SatPC32 question because we don't use it. Other than that firmware update hiccup, I'd be willing to bet it works fine.
Bottom Line: When they work, they seem to work well, at least in my experience. If I were going to buy one today for personal use, I'd get one with the potentiometer feedback if the intended use is for something like a few Yagis and if I were planning a more permanent installation. If I were going to buy something for VT/work with a better funding source than my 'hobby budget' I'd probably look for something better, like M2 products (pretty significant jump in price point though).
I hope this helps. -Zach, KJ4QLP
-- Research Associate Aerospace & Ocean Systems Lab Ted & Karyn Hume Center for National Security & Technology Virginia Polytechnic Institute & State University Work Phone: 540-231-4174 Cell Phone: 540-808-6305
-----Original Message----- From: AMSAT-BB amsat-bb-bounces@amsat.org On Behalf Of Dave via AMSAT-BB Sent: Wednesday, June 3, 2020 1:20 PM To: AMSAT BB amsat-bb@amsat.org Subject: [amsat-bb] Alpha Spid Rotator
Is anyone using an Alpha Spid az/el rotor? If so how do you like it? Would you recommend it over the Yaesu's and are there any issues using it with SatPC32?
Thanks,
Dave N2OA _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb _______________________________________________ Sent via AMSAT-BB@amsat.org. AMSAT-NA makes this open forum available to all interested persons worldwide without requiring membership. Opinions expressed are solely those of the author, and do not reflect the official views of AMSAT-NA. Not an AMSAT-NA member? Join now to support the amateur satellite program! Subscription settings: https://www.amsat.org/mailman/listinfo/amsat-bb