From zanchey at ucc.gu.uwa.edu.au Thu Oct 7 11:59:00 2010 From: zanchey at ucc.gu.uwa.edu.au (David Adam) Date: Thu, 7 Oct 2010 11:59:00 +0800 (WST) Subject: [RadioTelescope] beaten to the punch? Message-ID: http://www.icrar.org/news/news_items/new_telescope_puts_focus_on_high_school_discoveries [DAA] From harrymc at decisions-and-designs.com.au Mon Oct 11 08:37:30 2010 From: harrymc at decisions-and-designs.com.au (Harry McNally) Date: Mon, 11 Oct 2010 08:37:30 +0800 Subject: [RadioTelescope] beaten to the punch? In-Reply-To: References: Message-ID: <4CB25C4A.5030409@decisions-and-designs.com.au> Optical tho' ? David Adam wrote: > http://www.icrar.org/news/news_items/new_telescope_puts_focus_on_high_school_discoveries > > [DAA] From harrymc at decisions-and-designs.com.au Mon Oct 11 08:40:25 2010 From: harrymc at decisions-and-designs.com.au (Harry McNally) Date: Mon, 11 Oct 2010 08:40:25 +0800 Subject: [RadioTelescope] Stepping rates Message-ID: <4CB25CF9.5090709@decisions-and-designs.com.au> Hello Telescopists Has anyone derived the range of stepping rates required in azimuth and elevation ? Harry From andrew at physics.uwa.edu.au Mon Oct 11 12:45:58 2010 From: andrew at physics.uwa.edu.au (Andrew Williams) Date: Mon, 11 Oct 2010 12:45:58 +0800 Subject: [RadioTelescope] Stepping rates In-Reply-To: <4CB25CF9.5090709@decisions-and-designs.com.au> References: <4CB25CF9.5090709@decisions-and-designs.com.au> Message-ID: <4CB29686.2010500@physics.uwa.edu.au> On 11/10/2010 8:40 AM, Harry McNally wrote: > Hello Telescopists > > Has anyone derived the range of stepping rates required in azimuth and elevation ? The formal treatment gets really messy, because there's a singularity in the az/el coordinate system at the zenith - you need to slew infinitely fast in azimuth to track a source that goes directly overhead. In practice, the dish is small so the beamsize is huge - a few degrees across - and the chances of a target tracking precisely overhead is small. Slew rates only need to be fast enough to be convenient for users, and since (with a small dish) you'll be staying on any one target to integrate over quite long times (tens of minutes?), it doesn't matter if it takes a minute or two to go between targets. Obviously the faster it slews the better, but I wouldn't plan on trying for worst-case point-to-point slew times any better than tens of seconds. As an example, the Parkes 64m dish takes about quarter of an hour to do a complete rotation in azimuth. The worst-case slew time is a complete (360 degree) rotation in azimuth. You might think it would only be 180 degrees, but you need to allow for cable-wrap constraints - you can't keep spinning the dish round and round like in 'The Exorcist'... (BTW, I'd plan on cable-wrap limits in hardware, not software, especially if you're going to allow a bit more than 360 degrees...) Andrew From harrymc at decisions-and-designs.com.au Mon Oct 11 13:34:32 2010 From: harrymc at decisions-and-designs.com.au (Harry McNally) Date: Mon, 11 Oct 2010 13:34:32 +0800 Subject: [RadioTelescope] Stepping rates In-Reply-To: <4CB29686.2010500@physics.uwa.edu.au> References: <4CB25CF9.5090709@decisions-and-designs.com.au> <4CB29686.2010500@physics.uwa.edu.au> Message-ID: <4CB2A1E8.9090505@decisions-and-designs.com.au> Hi Andrew Andrew Williams wrote: > On 11/10/2010 8:40 AM, Harry McNally wrote: >> Hello Telescopists >> >> Has anyone derived the range of stepping rates required in azimuth and >> elevation ? > > The formal treatment gets really messy, because there's a singularity in > the az/el coordinate system at the zenith - you need to slew infinitely > fast in azimuth to track a source that goes directly overhead. Yes. Remembered that from your previous email. I'm pondering more what the maximum step rate is that the motors can deliver (torque-wise) although I presume that's pretty high when the dish is accelerated up to that limit. > In practice, the dish is small so the beamsize is huge - a few degrees > across - and the chances of a target tracking precisely overhead is > small. Slew rates only need to be fast enough to be convenient for > users, and since (with a small dish) you'll be staying on any one target > to integrate over quite long times (tens of minutes?), it doesn't matter > if it takes a minute or two to go between targets. Ok. The problem is I don't know the gearbox reductions for az and el to motor steps yet so that will have to be figured out if there isn't a drawing with the data. > Obviously the faster it slews the better, but I wouldn't plan on trying > for worst-case point-to-point slew times any better than tens of > seconds. As an example, the Parkes 64m dish takes about quarter of an > hour to do a complete rotation in azimuth. Impressive :) > The worst-case slew time is a complete (360 degree) rotation in azimuth. > You might think it would only be 180 degrees, but you need to allow for > cable-wrap constraints - you can't keep spinning the dish round and > round like in 'The Exorcist'... > > (BTW, I'd plan on cable-wrap limits in hardware, not software, > especially if you're going to allow a bit more than 360 degrees...) Ok. There are no limit switches that I can recall on the mount. Cheers Harry > Andrew > > From harrymc at decisions-and-designs.com.au Mon Oct 11 14:50:41 2010 From: harrymc at decisions-and-designs.com.au (Harry McNally) Date: Mon, 11 Oct 2010 14:50:41 +0800 Subject: [RadioTelescope] Paper documentation Message-ID: <4CB2B3C1.6080404@decisions-and-designs.com.au> Hello list I was about to go get the serial numbers of the GDM (stepper driver) boards to request a copy of the technical manual. Has someone already done this ? If not (and also) is there paper documentation and circuits for the project and how can I get access to them ? All the best Harry From andrew at physics.uwa.edu.au Mon Oct 11 17:36:10 2010 From: andrew at physics.uwa.edu.au (Andrew Williams) Date: Mon, 11 Oct 2010 17:36:10 +0800 Subject: [RadioTelescope] Stepping rates In-Reply-To: <4CB2A1E8.9090505@decisions-and-designs.com.au> References: <4CB25CF9.5090709@decisions-and-designs.com.au> <4CB29686.2010500@physics.uwa.edu.au> <4CB2A1E8.9090505@decisions-and-designs.com.au> Message-ID: <4CB2DA8A.1080105@physics.uwa.edu.au> On 11/10/2010 1:34 PM, Harry McNally wrote: > Yes. Remembered that from your previous email. I'm pondering more what the > maximum step rate is that the motors can deliver (torque-wise) although I > presume that's pretty high when the dish is accelerated up to that limit. You'll need to measure the maximum reasonable accelleration rates and slew speeds after the system is built, it'll depend on drivetrain friction, moment of inertia of the dish (and all rotating components in the drivetrain), etc. Too hard to bother trying to calculate... > Impressive :) What's really impressive is the way they allowed the Parkes telescope, with an azimuth/elevation drive to track objects in right-ascension and declination (curved paths across the sky) in the 50's, before computers... In the exact centre of the az/el drive system, they had a small chamber with a dummy 'telescope' on an equatorial mount - one axis pointed to align with the Earth's polar axis (RA, or 'longitude' on the sky), the other at right angles (Dec, or 'latitude' on the sky). To track an object with an equatorial mount, you keep the Dec axis fixed, and rotate the RA axis at one revolution per day, to counteract the Earth's rotation. That central equatorial 'dummy telescope' was first slewed to the desired target coordinates, and set tracking the object. Then the az/el drive of the dish was manually slewed to line up with the same direction, to within a few degrees. Once the position was close enough, they activated a servo link with a light beam and a set of photocells between the az/el drive on the dish and the tracking motion of the central equatorial mounted dummy telescope. >> (BTW, I'd plan on cable-wrap limits in hardware, not software, >> especially if you're going to allow a bit more than 360 degrees...) > > Ok. There are no limit switches that I can recall on the mount. If there's an encoder, you could simply enforce not being able to pass through, say, 0 degrees azimuth, in either direction. That would be irritating, since if you were tracking an object, you'd have to break away and slew the long way round - there's no single azimuth value that you aren't going to want to 'track through' quite often (and 0 degrees, due north, is a really bad choice). A better way would be to allow, say, 540 (or more) degrees of travel. If you slew to a new object, you calculate the direction to 'unwind' to the most central cable-wrap azimuth, but if tracking, you could continue in one direction for much longer. The problem is that if your encoder only gives you azimuth angle, you need to keep track of cable-wrap boundaries by dead-reckoning, and guarantee storing that state between uses. Without cable-wrap limit switches, I'd make sure you design some quick-release connectors in the middle of the cables (or at one end), so that if the software fails to keep track of state, it's an easy fix... Andrew From harrymc at decisions-and-designs.com.au Mon Oct 11 18:20:03 2010 From: harrymc at decisions-and-designs.com.au (Harry McNally) Date: Mon, 11 Oct 2010 18:20:03 +0800 Subject: [RadioTelescope] Stepping rates In-Reply-To: <4CB2DA8A.1080105@physics.uwa.edu.au> References: <4CB25CF9.5090709@decisions-and-designs.com.au> <4CB29686.2010500@physics.uwa.edu.au> <4CB2A1E8.9090505@decisions-and-designs.com.au> <4CB2DA8A.1080105@physics.uwa.edu.au> Message-ID: <4CB2E4D3.4070709@decisions-and-designs.com.au> Hi again Andrew Williams wrote: > On 11/10/2010 1:34 PM, Harry McNally wrote: > A better way would be to allow, say, 540 (or more) degrees of travel. If > you slew to a new object, you calculate the direction to 'unwind' to the > most central cable-wrap azimuth, but if tracking, you could continue in > one direction for much longer. Why don't we digitise in both directions and use a wireless link to the dish electronics ? All we need then is a slip ring for the mains supply on the azimuth and we can ignore azimuth limits. See: http://www.eslipring.com/en/index.aspx I'm presently pondering an arduino I have here as a lash up for stepper clocks and directions with some serial strings to define ramp up and down and total steps for each axis, a preload of the next move and a "go" command that allows the two movements to happen in sync. It won't need to worry about axis limits initially but could be used to work out the motion limits of the dish. All the best Harry From andrew at physics.uwa.edu.au Mon Oct 11 18:46:30 2010 From: andrew at physics.uwa.edu.au (Andrew Williams) Date: Mon, 11 Oct 2010 18:46:30 +0800 Subject: [RadioTelescope] Stepping rates In-Reply-To: <4CB2E4D3.4070709@decisions-and-designs.com.au> References: <4CB25CF9.5090709@decisions-and-designs.com.au> <4CB29686.2010500@physics.uwa.edu.au> <4CB2A1E8.9090505@decisions-and-designs.com.au> <4CB2DA8A.1080105@physics.uwa.edu.au> <4CB2E4D3.4070709@decisions-and-designs.com.au> Message-ID: <4CB2EB06.5000802@physics.uwa.edu.au> On 11/10/2010 6:20 PM, Harry McNally wrote: > > Why don't we digitise in both directions and use a wireless link to the dish > electronics ? All we need then is a slip ring for the mains supply on the > azimuth and we can ignore azimuth limits. That's fine for the drive system, but there's also the actual receiver to worry about - at a minimum, that will be a single 50 ohm coax, more likely a coax pair, maybe more... Andrew From harrymc at decisions-and-designs.com.au Mon Oct 11 21:09:06 2010 From: harrymc at decisions-and-designs.com.au (Harry McNally) Date: Mon, 11 Oct 2010 21:09:06 +0800 Subject: [RadioTelescope] Stepping rates In-Reply-To: <4CB2EB06.5000802@physics.uwa.edu.au> References: <4CB25CF9.5090709@decisions-and-designs.com.au> <4CB29686.2010500@physics.uwa.edu.au> <4CB2A1E8.9090505@decisions-and-designs.com.au> <4CB2DA8A.1080105@physics.uwa.edu.au> <4CB2E4D3.4070709@decisions-and-designs.com.au> <4CB2EB06.5000802@physics.uwa.edu.au> Message-ID: <4CB30C72.2000208@decisions-and-designs.com.au> Hi Andrew Andrew Williams wrote: > On 11/10/2010 6:20 PM, Harry McNally wrote: >> >> Why don't we digitise in both directions and use a wireless link to >> the dish >> electronics ? All we need then is a slip ring for the mains supply on the >> azimuth and we can ignore azimuth limits. > > That's fine for the drive system, but there's also the actual receiver > to worry about - at a minimum, that will be a single 50 ohm coax, more > likely a coax pair, maybe more... Ok. I was either being ambitious (put all the radio electronics out on the dish) or you -could- buy a slip ring that includes coax connections. They are available with many different options. Have another look at that link again, it's mainly signal rather than power connections including fibre. It even lists radio telescopes here: http://en.wikipedia.org/wiki/Slip_ring Harry From andrew at physics.uwa.edu.au Mon Oct 11 21:51:56 2010 From: andrew at physics.uwa.edu.au (Andrew Williams) Date: Mon, 11 Oct 2010 21:51:56 +0800 Subject: [RadioTelescope] Stepping rates In-Reply-To: <4CB30C72.2000208@decisions-and-designs.com.au> References: <4CB25CF9.5090709@decisions-and-designs.com.au> <4CB29686.2010500@physics.uwa.edu.au> <4CB2A1E8.9090505@decisions-and-designs.com.au> <4CB2DA8A.1080105@physics.uwa.edu.au> <4CB2E4D3.4070709@decisions-and-designs.com.au> <4CB2EB06.5000802@physics.uwa.edu.au> <4CB30C72.2000208@decisions-and-designs.com.au> Message-ID: <4CB3167C.80309@physics.uwa.edu.au> On 11/10/2010 9:09 PM, Harry McNally wrote: > Ok. I was either being ambitious (put all the radio electronics out on the > dish) or you -could- buy a slip ring that includes coax connections. They are > available with many different options. > > Have another look at that link again, it's mainly signal rather than power > connections including fibre. > > It even lists radio telescopes here: > http://en.wikipedia.org/wiki/Slip_ring I suspect all the slip rings are expensive, and that the high-frequency and optical fibre slip rings are staggeringly expensive... Also, it probably won't be UCC that builds the receiver electronics - it's likely to be a commercial or custom made feed horn and low noise amplifier unit that someone at UWA or Curtin has lying around, probably needing dual 50 ohm coax with DC power for the LNA's via the coax (and those 500MHz slip rings might not work down at DC). If there any RF hardware hackers around UCC, they could probably adapt a Foxtel satellite horn and LNA's - not sure what frequency or bandwidth they would use though. Then you'd need all the gear to digitise the result - computer controlled signal generator, ADC, etc. The individual components are likely to be lying around physics, or you (or Physics) could just buy a complete USRP kit: http://www.ettus.com/. The MWA folks were using a USRP2 and a wideband antenna to do RFI monitoring at Boolardy on the last site visit - they picked up a signal at 98.9 Mhz, fired up Gnu Radio on the server collecting the data, and listened to JJJ from Geraldton... Andrew From harrymc at decisions-and-designs.com.au Tue Oct 12 10:15:32 2010 From: harrymc at decisions-and-designs.com.au (Harry McNally) Date: Tue, 12 Oct 2010 10:15:32 +0800 Subject: [RadioTelescope] Stepping rates In-Reply-To: <4CB3167C.80309@physics.uwa.edu.au> References: <4CB25CF9.5090709@decisions-and-designs.com.au> <4CB29686.2010500@physics.uwa.edu.au> <4CB2A1E8.9090505@decisions-and-designs.com.au> <4CB2DA8A.1080105@physics.uwa.edu.au> <4CB2E4D3.4070709@decisions-and-designs.com.au> <4CB2EB06.5000802@physics.uwa.edu.au> <4CB30C72.2000208@decisions-and-designs.com.au> <4CB3167C.80309@physics.uwa.edu.au> Message-ID: <4CB3C4C4.8010408@decisions-and-designs.com.au> Hi Andrew Andrew Williams wrote: > I suspect all the slip rings are expensive, and that the high-frequency > and optical fibre slip rings are staggeringly expensive... Yes. Cost is an issue, true. Getting ahead of myself here. Tho' who said UCC projects needed sober practicality ;-) > The MWA folks were using a USRP2 and a wideband antenna to do RFI > monitoring at Boolardy on the last site visit - they picked up a signal > at 98.9 Mhz, fired up Gnu Radio on the server collecting the data, and > listened to JJJ from Geraldton... :-) Thanks Harry From reapsta at gmail.com Thu Oct 14 11:45:43 2010 From: reapsta at gmail.com (Craig Williams) Date: Thu, 14 Oct 2010 11:45:43 +0800 Subject: [RadioTelescope] beaten to the punch? In-Reply-To: <4CB25C4A.5030409@decisions-and-designs.com.au> References: <4CB25C4A.5030409@decisions-and-designs.com.au> Message-ID: Trying to get access to this for 'research' purposes (i bet we can make it better) On 11 October 2010 08:37, Harry McNally < harrymc at decisions-and-designs.com.au> wrote: > Optical tho' ? > > David Adam wrote: > > > http://www.icrar.org/news/news_items/new_telescope_puts_focus_on_high_school_discoveries > > > > [DAA] > _______________________________________________ > RadioTelescope mailing list > RadioTelescope at ucc.gu.uwa.edu.au > http://lists.ucc.gu.uwa.edu.au/mailman/listinfo/radiotelescope > -------------- next part -------------- An HTML attachment was scrubbed... URL: http://lists.ucc.gu.uwa.edu.au/pipermail/radiotelescope/attachments/20101014/f42f88ea/attachment.htm