Re: [time-nuts] TrueTime AL-AK GPS receiver help
Hi If you want to dig into something like this to learn and to maybe fiddle with a downconverter design - sure, that’s a great thing to do. It’s a hobby and (hopefully) you are set up to handle the task. You probably are already a member of a list (or three) where you have access to info on your project. Since we have zero info about the original requester, I am indeed guessing here. That can often be a bad thing to do. My *guess* is that this is somebody who simply wants a working device. If so, there are a lot of bumps in the road that they need to understand. If the answer is “I want a simple NTP server that is setup and forget”, this is probably not the way to go. Bob On May 1, 2015, at 9:55 PM, paul swed paulsw...@gmail.com wrote: Bob brings up all the additional details that are the reality of dealing with teh older gear. Especially the date offsets because of the 1024 week cycle. That is a real pain. But the reason to spend time on something like this is to understand something and to learn. I picked up the austron 2000 gps because it was a useful rack mount box. Then realized some of its unique qualities. That was the driver for reviving it. I was lucky that I was able to obtain some operational data and then later schematics. BUT it was still a heck of a reverse engineering and adapting process. I am pretty sure I shared that on time-nuts and will guess that must be 5 years ago now. Regards Paul WB8TSL On Thu, Apr 30, 2015 at 5:58 PM, Bob Camp kb...@n1k.org wrote: Hi I guess the first question would be: Are we sure it’s an AL-AK and not an XL-AK? Past that it becomes a fairly involved process of, is it worth real money to get this up and running? If we are talking about a $20 eBay find that is worth another $5 to have somebody else get it running, the conversation is a real short one. If the AL-AK has some inherent value (it’s a working GPS disciplined Cs maybe) then putting a few hundred dollars into checking it out and getting it running might make sense. If it’s like most of the parts from that era, the delta between getting it checked and getting it running is pretty small. Once you *do* have it running, what do you have? 1) Leap second problems 2) GPS year rollover problems 3) Tracking issues 4) A noisy receiver with very few correlators 5) Software support issues This is an unusual box that is at least 20 years old. It *will* have at least some of the listed issues and may have all of them. Fixing them will be impossible. Why bring up all of the negatives? I for one have been sucked into this kind of thing a *lot* of times in the past. Just a few more this or that and it’ll be running fine. Much better to figure out the likely cost and outcome first. That’s *very* hard to do, and even harder to follow through on. If you can’t do the work yourself, the cost isn’t just lost time. This can cost real cash. Bob On Apr 30, 2015, at 12:50 PM, Tom Van Baak t...@leapsecond.com wrote: I received this email. Anyone have a good answer? Thanks, /tvb -- Someone on ebay advised me to contact your website in hopes that someone in your organization can help me with my TrueTime model AL-AK GPS Receiver. I need to send it to someone so that they can check it to see if it works and can track Satellites. This receiver has the onboard up/down convertor board that changes the receiver input frequency which is set at 4.092 MHz. I don't have the needed down converter at the antenna. I bought this receiver on ebay from someone who told me that he doesn't have the down converter as well and can't figure out how to get it to work at 1575.42 MHz. He also didn't know if this receiver can be setup for a 1575.42 MHz by removing the onboard converter and changing some DIP switches. If one of your members can at least check out the receiver at 4.092 MHz for satellite tracking That would be a big help ... -- ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] TrueTime AL-AK GPS receiver help
Hi Remember - a number of these boxes go *way* back in time GPS wise. Often the basic guts were a mix and match affair and this or that sub-system was frozen for a decade or more. At this late date, figuring out why they did that, or why they had multiple sub-systems is going to be tough. I suspect that it goes something like - this one works with 1500’ of RG-58, that one works with 300’ of RG-58. In answer to your basic question - I’d bet it has the IF to a GPS receiver and the tuned front end is up at the antenna. I have never seen one of these that was an either or as installed. If you wanted a downconverter, that’s what they built into the box. If you wanted a full receiver, that went in instead. They flipped a few dip switches on the main board to tell the firmware what it had and moved on. Bob On May 2, 2015, at 12:10 AM, Al Wolfe alw.k...@gmail.com wrote: Does this AL-AK have a real GPS receiver in it? Does the unit have a board with a crystal of 16.368MHz. that is multiplied by 96 up to 1571.328, the mixing frequency to get to the GPS freq of 1575.42? Since the down convert-up convert is offered as an option perhaps TrueTime used an actual GPS receiver in all their units. It stands to reason (at least to me) using a stock off-the-shelf GPS receiver in all their boxes would be simpler than having to do a custom kluge to work at 4 mhz. If this user can find out if his box has an actual GPS receiver then the converter section could probably be bypassed. FWIW, the TrueTime XL-AK used an external up converter and down converter, model 142-6150. Says it's good for up to 1500 feet of RG58. Its manual is on line. It uses the above mixing scheme. Al, retired, mostly AKA k9si Someone on ebay advised me to contact your website in hopes that someone in your organization can help me with my TrueTime model AL-AK GPS Receiver. I need to send it to someone so that they can check it to see if it works and can track Satellites. This receiver has the onboard up/down convertor board that changes the receiver input frequency which is set at 4.092 MHz. I don't have the needed down converter at the antenna. I bought this receiver on ebay from someone who told me that he doesn't have the down converter as well and can't figure out how to get it to work at 1575.42 MHz. He also didn't know if this receiver can be setup for a 1575.42 MHz by removing the onboard converter and changing some DIP switches. If one of your members can at least check out the receiver at 4.092 MHz for satellite tracking That would be a big help ... snip ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Important parameters for a GPS/GNSS antenna
Hi Obviously this becomes a “that depends” sort of question. For timing, you probably can do a fine job with an antenna that nukes everything below 20 degrees to the horizon. That *assumes* that you have a good enough view that it does not pull to many sat’s out of your population *and* that you already know your location. Phase / delay stability over temperature would be an interesting thing to look at. Probably not a big deal on a simple antenna. It might be an issue as the antenna interacts with the preamp and filter. Bob On May 2, 2015, at 12:36 PM, Magnus Danielson mag...@rubidium.dyndns.org wrote: Attila, On 04/29/2015 10:43 PM, Attila Kinali wrote: Moin, I recently discovered openEMS[1], which is, very simply put, a fancy antenna simulator. I played a little with it and thought about trying to optimize an GPS patch antenna design for timing use. Will take it for a test-drive to see how it align up to NEC2 and variants. But I had to discover that I actually do not know what to optimze for. There are many paramters I can think of (RHCP/LHCP, symmetry of gain, feedpoint impedance vs frequency, stability of phase centre,) which all seem to be to some extend important, but which ones do actually matter for the timing reference performance? My google skills failed to locate any relevant documents on this topic. Could someone be so kind and give me some pointers, what to search for, documents or the like? The thing that we care about is: 1) LHCP surpression 2) Directivity/ surpression of signals below say 5 degrees above horizon 3) Phase stability with regard to azimuth/elevation 4) Relatively flat gain above 5 degrees Do read up on the Novatel pinwheels, as they illustrate the various concerns and how they do that in a new fashion. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Important parameters for a GPS/GNSS antenna
A tri-band antenna design is... uh.. difficult. At the moment I am just playing with some software. Yes, I might end up with something that resembles an antenna design. But with my level of knowledge getting a good single band antenna would be already quite some feat. Designing a multi-band antenna is way out of my league. Attila Kinali Hi Attila, One other consideration is that for high-end positioning and timing use, an accurate characterization of a given antenna is more important than trying to achieve a perfect antenna. When you post-process raw GPS data you get to include antenna phase center / gain / az/el corrections for free. This means the goal is not so much a perfect antenna design, but an antenna whose imperfections are well-known. Here are a dozen random GPS antenna calibration links to keep you busy for today: National Geodetic Survey Absolute Antenna Calibrations http://www.gps.gov/cgsic/meetings/2010/bilich.pdf Leica GNSS Reference Antennas - White Paper http://www.leica-geosystems.com/downloads123/zz/nrs/general/white-tech-paper/Leica_Reference_Antennas_Whitepaper_TPA_en.pdf A Novel GPS Survey Antenna http://www.meridware.com.tw/Documents/Papers/gps600antenna.pdf Tests of phase center variations of various GPS antennas, and some results ftp://geodesy.noaa.gov/pub/abilich/oldPC/Documents/antcal/calibPapers/Schmitz2002.pdf GPS ANTENNA CALIBRATION AT THE NATIONAL GEODETIC SURVEY https://www.fig.net/pub/fig2008/ppt/ts05g/ts05g_02_weston_mader_ppt_2857.pdf A New Approach for Field Calibration of Absolute Antenna Phase Center Variations http://www.geopp.com/pdf/ion96.pdf ANTENNA PHASE CENTER VARIATIONS CORRECTIONS IN PROCESSING OF GPS OBSERVATIONS WITH USE OF COMMERCIAL SOFTWARE http://www.uwm.edu.pl/wnt/technicalsc/tech_13/B12.PDF Phase center variations problem in GPS/GLONASS observations processing http://leidykla.vgtu.lt/conferences/ENVIRO_2014/Articles/5/202_Dawidowicz.pdf Calibration of antenna-radome and monument-multipath effect of GEONET—Part 1: Measurement of phase characteristics http://svr4.terrapub.co.jp/journals/EPS/pdf/2001/5301/53010013.pdf Absolute phase center corrections of satellite and receiver antennas http://www.dgfi.tum.de/media/jahresbericht/publications/4558dbb6f6f8bb2e16d03b85bde76e2c.pdf Phase Center Calibration and Multipath Test Results of a Digital Beam-Steered Antenna Array http://navsys.com/Papers/0309002.pdf /tvb ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
Re: [time-nuts] Important parameters for a GPS/GNSS antenna
Attila, On 04/29/2015 10:43 PM, Attila Kinali wrote: Moin, I recently discovered openEMS[1], which is, very simply put, a fancy antenna simulator. I played a little with it and thought about trying to optimize an GPS patch antenna design for timing use. Will take it for a test-drive to see how it align up to NEC2 and variants. But I had to discover that I actually do not know what to optimze for. There are many paramters I can think of (RHCP/LHCP, symmetry of gain, feedpoint impedance vs frequency, stability of phase centre,) which all seem to be to some extend important, but which ones do actually matter for the timing reference performance? My google skills failed to locate any relevant documents on this topic. Could someone be so kind and give me some pointers, what to search for, documents or the like? The thing that we care about is: 1) LHCP surpression 2) Directivity/ surpression of signals below say 5 degrees above horizon 3) Phase stability with regard to azimuth/elevation 4) Relatively flat gain above 5 degrees Do read up on the Novatel pinwheels, as they illustrate the various concerns and how they do that in a new fashion. Cheers, Magnus ___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
[time-nuts] DDS, OCXO and ADEV
Hello, I would like to create some charts for ADEV for following setup: HP5386A counter connected to External REF. (OCXO). The input of counter connected to my DDS VFO. The frequency on VFO is 2853000 Hz. Here is what I got from counter via GPIB: S +3.505082408E-7 S +3.505082408E-7 S +3.505082408E-7 S +3.505082408E-7 S +3.505082408E-7 S +3.505082408E-7 S +3.505082408E-7 S +3.505082409E-7 S +3.505082408E-7 S +3.505082409E-7 S +3.505082408E-7 S +3.505082408E-7 S +3.505082408E-7 I converted it to following form: 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240800 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240900 0.00350508240900 Then I tried to use ADEV by tvb (long life to Tom!). See attached file 1b.bmp And I tried to create the charts for the collected data. See attached file 1a.bmp. But it seems I am doing something wrong. Any advises will be greatly appreciated. Thanks ! -- WBW, V.P.___ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
