Any info on TruePosition 101333 also know as LMU300? - Page 1
Forum section: electronics / general

author: WPXS472
author_rank: Regular Contributor
timestamp: April 24, 2020, 01:40:43 pm
content: These are available on eBay currently for $29 plus shipping. They are the source for the fairly common TruePosition GPSDO boards. I bought one, and it arrived yesterday. It is a 1U rack mount unit that appears unused. It has the GPSDO inside, but it is different to the one I already had. Thing is, there is a whole bunch of other stuff as well. I assume it produces timing signals, but I don't really know. A Google search only turned up the eBay ads and a couple of telecom sellers offering them for sale. Does anyone have, or know where I can find some detailed information on these? I searched the forum, and there were posts that mentioned TruePosition, but nothing specific on this unit.

author: Theboel
author_rank: Frequent Contributor
timestamp: April 24, 2020, 02:56:10 pm
content: Quote from: WPXS472 on April 24, 2020, 01:40:43 pmI spend a lot of time do searching for any info about this equipment. the cost is negligible compare to quality. the best I could if i not mistaken is block diagram of the main system of 911 emergency system from trueposition. I will try to find it in my old archive file.

author: WPXS472
author_rank: Regular Contributor
timestamp: April 24, 2020, 04:43:58 pm
content: They have a really weird connector. It took a while to identify it. Managed to find a jumper that adapts to SMA on eBay. I hooked it up and although it says it takes 6 amps at 24 volts, it actually took less than 2. After a couple of minutes, the GPS and alarm lights showed green with the state blinking yellow. I managed to get an SMA male to make a temporary contact with the 10 MHz output, and the frequency wasn't close when compared to my RFTGu. It has USB and Ethernet connectors. I just wonder if it has to have the $PROCEED command entered before it will actually work. It is full of really neat but unknown stuff, and I would rather leave all that in, though I don't have an idea what it does. If all else fails, I will take out the GPSDO.

author: Nuno_pt
author_rank: Frequent Contributor
timestamp: April 24, 2020, 04:54:17 pm
content: See if this helps <https://time-nuts.febo.narkive.com/XeJowavM/trueposition-gps-receiver>

author: WPXS472
author_rank: Regular Contributor
timestamp: April 25, 2020, 03:19:31 am
content: Thanks, that helped.

author: bingo600
author_rank: Super Contributor
timestamp: April 25, 2020, 01:05:39 pm
content: A post on "time-nuts" said it needed a signal on the T1/E1 in order to work.I suppose the gpsdo is the only "generally" usable part in that chassis.Whish i could get it to EU for something "close to" $29 ... But no chance.Shipping is ~50$ , and then 25% VAT on $80 on top./Bingo

author: Theboel
author_rank: Frequent Contributor
timestamp: April 25, 2020, 01:19:03 pm
content: I curious what the parts in the small metallic block ?

author: WPXS472
author_rank: Regular Contributor
timestamp: April 25, 2020, 05:01:53 pm
content: I am not sure exactly what you mean by small metallic block. There are several shielded housings on the top, large board. I took the covers off a few and there is quite a bit of small electronics underneath. There are several Minicircuits devices as well, though it doesn't appear the top can be removed. One of the inscriptions is BPF144, which makes me think they could be 144 MHz bandpass filters. Or would Minicircuits be giving away too much? Most of the Minicircuits stuff I have seen in actual manufactured electronics was house numbered. Only occasionally do I see a number than can be looked up on their website. Since there is no readily available information on how this operates as a unit, it looks like I will be forced to just remove the GPSDO and see if I can get it to operate separately. The Time Nuts information referenced above will provide a good starting point. One thing I noticed was that it has a fairly large, and pretty complex DC/DC converter. I was expecting several voltages out of it, but when I probed around on it, the only voltage I saw leaving as 12 Volts. Funny. Every RF connector except the GPS antenna connector is a QMA connector. This is the first time I have seen these, and I hope it is the last. I will begin parting it out soon. If I discover anything of interest, I will post it here. Thanks to those who have helped.

author: Theboel
author_rank: Frequent Contributor
timestamp: April 25, 2020, 05:24:31 pm
content: I just found this interesting linkhttps://www.circuitvalley.com/2018/07/diy-isolated-10mhz-distribution-amp-gpsdo-rubidium-tcxo-reference.html

author: bingo600
author_rank: Super Contributor
timestamp: April 25, 2020, 07:13:35 pm
content: Seller is a nice personHe can be convinced to just ship the GPSDO Board w. cableshttps://www.ebay.com/itm/164174427150Makes shipping a lot better for EU/Bingo

author: ZigmundRat
author_rank: Regular Contributor
timestamp: April 26, 2020, 03:18:45 am
content: I don't think it's been mentioned but these units were part of a 3G E911 TDOA triangulation cellular locator system. (Caller dials 911, system tries to find where they are - these days handsets all have gps.)I spent a fair amount of time poking around these units and came to the conclusion that for me at least, the most valuable 'part' was the GPSDO. The balance of the rather nice circuitry and components didn't seem generic enough to be useful to me. Of course, YMMV. My finding was that without a T1 timing source it would just boot loop. You could interrupt that loop by going into VxWorks and poking at it, but it doesn't get you very far. It's just not going to do much without the rest of the system.If it's of any use, I put the installation manual up on my Dropbox <https://www.dropbox.com/s/hs6bqczpmf2ww59/documents.mx_lmu3g-install-na-2528.pdf?dl=0> That's manual is all the doc I could dig up. There are a couple other manuals referenced but I couldn't locate them online.Cheers!