Can you help identifying this GPSDO module? - Page 1
Forum section: electronics / projects

author: tic226
author_rank: Newbie
timestamp: November 13, 2021, 11:42:32 am
content: Hi,yesterday i came across an interesting ebay listing of what seems like a commercial GPSDO module. (3 pictues attached)The seller doesn't have any information about it only that it was pulled fom a Harris DBT transmitter and that it has anOCXO in it. Searching for the part number and various combinations of 'Harris DBT transmitter' only lead me to an italiansurplus seller (0) and judging from the pictures it looks like the transmitter in question is a Harris DBT-050U or similar.Looking at the PCB i can only identify the OCXO module (lower right corner), a GPS receiver, the PLL around the Philips PLCC ICand the Xilinx FPGA which might run some software (stored in the labelled E(E)PROM) to pull it all together.Other than that, the top layer seems to be a large ground plane, i assume there are some more components on theback which might lead to identifying a UART interface or something else to talk to the module but i don't have photos of that.Initially i was only looking for an OCXO and build the tuning circuit myself but if this module is able to work autonomouslywithout being attached to a controller module i could simply use the 1Hz and 10MHz outputs and be done with it.Have you seen such a module and might even know if it would be sensible to buy it?(0)http://www.telecomponents.com/catalog/agile-digital-tv-transmitter-dvbt-screen-dvb-t-uhf-p-661.html

author: max-bit
author_rank: Frequent Contributor
timestamp: November 13, 2021, 12:43:09 pm
content: But I do not see any quartz resonator here, the more compensated (PCB on the right?) But also something not entirely

author: tic226
author_rank: Newbie
timestamp: November 13, 2021, 12:55:01 pm
content: Quote from: max-bit on November 13, 2021, 12:43:09 pmDo you mean the OCXO? It's on the underside of the PCB module in the lower right corner, marked '789497-001 02'.If you look closely you can spot 5 THT pins in a layout often used for OCXOs.

author: max-bit
author_rank: Frequent Contributor
timestamp: November 13, 2021, 01:08:26 pm
content: OKYou would have to try to run it, it is probably powered by 2-3 "voltages". If it starts without external control, you have GPSDO, if not then ...

author: tic226
author_rank: Newbie
timestamp: November 13, 2021, 01:25:01 pm
content: Quote from: max-bit on November 13, 2021, 01:08:26 pmI'm inclined to buy and do just that. If it doesn't run or i absolutely cannot identify where and how to power it i still could just pull outthe OCXO module. The price for the whole thing is only slighly higher than i what i would have to pay for a 'naked' OCXO.But maybe someone on here has worked with these devices and can give me a few pointers on how to get this thing running ORtell me it's a bad idea before i pull the trigger on the sale.

author: AndrewBCN
author_rank: Frequent Contributor
timestamp: November 13, 2021, 01:44:37 pm
content: This is a waste of time and money. An ancient piece of hardware like that one, without documentation, is just a paperweight.You can find modern GPSDOs that will work right out of the box on the internet for < $100. Why would you buy a piece of junk instead?

author: tic226
author_rank: Newbie
timestamp: November 13, 2021, 02:26:09 pm
content: Quote from: AndrewBCN on November 13, 2021, 01:44:37 pmSo far i could only find GPSDOs for significantly more than EUR100, except for a few chinese models (~EUR80) which don't come withdocumentation either. This Harris module is EUR59 and would only involve domestic shipping. But what you're saying makes a lot of sense,it would be too risky to buy this thing.When i saw the listing yesterday i initially thought about another thread (0) where people were discussing a Symmetricom module. Thoseare available for only EUR30 on ebay but sadly they don't come with an OCXO.(0)https://www.eevblog.com/forum/projects/a-look-at-my-symmetricom-gpsdo-(ocxo-furuno-receiver)/msg807174/#msg807174

author: AndrewBCN
author_rank: Frequent Contributor
timestamp: November 13, 2021, 04:13:48 pm
content: I would suggest you take a look at the three DIY GPSDO open-source projects right here in the Projects EEVblog forum; all three can be built for < 59€ and a few hours of your spare time.- Lars' GPSDO. (uses an AVR MCU)- MIS42N GPSDO. (uses a PIC MCU)- STM32 GPSDO. (uses an STM32 MCU)

author: tic226
author_rank: Newbie
timestamp: November 13, 2021, 04:42:12 pm
content: Quote from: AndrewBCN on November 13, 2021, 04:13:48 pmThank you for the suggestions, incidentally i am about to build Lars' GPSDO and was on the hunt for a suitable oscillator on ebay. That's wheni came across the above mentioned listing of the Harris module (which has an OCXO). Best option i found so far is an OCXO in good conditionfor ~40 so i guess i'll go with that.

author: AndrewBCN
author_rank: Frequent Contributor
timestamp: November 13, 2021, 08:59:04 pm
content: Check the STM32 GPSDO thread. There are at least three different 10MHz 5V square wave OCXOs that you can purchase for < 10€ per piece, which I listed there.

author: tic226
author_rank: Newbie
timestamp: November 13, 2021, 10:03:05 pm
content: Quote from: AndrewBCN on November 13, 2021, 08:59:04 pmOh that looks very interesting! A quick search on Aliexpress shows that the oscillator would cost only EUR7.91 including postage. Interestingly, the ones i found on ebayare the same type but mounted on a PCB with a badly designed power supply for a much higher price. Thank you for the advice, time to read through another long thread.

author: cdev
author_rank: Super Contributor
timestamp: November 14, 2021, 12:29:20 am
content: See if you can find a TruePosition GPSDO telco surplus. Its a really good GPSDO, is well documented here, and I have seen them for as little as $35.They may be one of the better GPSDOs available. I think thats a good possibility. I agree that an older, unknown GPSDO is likely not a good buy, without the needed information to utilize it. Good luck!Quote from: tic226 on November 13, 2021, 02:26:09 pm