[time-nuts] Has anybody checked this? GPSDO in kit

Giuseppe Marullo giuseppe at marullo.it
Sun Oct 30 02:10:26 EDT 2016

I ended up buying a pre-cooked Trimble plus a missilehead-like GPS antenna:


This should limit the chance it would be a DOA(well I hope at least), it 
comes already boxed, has somewhat a wide power supply voltage range, no 
pigtails to play with, and the antenna is new.

Now I just need to prepare the cable for the antenna, the mounting pole 
and wait them to arrive through snail mail.

Many thanks to all but especially to Larry McDavid W6FUB that helped me 
a lot to decide.

Now, while I wait...

1) I am reading the thread on EEVBlog(Thanks Bob and Bryan), (I have 
like one month before I receive the unit so I could have spent more, I 
admit) but I have several questions:

     a) Is this a board or a puzzle? seems that brings reverse 
engineering to a whole new level. 32 pages of forum posts looking for 
missing parts...LOL

     b) which is the difference between the Symmetrical and Trimble 
unit? I am mostly interested in interfacing, like the ability to get 
also NMEA sentences (if possible) and the ability to add the KOBB 
display. In the thread there    are a lot of information but really not 
sure how much is common between the two. Only sure thing I have 
understood seems that Trimble does not initiate a Survey at power on.

     c) since I *may* like to use the GPS antenna also for the clock 
kit(I WANT a DISPLAY!), I would like to build/buy a *simple* spitter. 
Just a second output. I hope that a passive cheap schematic would do. 
BTW, on which frequencies this unit receive data? Just 1575.42MHz? Would 
it be possible to build a Wilkinson splitter?

     d) still confused about the number of serial ports available, their 
expected usage and voltage levels.

     e) Which is the antenna signal level (dBm) that this unit require 
to operate properly?

Giuseppe Marullo

On 10/24/2016 1:05 AM, Giuseppe Marullo wrote:
> Hello Attila,
> not cheap at that point, and I already have that ST board(I live few 
> km from ST headquarters, BTW)!.
> Still licking my wounds from Eclipse-whatever chaintool, ouch, no way 
> I am going to mess with that again anytime soon.
> I am not in the mood to start another endless project, way too many 
> unfinished stull in my drawers(as many others I guess).
> I like the qrp-kit kit, but I will have a good look at eevb for the 
> "thunderbolt in disguise" and then I will decide.
> Thanks.
> Giuseppe Marullo
> On 10/23/2016 5:52 PM, Attila Kinali wrote:
>> On Sun, 23 Oct 2016 15:32:33 +0200
>> Giuseppe Marullo <giuseppe at marullo.it> wrote:
>>> I am puzzled about what to do, still the total cost of it for a OXCO +
>>> GPS(unit with antenna) + control mcu is 67usd, I doubt I could find
>>> anything like this for a cheaper price new.
>> Yes, it's cheap for a kit, but it is not that cheap if you want to be 
>> cheap. :-)
>> You can get GPS modules for as low as $5 on ebay (these are new),
>> a uC board for another $10-30 (even cheaper on ebay) and a quite good
>> OCXO for $10-30, also from ebay. A few wires, a bit of programming and
>> you have an GPSDO that beats the progrock. So, by buying the right stuff
>> you can stay below $30 and have something that will get you a long way
>> for experimenting.
>> Just for the fun of it:
>> http://www.ebay.com/itm/STM32F030F4P6-ARM-CORTEX-M0-Core-Mini-System-Development-Board-5V-3-3V-/371769616187?hash=item568f32273b:g:seAAAOSwXeJYCx63 
>> $1.40
>> http://www.ebay.com/itm/MCP4725-I2C-DAC-Breakout-Development-Board-12Bit-Resolution-/401209928223?hash=item5d69f9aa1f:g:j5gAAOSw34FVH5b1 
>> $1
>> http://www.ebay.com/itm/Aircraft-Flight-Controller-w-Ublox-NEO-6M-GPS-Module-for-Arduino-APM2-/182318966076?hash=item2a730ea53c:g:QuoAAOSwOVpXc3K~ 
>> $5.04
>> http://www.ebay.com/itm/1-USED-ISOTEMP-OCXO-143-141-10-MHz-5V-SC-CUT-Square-Wave-Crystal-Oscillator-/331997554003?hash=item4d4c98a553:g:w~sAAOSwCGVX~g24 
>> $16
>> Total cost: ~$25 including shipping and all but the OCXO are new.
>> You will need programmer for the uC board, if you don't have that, 
>> change
>> the uC board for an STM32F0DISCOVERY board:
>> http://eu.mouser.com/ProductDetail/STMicroelectronics/STM32F0DISCOVERY
>> Of course, any "real" GPSDO will beat this one by orders of magnitude
>> in phase noise and stability, but they are also much less fun to 
>> build :-)
>>             Attila Kinali
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