I've been rather mindful of the lack of off air frequency standards broadcast sources of late. Difficulties receiving the WWV shortwave broadcasts and their Russian equivalents making the use of such services somewhat problematical. Whilst I can receive the Radio 4 LW rubidium based 198KHz standard ok, this is rather cursed with programme content modulation making its use as a frequency reference a less than trivial task.
Since there have been discussions by the official bodies involved over their imminent demise as far as continuing such frequency and time standards broadcast services, I'm a little reluctant to invest time and energy into constructing a suitable reference source disciplined by such services.
I had considered creating a source based on the R4 LW 198KHz rubidium standard but its imminent ceasing as a calibration source, if not as a LW broadcasting station altogether, has rather put me off such a project, hence my interest in a GPSDO based solution as per the title of this thread.
To that end, I've researched several DIY GPS based projects, eventually homing in on the u-Blox series of GPS modules, notably the Neo-M8N for its built in flash storage and TCXO and its programmability of the 1PPS output to any frequency from .25Hz to 10MHz (and even a little beyond though its 48MHz TCXO makes the obvious 10MHz choice a rather jittery one compared to say 1, 2, 4 or 8MHz[1]).
Searching eBay for cost effective sources of these u-blox modules has led me to the following no name brand item:
Ublox-NEO-M8N GPS navigation signal amplify module for arduino Rasppery PI
The seller, though obviously yet another Chinese trader, does at least hold this stock in the UK, making free delivery considerably quicker.
At 21 quid delivered[2], it seems a pretty good bargain but the lack of detailed documentation on its use does rather beg the question in my mind as to whether this lack is simply on account the item needs nothing further than the data sheets from u-Blox and some basic programming skills (Raspian, Arduino or even Z80 assembly!). Presumably, the description, as sparse on details as it appears to my eye, must be more than adequate when it comes to this seller's intended market of Arduino and RasPi enthusiasts.
Basically, I'm asking whether this particular example is just what I need as a starter to a more fully specced DIY GPSDO project or whether I should be setting my sights a little higher?
As far as I can gather, I can simply use its 10MHz output directly (after programming the 1PPS pin to output 10MHz) for use as (an albeit jittery) 10MHz frequency calibration reference and look to combining it with an VCXO (ovened or not) as and when I get the urge to improve it into a respectable GPSDO calibration source. If I've got the wrong end of the stick over such a 'Quick Fix' solution as I've envisaged, you're more than welcome to correct my misunderstandings. :-)
[1] I'm thinking of using an NB3N502 14 MHz to 190 MHz (output) PLL Clock Multiplier chip to recreate a less jittery 10MHz from a 1, 2 or possibly even a 4MHz clock as a "Quick 'n' Dirty" 10MHz frequency reference compromise between using the 10MHz direct and the full blown disciplined 10MHz VCTCXO/VCOCXO option. [2] Annoyingly, both image options are the same single view of the item so the Chinglish description of micro-usb and antenna option details can't be verified too readily.From the image, it looks to be sporting a ceramic plate antenna on its underside and the only candidate for a 'micro-usb' connector alongside the ext active antenna socket doesn't seem to be quite the right shape, quite apart from its location seemingly, imo, being unusually close to an antenna socket (GHz separation of operating frequencies not withstanding).