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

Bob Camp kb8tq at n1k.org
Sat Oct 22 20:29:33 EDT 2016


The bigger issue with doing a “home brew” OCXO is getting crystals with 
known turn temperatures in a reasonable range for the project. Yes, you 
can build gear to do temperature runs on crystals and sort bags full of them. 
It’s likely that your whole bag of 5,000 came from the same bar and your 
net result will all look a lot alike…..


> On Oct 22, 2016, at 8:18 PM, Attila Kinali <attila at kinali.ch> wrote:
> On Sat, 22 Oct 2016 10:34:53 -0400
> Tim Shoppa <tshoppa at gmail.com> wrote:
>> I just went and visited their website, and see they also offer a "kit OCXO"
>> from mostly through-hole parts and PCB. The OCXO insulation box is made out
>> of PCB, the thermostat is simply a jellybean TO92 transistor, and the 27MHz
>> crystal is an AT-cut being operated around 45C, so nothing awful
>> time-nutty, but still pretty neat that it's a kit. Details at
>> http://qrp-labs.com/images/ocxokit/ocxosynth_assembly.pdf
>> show that it walks about 14ppm during warmup and then might be good to a
>> ppm or so.
> It's funny how you can tell from the transistors used, where the designer
> is from (BC547 -> European :-)
> Kits like these have been around ever since I remember. This is one of
> the better ones, where the crytal isn't just soldered to some transistor,
> but a whole "insulation box" built around it. In german we call these
> things "Quarzofen" (lit. "quartz oven") and that's IMHO a very precise
> description what they are :-)
> Generally it's not very difficult to build some kind of temperature
> stabilization system. Heck, just using a heater transistor with a
> constant current through it will give you a more stable temperature,
> even if you don't control the current other than keeping it constant.
> Puting some form of box around it that restricts air and thus heat flow
> will make it even better. Using some temperature control and you are
> within 1-2°C of stability and way better than most hams need.
> The difficulty starts when you need more than that, when you need
> temperature stabilities below 1°C, when you want to keep it stable
> to 1mK or even below that.
> BTW: If anyone has recomended texts on how to build stable ovens
> for crystals, I'd like to hear about them. I've alread had a look
> at what Rick Karlquist wrote, but I would also like to read more.
> Unfortunately, good stuff literature is, as often, hard to find.
> On Sat, 22 Oct 2016 17:04:19 -0400
> "William H. Fite" <omniryx at gmail.com> wrote:
>> You need to catch up on what hams are REALLY using.
> What hams have been using varies a lot. As much as what time-nuts are using,
> or probably even more. I know a few people who still build valve PAs because
> they are "indestructible" (aka can take a lot of abuse without damage).
> But I also know people who do designs that are at the border of what
> is technically possible today.
> 				Attila Kinali
> -- 
> Malek's Law:
>        Any simple idea will be worded in the most complicated way.
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