> On Aug 17, 2015, at 4:06 AM, Bob Camp <[email protected]> wrote: > > >> On Aug 16, 2015, at 9:40 PM, Nick Sayer <[email protected]> wrote: >> >> >>> On Aug 16, 2015, at 6:04 PM, Bob Camp <[email protected]> wrote: >>> >>> Hi >>> >>> Here’s some of the “that depends” questions: >>> >>> What is your stability goal? >>> >>> You talk about the NIST numbers on GPSDO’s. What level of stability are you >>> after? >> >> I believe I’m at or better than the stability I originally sought. Part 1 of >> my question is whether that’s actually true or whether my naivety is >> presenting me with a delusion. Part 2 is whether the price point at which >> I’ve arrived will support the level of stability I’ve achieved, or am I >> delusional in thinking people would or should pay what I’m asking for what >> I’m offering. > > The stability can only be verified by careful testing, The design goal > (what’s the spec) will in many ways determine > what sort of testing you will need to set up. A 1x10^-9 design would be > tested differently than a 1x10^-13 design.
10^-9 was the target all along. Question number two that I came with was whether or not it was reasonable to ask $175 for 10^-9. > >> >>> >>> What is your end application? >>> >>> Is this intended as a lab standard, the reference for a radio, something >>> else entirely? >> >> A low cost lab standard is what I have in mind. A box you can sit on your >> workbench with 3 BNC jacks that can feed 10 MHz into your frequency counter >> or what not. > > Do you anticipate any phase noise sensitive instruments being attached? Most > frequency counters are fairly simple. I stared with an immediate need, and that was for low frequency testing with sample times in the 10^1 range, so phase coherency has not been anything I’ve been concerned with. The Connor Winfield phase plots at the low end look “good enough” to me, and with a 370 ppt DAC granularity, I can’t ask for a lot of phase coherency at the high end (you can see that in the time lapse videos). > >> >>> >>> What is the destination? >>> >>> Is this heading towards a commercial venture or is it a basement project? >> >> I’ve entered it in the “Best Product” Hackaday 2015 prize contest. That >> said, I have no intention of attempting to compete with the established >> commercial firms in this space. I want to stay at around a Q:100 unit cost >> of around $75, which is where it is right now (the retail price is higher at >> the moment because I’m not manufacturing them in Q:100 lots yet). > > Ok, so have you taken a good look at your costs and return? Do you have an > method set up for > support of the product and for handling returns / repairs? Overhead costs > that do not get factored > in early can be very painful later on. Yup. The rule of thumb I have always used is that retail price is double the cost. That’s why I talk about a Q:100 cost of $75 and am charging $175. $175 is not $150 because I am not yet at Q:100 build costs, but that is the eventual goal. > >> >>> >>> What is the budget? >>> >>> Do you have $200K to spend on this? Did the piggybank run dry at $100? > > > For a commercial venture this is a very important factor. You don’t have to > share > the info, You do have to work out a number. > >>> >>> What is the timeline? >>> >>> Does the project complete at the end of the summer, no matter what? Is it >>> something that is worth another year or two of effort? >> >> I’ve got something now, but I don’t mind revving it to improve it, as long >> as the budget doesn’t change a lot. A lot of suggestions so far have >> centered around improvements that could be made regardless of budget. Like >> I’ve said, I don’t want to try to compete with Trimble. > > I would suggest that you figure on quite a bit of your spare time going into > this. That never happens. :) > >> >>> >>> What is your background? >> >> Mostly software, but in the last few years I’ve become reconnected to my >> nascent hardware side. I’ve been selling stuff in my Tindie store for a >> while now - a fairly eclectic mix of different projects that interest me. >> What led me to this project was another one - my Crazy Clock. I discovered a >> rather embarrassing design error that was causing errors on the order of >> dozens of ppm (I expected under ten). The first step in coming to grips with >> that issue was determining its scope, and that meant an extremely accurate >> low frequency counter, and that led me to needing a frequency standard. But >> I don’t have any way to test something I buy off eBay, so I wanted a GPSDO. >> But I couldn’t find any that weren’t way out of budget, so I set out to >> design one. And because I figured I wasn’t the only maker that needed >> something like this, but didn’t have the need or budget for something 2 >> orders of magnitude better, I thought I’d try this. >> >> Now where I am is trying to determine if I am correct in my assertions, and >> if my cost-benefit analysis of this as a product makes sense or not. > > > That’s what the market will tell you …. > >> >>> >>> Does all of the stuff we’ve been tossing around make perfect sense? (= you >>> do >>> something like this for a living). Are we talking about a bunch of stuff >>> that makes >>> very little sense? (= you are just getting started at this sort of thing). >> >> No, it’s all perfectly sensible. > > Ok, so here’s the next layer: > > If you are selling a frequency standard, most of your customers will probably > be > interested in it’s frequency stability. Unfortunately this opens a major can > of worms > spec wise. There are a number of measures that characterize various types of > noise. None of them directly address “if I measure 1.23 x10^-10 is it > correct”. You > see numbers like “< 1x10^-10 99% of the time” in spec sheets. > > If you dig into the archives, you can find numbers posts from people who are > disappointed that their "1x10^-13 GPSDO” can not deliver a 1x10^-10 frequency > measurement 99% of the time. Ok, well, with the advice I’ve gotten so far here I’ve decided I am going to see if I can afford a TimePod and I’m going to try and get one of those FE-5680A rubidium standards off eBay. If that works out, then my perception (correct me if I’m wrong), is that that will be enough to characterize 10^-9 levels of expected performance. I’ve also mailed a unit to a kind volunteer here who said he’d take a look at it. If his opinion differs wildly from what I think is the current state of affairs, then I can stop and take a serious look at whether a new design would be able to better reach the same goals with the same pricing. > > >> >>> >>> Each of these twists and turns heads you off into a different set of >>> further issues and >>> likely some more questions. For a commercial venture, buying custom >>> oscillators in >>> bulk is a very normal thing to do. For a battery powered balloon carried >>> reference, you >>> do things different than for a rack mount standard. Each of these projects >>> people come up >>> with have its own unique drivers. >>> >>> Each of us in our replies, tries to guess what your constraints are or are >>> not. In doing >>> so we likely substitute our constraints for yours. The further our >>> constraints diverge from >>> your constraints, the further off base our advice and answers will be. >> >> I appreciate that. I came here with a narrow question in mind, but perhaps >> it wasn’t the correct one. > > There is only so much you can pack in a single message … > > Bob > >> >>> >>> Bob >>> >>> >>> >>>> On Aug 16, 2015, at 3:39 PM, Nick Sayer via time-nuts <[email protected]> >>>> wrote: >>>> >>>> >>>>> On Aug 16, 2015, at 12:31 PM, Tom Van Baak <[email protected]> wrote: >>>>> >>>>> Anyway, to answer your question -- to measure its true performance you >>>>> only need two things. 1) a phase meter (or time interval counter) that's >>>>> good to 1 ns or better, and 2) a local reference standard that's maybe >>>>> 10x better than the TCXO and the Adafruit GPS. Usually that means a >>>>> cesium standard, or supremely qualified GPSDO, or equivalent. >>>> >>>> I have a frequency counter, but it’s not a phase meter. I have a scope, >>>> but I assume that trying to use a ruler with scope traces isn’t the >>>> textbook way of doing that. :D >>>> >>>> I have considered in the past buying a used rubidium standard off eBay, >>>> but have hesitated because I don’t know how much life there is left in the >>>> tube, and I just have to take it on faith that it’s stable and accurate. I >>>> have somewhat more faith in the GPS PPS, but clearly that has limits. >>>> >>>>> >>>>> A number of us here on the time-nuts list have such equipment at home. >>>>> And unlike professional labs, we will do it for free/fun if you loan the >>>>> GPSDO for a week. >>>> >>>> I will happily *give* one to someone if they would be willing to help a >>>> relative newbie with this stuff. >>>> >>>> Just one though. They’re kind of expensive to build. :D >>>> >>>> _______________________________________________ >>>> time-nuts mailing list -- [email protected] >>>> To unsubscribe, go to >>>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts >>>> and follow the instructions there. >>> >> > _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
