> 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. > >> >> 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. > >> >> 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. > >> >> 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. > >> >> 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. > >> >> 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.
