I am a relative newbie here myself, but at the risk of starting a firestorm, I would take issue with some of what Bob says below. See comments interspersed.
On Wed, Jan 27, 2016 at 7:43 AM, Bob Camp <kb...@n1k.org> wrote: > Hi > > Ok, so let me answer the questions you *should* have asked: > > (They are in no particular order. Number 3 probably should come first) > > 1) Is the gear I have enough to do this project? > > No, you will need some sort of frequency / time standard. An atomic > clock of some sort is pretty much a minimum. You probably also need > a working GPSDO (or set of them) for comparison as well. You will also > need a working / modern precision counter that will give you data down > in the < 100 ps range. > This depends on your answer to #3 below. For my GPSDO, project, all I have is a scope, DMM, and PC. I can't measure ADEV, but by setting the time constant of my filter to 1000 sec and monitoring the TIC output I can be pretty certain that my local reference is well within 100 nsec of the "true" time. > > 2) How will this ultimately be built? > > At the very least, you will be building this with surface mount devices. > If it’s a scratch build, you will be dealing with fine pitch parts. That > gets > you into a whole bunch of gear. It also gets you into a very real “is this > fun or not” sort of question. > For my GPSDO I started with and Arduino board and a solderless breadboard. Anything with an SMD is on a purchased breakout board that spreads its pins to 0.1" centers. You do have to be careful to keep the wires short when working with fast rise times. I migrated this to a solder-type breadboard that mimics the layout of the solderless board and it is working fine. > > 3) What *is* the goal? > > "I’m going to make dinner” is the start of a process. It’s not enough of a > goal to accomplish the task. Starting the task with a general objective is > fine. > It does need to be refined a bit before you go much further. > Agreed. > > Is this what most of us would call a GPSDO (self contained box) or is it > something with a PC in the middle of it? > Mine runs either stand-alone or with a PC to monitor it. > > Is this an OCXO based “precision” device or is it something more simple? > I used a $25.00 surplus OCXO. Eventually I may invest in something better but then I would have to get a timing GPS to go with it. Currently I am using the $40.00 Adafruit module. > > Is a pure software solution good enough? > Mine is almost all software, but it has a TIC that consists of a 74HC4046 phase detector chip, a diode, a cap, and 2 resistors, feeding an A/D input of the Arduino processor board. This gives a resolution of 1 ns. > > Each of those decisions (and that’s by no means a full list) will send you > off > in a very different direction. > For sure! > > 4) How long is this likely to take? > > Best guess based on the others who have done the same thing - several > years. > I have been at it on and off for about two years but I have learned a lot along the way. > > 5) How much is this likely to cost? > > If done the way others have done it, several thousand dollars up to > quite a bit more than that. > My total investment (not including the scope, DMM, and laptop PC) is under $200. > > 6) How much research is involved? > > Quite a bit. The information you need is scattered all over the place. > Figure > that you likely will read at least several hundred papers. There is a whole > statistical language that is unique to these gizmos. This is *not* a > follow a > set recipe sort of project. > Again, depends on your answer to #3. I started with a working design and code and modified it to suit my fancy. I am pleased with the result. It keeps the brain cells firing. > > Lots of fun !!! > Absolutely!! -- --Jim Harman _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.