[geeks] DiY Stratum 1 server

[Sridhar Ayengar]

Lionel Peterson wrote:
>> I'm looking for resources on constructing a Stratum 1 time server.
>> I've done a fair amount of my own research, so I think I have a lot
>> of the questions answered as to what's a feasible time source and
>> so on.  As far as I can tell, my best bet is a cheap GPS receiver
>> of some sort.  Of course, cheap is going to mean "does not work
>> indoors," so I'm specifically looking at one of the
>> cheap-n-cheerful Bluetooth GPS receivers that seem to proliferate
>> just now.  I could at the very least put that next to a window, or
>> even bolt it down somewhere outside.
>> 
>> I have three questions:
>> 
>> 1) Is the additional overhead of Bluetooth and USB going to make
>> such a device useless as a time source?
> 
> You are joking, right? What resolution are you loking for - time down
> to what seconds, 1/10? of second, 1/100th of a second?

If you're talking stratum-1, you're going to want timescales shorter 
than that.  You can easily achieve those sorts of precision with
a stratum-2 on a decent connection with low latency against decent
stratum-1s.

>> 1a) Assuming the former, is there some other reasonably feasible
>> way of getting GPS time sync?  Do I need to man up and run a bunch
>> of serial cable outside?
> 
> Wired is (IMHO) better - I'd get a plastic outdoor box (not shielded
> - duh!), install the GPS antenna inside it and run a wire indoors.

I wonder how big of a difference there is in performance between GPS and
CDMA?  I've observed a significant price difference, probably because 
CDMA signal is so much easier to receive.

>> 2) Could I be using something better that doesn't cost a small (or 
>> large) fortune?
> 
> Better than the resolution/accuracy of GPS? I don't think so - using
> GPS is orders of magnitude easier than managing your own time source
> (I have to believe).

It's not really that big of a deal to manage your own time source, if
it's something you find interesting.

> I plan on making my own time server using GPS time service as well,
> haven't gotten too deep into the research yet, but it seems just
> about any consumer GPS reciever with a serial/USB connection should
> suffice...

I wouldn't trust either RS-232 or USB, myself.  There are reasonably 
priced devices with synchronous interfaces, if you look.

Peace...  Sridhar