[ntp:questions] Radioclock connection via serial to usb adaptor on Linux or BSD?

David J Taylor david-taylor at blueyonder.not-this-part.nor-this.co.uk.invalid
Fri Aug 28 14:01:03 UTC 2009


"David Lord" <>
wrote in message news:7fpt7oF2irus6U1 at mid.individual.net...
[]
> Thanks for that info
>
> Your graph shows around +/- 2ms which is similar to what DCF77 gives
> me using PARSE driver and that just needs RxD that I suspect I'd get
> away with if I can make a small addon aerial that's a lot more
> sensitive than the ferrite supplied with the Conrad.
>
> Other than more expensive adaptors I can't see any specs giving
> details for serial to usb other than drivers for Windows supplied
> and at around 15 quid for an adapter I don't really want to blow
> that much.
>
> I'd swap mobile broadband provider but at moment Vodafone have best
> or only coverage around here (Rossendale/Calder valleys), but
> quality of the service is deplorable (we don't guarantee files
> won't be corrupted whilst passing through our network).
>
> David

David,

I think you may be confused by the multiple graphs on that page.  Perhaps 
the clearest is:

  http://www.satsignal.eu/ntp/2009-05-20-21-22-narvik_ntp-b-day.png

which shows a switch /from/ serial-GPS over USB /to/ a LAN connection to a 
stratum-1 server.  With the GPS/USB combination, the offset is about +/- 
400 microseconds.  The +/- 2 ms is with the LAN connection, not the USB. 
My tests were done because of the myth which had been perpetuated here for 
some time that USB was useless, with no indication of what performance 
might actually be obtained.  I would expect even better performance with 
FreeBSD.

It does seem to be pot luck as to how good the drivers are, and perhaps 
whether the control lines are emulated.  Perhaps your best bet is getting 
a unit from a local shop on a sale or return basis?

Cheers,
David 




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