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

David Lord snews at lordynet.org
Fri Aug 28 16:48:29 UTC 2009


David J Taylor wrote:
> 
> "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

That's the one I looked at but not understood latter part was
back to lan.

> 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?
> 

That was plan A but I found one in my bag of adapters and don't
think I ever used it but at least the adapter is seen by NetBSD
so I may try with the GPS or just wait another couple of days to
use the Conrad/MSF.

Via mobile broadband the clock would be best synchronised by
ntpdate and if lucky I'd be within a second so even +/- 2ms
would be a massive bonus.

I've been trying to sort out why a tgz file downloaded via
Vodafone mobile broadband is much larger than the source file
and already worked out the downloaded file has been decompressed
and verifies as a tar file. Others have reported same with zip
files being corrupted. Anyway having megs of log files to go
through comparing timestamps hasn't helped when I've found I'm
minutes out and ntpd on netbook had just given up, as does
chrony.

cheers

David




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