[time-nuts] Raspberry Pi NTP server

[jimlux]

On 7/4/20 7:49 AM, David J Taylor via time-nuts wrote:
> David,
> 
> I've seen your comparison in the list archives. However, none of the
> approaches I have seen published so far (including yours) exploit all the
> possibilities I mentioned.
> 
> The Raspi having better community support doesn't help if the platform 
> itself
> is unfit for the purpose. It might be OK as a general purpose NTP server if
> you don't have any special requirements to accuracy, but for a PTPv2
> grandmaster, having the ethernet behind a USB interface is a no-go.
> 
> Regarding the RF interference - I'm running a Ublox M8T module directly
> mounted on the BBB via my custom GPSDO cape. It is working just fine.
> Disabling the onboard HDMI encoder might be the "secret sauce" for success.
> 
> BR,
> Matthias
> ===================================
> 
> Matthias, my feeling is that if you want a precision source, neither BB 
> not the RPi is a good solution.  Maybe with all the tweak you mentioned 
> the BB approaches precision (for some values of precision).  I see the 
> RPi as something which can provide far better NTP than simply using an 
> Internet source, something which will be adequate for the majority of 
> users (for some types of user!).
> 
> The RPi 4 doesn't have E/net over USB hence my comment on seeing a 
> comparison.  The RF interference is to other parts of the spectrum - not 
> specifically 1.5 GHz GPS - and has been documented.  I noticed it on 
> either 145 or 435 MHz bands when testing.  [Jim] Whether anyone has 
> bothered to do proper measurements I doubt.
> 

I was wondering more about non-GPS band interference.. And whether 
anything was hooked up to it.

I've got some RTL-SDRs here, and I've connected them both to an older 
RPi and some BBs, and with a whip antenna about a meter away, I've not 
noticed a huge difference between them, in a sort of casual way. They're 
both noisy, but then, I don't know if it's the environment, or other 
stuff hooked up to them (Ethernet or USB cables, or the USB power supply).

I wouldn't expect them to be hugely different from an RFI standpoint as 
bare boards with nothing else connected. It's stuff that's connected is 
more likely the source, by conduction from the board then radiation from 
the wires. That's why I was asking about the details.