[time-nuts] Bodnar "Precision Frequency Reference (GPS Clock)" AND LeoNTP Networked Time NTP Server Questions

Clint Jay cjaysharp at gmail.com
Fri May 18 09:09:52 EDT 2018


Interested to know how much noise would be from USB signalling and how much
is " machine noise"  from the PC as my understanding of USB signalling is
that it's differential so such should be low noise?

I'm also not sure I've ever seen a non screened usb cable?

On Fri, 18 May 2018 1:17 pm Dana Whitlow, <k8yumdoober at gmail.com> wrote:

> Caution, folks, about USB cable radiation.  While the intended signals
> flowing through the
> cable presumably contribute a bit to the overall picture, common-mode
> currents on the cable
> are the most likely cause of severe radiation problems.  These currents
> arise not merely from
> intended USB signals, but from *all* the digital activity within the
> device, and will be present
> whether or not USB communications are going on.
>
> The keys to controlling this problem are:
>
> 1) Shielding on the USB cable.
> 2) Proper design inside the USB device, rarely done beyond the point of
> (barely) meeting
>      government regulations, which are far too forgiving IMHO.
> 3) Use of a ferrite choke on the cable to reduce those residual currents
> that get by anyway.
>
> Note that only item 3 might be under the control of the user to any useful
> extent.
>
> So please don't just assume that using a USB cable for charging only solves
> anything.
>
> Note that the above comments are also generally applicable to *all *cables,
> including power
> cables, that are plugged into *any* digital device.
>
> Dana    K8YUM
>
>
>
> On Fri, May 18, 2018 at 5:15 AM, David J Taylor via time-nuts <
> time-nuts at febo.com> wrote:
>
> > Anyone who is using one (or both) of these, and/or folks who have a
> > logical opinion:
> > []
> > There's more...  but this is a good start.  Just want to try and get
> > parts on the way.  Have to build a separate outboard regulator for the
> > timing GPS antenna, too.
> >
> > Thanks!
> >
> > Clay Autery
> > =============================
> >
> > Clay,
> >
> > I have all three of these units, all powered off USB.  I don't see any
> > reason why you shouldn't use a USB cable with just the DC part connected,
> > so that there's no issue about radiation.  A standard USB port would only
> > supply 0.5A so that's an upper limit on the power consumption.  If it's a
> > very long USB cable (you mention mast-head) check the resistance.
> >
> > As a crude guide...
> >
> > - The (larger box) NTP server feels cold to the touch.
> >
> > - The smaller, single output frequency source feels very slightly warm to
> > the touch (feeding an Icom IC-R8600)
> >
> > - The larger, dual-output frequency source feels slightly warm to the
> > touch.
> >
> > There's an e-mail address where you could ask:  support at leobodnar.com
> >
> > Cheers,
> > David
> > --
> > SatSignal Software - Quality software written to your requirements
> > Web: http://www.satsignal.eu
> > Email: david-taylor at blueyonder.co.uk
> > Twitter: @gm8arv
> > _______________________________________________
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> >
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