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

Didier Juges shalimr9 at gmail.com
Fri May 18 09:15:47 EDT 2018


A shield will definitely help with differential mode noise (the USB
communication signal) but has little effect on common mode noise (the
digital stuff coming from other parts of the circuit), a choke is the fix
for common mode (if you can't get rid of the noise at the source, or
otherwise return common mode noise directly back to earth instead of
through the cable).

Didier KO4BB

On Fri, May 18, 2018, 8:10 AM Clint Jay <cjaysharp at gmail.com> wrote:

> 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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