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

Dana Whitlow k8yumdoober at gmail.com
Fri May 18 08:16:18 EDT 2018

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

So please don't just assume that using a USB cable for charging only solves

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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