[time-nuts] Re: 10 MHz Distribution Best Practices?

[David Bengtson]

I've come across this document

audiosystemsgroup.com/RFI-Ham.pdf

which is a good compilation of RFI minimization focused at Ham
operators, so focused at HF frequencies (Sub 30 MHz) so pretty
relevant.

Dave

On Sat, Mar 25, 2023 at 5:04 AM ed breya via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> As always on this subject type, I must comment on the utility of
> managing ground loops with common-mode chokes on cables between
> equipment. I think this is the simplest, most beneficial thing you can
> do for good quality signal distribution.
>
> Good cables, shielding, and grounding are all fine and good, but do not
> address the ground loop currents that inevitably flow between any
> interconnected pieces of gear. Adding CM chokes raises the common-mode
> impedance of the cable(s), greatly reducing the loop currents. You can
> see these parts all the time, inside equipment, or added or built into
> cable assemblies and such - almost always to fix EMC issues. The
> simplest are the clip-on type ferrites that are easily added to almost
> any cable type.
>
> These are mainly to suppress RF and HF emissions from SMPSs and digital
> circuits and such, but they can also be effective even for mains
> frequency (and harmonics) ground loop control, with the right cores and
> some simple tricks. The reason is that the voltage levels and impedances
> are quite low (millivolts and milliohms), so adding even a small
> inductive reactance can be quite effective, percentage-wise.
>
> If you have mains frequency ground loop problems, you can try cores with
> as high an A sub L as possible, and even better, multiple turns to get
> the squaring benefit. There are ferrites available that should do well,
> depending on the situation. I have even used regular silicon steel wound
> or laminated line frequency transformer cores as CM chokes in certain
> situations where very large line rejection was needed.
>
> For narrow-band distribution of 10 MHz for instance, another option is
> to use transformer coupling of the signal, so the low frequency ground
> current and interference is eliminated, and a high frequency CM choke
> can take care of the rest.
>
> Ed
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