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

[David Bengtson]

I only have 60' to 80' of separation, so not too far. WIth good cable,
the cable losses are manageable. F/O cabling would be helpful to avoid
ground loops but would add a fair amount of complexity


Dave

On Sat, Mar 25, 2023 at 5:01 AM Dana Whitlow via time-nuts
<time-nuts at lists.febo.com> wrote:
>
> What's wrong with fiber optical distribution?
>
> Dana
>
>
> On Thu, Mar 23, 2023 at 9:54 PM John Miles via time-nuts <
> time-nuts at lists.febo.com> wrote:
>
> > > Has anyone run across any publications on best practices or examples
> > > of 10MHz Lab wide distribution networks? I'm looking for a discussion
> > > on how to physically locate oscillators/distribution amplifiers, cable
> > > types and runs, RFI mitigation etc. I haven't come across any, and I'm
> > > starting to build one at work. We've got a Cs oscillator and I'd like
> > > to make sure we deliver that performance across our systems lab.
> >
> > A lot of things can be said in favor of low-noise distribution amps with
> > good VSWR, good channel isolation, and good PSRR (not so fast, HP 5087A.)
> > But over the years, I've learned that the three most important factors when
> > it comes to piping 10 MHz signals around are:
> >
> > 1) Shield resistance
> > 2) Shield resistance
> > 3) Shield resistance
> >
> > I've spent a lot of time recommending double-shielded coax in the TimeLab
> > manual and elsewhere, and I still stand by that advice, but what I've come
> > to realize is that this is really just a proxy for low shield resistance.
> > Good grades of single-shielded cable are basically as effective at HF as
> > double-shielded cable.  To the extent your cable ground shield exhibits
> > resistance, it's not a shield, it's a resistor.
> >
> > Avoiding ground loops is on the list too, but further down.  Never lift a
> > ground to avoid a ground loop.  Use coax-to-coax baluns only when you can
> > see a beneficial effect.  Focus instead on providing a shared
> > low-resistance
> > common ground  to your entire network -- ideally not the ground all the way
> > back at the service entrance -- and rely on low shield resistance on the RF
> > side to do the rest.
> >
> > Every installation is different and your mileage will most certainly vary,
> > but this is my take on it.
> >
> > -- john
> >
> >
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