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

[Bob Camp]

Hi

There are indeed multi year sort of courses (actually sets of courses)
that various folks put on about the EMI side of this. Unfortunately it does
quickly get pretty deep in theory and thus the long slog to get to this or
that level of the knowledge base.

How big is “work” and how big is “lab”? I’ve seen places that measured
the answers in kilometers. I’ve also seen places that had everything within
20 meters of everything else. What you do in one is profoundly different 
than another.

How many “destinations” do you have that need this or that? Again, some
will have an answer in dozens, for others it will be in the thousands or even
tens of thousands. 

What connects to those end points? If the answer (as noted earlier) is 
a bunch of ADEV / phase noise gear, that’s very different than more 
conventional test gear. Keeping the 10 MHz away from the DUT can be
a *very* big deal.

Like it or not, much of this has been decided for you. That piece of test
gear has a very normal BNC connector on the back of it. They are a
terrible thing for this, but that’s what you get. The cable you use is
going to mate with them. If you use off the shelf gear for the distribution, 
it also has BNC’s on it. 

Cable needs to be run from here to there. Loss is rarely an issue. Skin
depth vs the shield is very much an issue at 10 MHz. Foil as a shield is
useless in this case. Big thick multiple layers of braid is needed. That 
isn’t just a “get RG-400” sort of thing. It’s also who you get it from. The
expensive source may be the one ….

There is a tendency to overdo this kind of thing. Think through how
many endpoints you need. Cable up the reasonable minimum and 
see how it goes. Plan on a re-visit in 6 months and maybe again in 
12 months. Having a lot of cable to nowhere is a problem in a number
of ways ….

Fun

Bob



> On Mar 23, 2023, at 8:45 PM, David Bengtson 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.
> 
> Thanks
> 
> Dave
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