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

[Burt I. Weiner]

Gang,

I know this probably goes against good 
engineering...  I have two DATUM 9390 GPS Time 
and Frequency "standards" that I feed to several 
devices.  For distribution I use a Winegard TV 
splitter, the blue type in a metal case.  The 
Winegard splitter is mounted to an unpainted rack 
panel in my rack o' stuffs.  The output level of 
the DATUM standards is high enough so that the 
loss in the splitter is not a problem for the 
equipment I'm driving; at least nothing 
complains.  All of my cables are Quad RG-6U cable 
with F-Connectors.  The cables are on the average 
about 4 feet long, with one exception of a cable 
that is about 25 feet long.  At each receiving 
end I have F female to BNC male adaptors - I said 
this was not good engineering!  I use to have a 
Heathkit "Worlds most accurate clock" in my 
shoppe that often parked and worked on WWV-10 
without any problems.  I also have a few 
receivers, with an outside dipole antenna, that I 
can tune to WWV-10 and barely hear the 10 MHz 
from my standards and unorthodox distribution 
system.  I didn't expect the standard's 10 MHz to 
be non-existent in the receivers, but it's a lot lower than expected.

Burt, K6OQK


At 07:15 AM 3/24/2023, you wrote:
>Bob makes a good point about the devices 
>terminating the ends of reference distribution 
>cables.  Many frequency counters have little 
>shielding, and can be a significant source of 10 
>MHz radiation, regardless of the shielding 
>effectiveness of the reference cable runs 
>feeding them.  Counters such as the HP 53132 
>and 5335 are good examples of this.  Even some 
>signal generators and spectrum analyzers can 
>exhibit this problem.  Despite good shielding 
>in their RF sections, sometimes inadequate 
>attention was paid to shielding of the external reference inputs.
>
>I encountered this problem when building a 
>reference distribution system for my low phase 
>noise house standard.  The distribution amp was 
>meticulously shielded and double shielded cable 
>was used throughout, with runs up to 60'.  When 
>individually terminated, the cables showed very 
>low leakage.  However, significant 10 MHz 
>radiation resulted when connected to numerous test instruments...
>
>73,
>
>John K9WT
>
>
>On 3/24/2023 8:26 AM, Bob Camp via time-nuts wrote:
>>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 Â
.
>>
>>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 Â
.
>>
>>  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
>>>_______________________________________________
>>>time-nuts mailing list -- time-nuts at lists.febo.com
>>>To unsubscribe send an email to time-nuts-leave at lists.febo.com
>>_______________________________________________
>>time-nuts mailing list -- time-nuts at lists.febo.com
>>To unsubscribe send an email to 
>>time-nuts-leave at lists.febo.com 
>>_______________________________________________ 
>>time-nuts mailing list -- 
>>time-nuts at lists.febo.com To unsubscribe send an 
>>email to time-nuts-leave at lists.febo.com
>
>Burt I. Weiner Associates
>Broadcast Technical Services
>Glendale, California U.S.A.
>biwa at att.net
>K6OQK