[time-nuts] SMD TADD-1 distribution amplifier - seeking comments and suggestions?

Poul-Henning Kamp phk at phk.freebsd.dk
Sat Dec 19 21:11:03 UTC 2015


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In message <56757344.2020904 at rubidium.se>, Magnus Danielson writes:

>The isolation strategy says that the various equipments should only be 
>power grounded, as required for personal safety, and then have all other 
>grounding paths "galvanically separated" (thus, DC and power frequencies 
>separated in common mode).
>
>The mesh strategy says that you extend the grounding of the power ground 
>with additional grounding with every cable and additional grounding 
>cables.

Please bear in mind that there is a *huge* difference between
single-ended (as in: RF-Coax-BNC) and balanced (as in: Audio-Twinax-XLR)
for both of these scenarios.

While you can get away with the isolation strategy with balanced,
because you have high CMRR inputs, there is nothing to "take care
of" the ground potentials in the single-ended mode.

>As a reference, Ethernet is designed to work in an isolation BN setup, 
>[...]

That is actually a new thing, the original Ethernet was 1/2" coax
and ground-loops and lightning damage was the order of the day.

The main reason Ethernet went balanced was actually for fault
isolation (star-topology vs. bus) and signal quality (IT people
were horrible at "sharking" and crimping coax.)

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at FreeBSD.ORG         | TCP/IP since RFC 956
FreeBSD committer       | BSD since 4.3-tahoe    
Never attribute to malice what can adequately be explained by incompetence.



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