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

Clint Jay cjaysharp at gmail.com
Sun Dec 20 04:32:12 EST 2015


I once spent a very miserable but profitable weekend remaking a thin
ethernet network where the "installation expert" had stripped back 10B2
coax four inches and neatly separated core and shield,  heatshrinked them
into pigtails and then soldered them into panel mount BNC sockets.

He was outraged when I suggested his cabling skills weren't up to much,
insisting he had done many other installs like that and that it worked just
fine because his multimeter measured the correct termination resistance
from one end to the other.

The TDR and vastly improved network speed of course showed exactly how
wrong he was.
On 19 Dec 2015 22:00, "Poul-Henning Kamp" <phk at phk.freebsd.dk> wrote:

> --------
> 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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