[c-nsp] Cable runs

[Bill Wichers]

> We've used RG6 for DS3. It runs alongside a DS3 run of 734. Both work
> fine and are about 75 feet. DS3 is such a low frequency compared to what
> is usually run on coax that it shouldn't be too distance sensitive. If
> you do it yourself, get the 75 ohm BNC connectors (used for video and
> DS3), which are less common than the 50 ohm BNC connector (used for
> radios)

The problem is that at the lower frequencies, the CCS (Copper Clad Steel)
center conductor of RG6 and "normal" RG59 results in higher losses than
the BC center conductor of the 734 cabling. I would imagine the aluminum
shield on RG6 is also a bit more of a problem. On such a short run as 75
feet I would be surprised if the RGx cables showed any problems, but for
the longer runs it starts to be more of an issue. And I have to spec
"correct" cables for work anyway to avoid getting yelled at :-)

BTW, easy way to tell the 75 ohm connectors apart from the 50 ohm
connectors is that the 50 ohm connectors have a plastic insert around the
center pin, the 75 ohm connectors do not (although some have a very thin
shroud around the center pin itself). The connectors *do* make a
difference -- I've had DS3 circuits show errors until I traded out the 50
ohm connectors (installed by telcos sometimes!) with the correct 75 ohm
connectors. I don't trust the two-piece connectors either, always use the
three-piece connectors where the center pin crimps on the center
conductor.

     -Bill

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Waveform Technology
UNIX Systems Administrator