10base5 (Thick) Terminator ?

Pete Turnbull pete at dunnington.u-net.com
Thu Mar 31 16:20:51 CST 2005


On Mar 31 2005, 14:38, Tom Peters wrote:

> It was (is-- I still have a spool of it!) 50 ohm coax with N
connectors,
> and paint marks at every meter boundary. You had to terminate each
run of
> thicknet end each end (that's two ends, for those who are counting).
>
> You had to tap it with a vampire tap ONLY ON THE 1 METER MARKS using
a tap
> drill tool that would core into the shield and expose the center
conductor.

Actually, every 2.5m, not every meter.

> I'm still looking for specs on thicknet cable-- I know the
characteristic
> impedance is 50 ohms, but if I knew the velocity factor and losses at
VHF
> (144 - 148 mhz) and UHF (430 - 450 MHz) I could use the stuff for my
> amateur radio hobby. As it is, it's gathering dust.

It varies very slightly from maker to maker and even batch to batch, so
if it's that critical you'll need to measure it.  Indirectly, the 802.3
standard says 0.78; my tables show Belden 9880 VF is 0.78-0.82, attn
1.3dB/ft @ 100MHz, 2.8dB/ft @ 400Mz, 4.5dB/ft @ 1GHz.  Sometimes people
use RG-8, though, which has VF 0.66, and higher losses.

Surely 144-148 millihertz is VLF, not VHF?

-- 
Pete						Peter Turnbull
						Network Manager
						University of York



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