> >
> > > Just moved into a new place, and along with all the cable tv coax
wiring,
> > > there appears to be couple runs of 75 Ohm "thicknet" coax
(10base5??). I
> > > would like to use this cable to connect a downstairs network to my
cable
> > > modem/router upstairs. Probably just a ReplayTV unit -- just for
the channel
> > > guide, not for streaming video.
> > >
> > > Is there any cheap way to do this? Some sort of 10baseT<->10base5
media
> > > converter on each end? Anyone know how, and where to get the
hardware?
"Thicknet" coax refers to the 10Base5 spec for data transmission, and to
the
type of wire that was used. 10 refers to megabits/second, the "Base"
refers to "baseband modulation" (the signal is at base band, using
DC voltage changes directly on the wire, and is not "broadband" which
is where the signal is modulated onto a carrier wave, as is done with
cable TV). Baseband carries just one information stream and broadband
carries many streams.
Finally, the 5 refers to 500 meters, the plysical maximum length of the
wire. Such an ethernet buss is bounded by two constraints, one is
the propagation delay of the wire which sets the maximum distance that
two nodes on the cable can be separated before the timing delay is so
great that any one station fails to detect the preamble from any other
station before tramsmitting, which can result in a "late collision"
where
two nodes keep transmitting after the preamble without hearing
each other. It doesn't really hurt anything but affects the backoff
properties.
Propagation delay of coax is typically 0.66 to about 0.74 of freespace.
The second physical bound is the electrical resistance of the cable
with the risk of signal loss being so great that two stations, again,
can't hear one another while transmitting, if at ends of the wire..
The 10Base5 cable is the same size as RG-213 or Belden 9913,
about 1/2 inch diameter. The 10Base2, much thinner, runs on RG-58
and is terminated with BNC connectors. The "2" means 200 meters max
length (actually 185 meters) because of the much higher attenuation.
10Base5 was terminated with N connectors. It has a solid copper
core, four braid laters and used clamp on taps (vampire taps) to
connect to the wire without cutting it. Look up the Cabletron ST-500
AUI tap device.
CATV wire is RG-6 or RG-59 and is 75 ohm impedance and is
typically terminated with F connectors. Ethernet wire is always 50 ohms.
CATV wire has a steel copperclad core for the center wire as it becomes
the center pin when you attach the F connector. CATV wire has
been referered to as 10Broad36 by the coneheads who invented
10Base5 etc.
You should not staple (or kink or sharply bend) Cat5 because any
disruption of the twist of the pairs can let the e-field extend past the
wire twist and possibly couple into adjacent pairs.
You should not staple TV coax because of the risk of breaking the
jacket and letting water intrude, as well as deforming the
shield to center spacing causing an impedance discontinuity.
Water is the bigger risk.
I would recomment ripping out all unknown wire and replacing
it with known good wire. NEVER use CATV wire for ethernet.
Coax for ethernet itself is obsolete.
Bob
-----------------------------------------------------------------------
This list is provided as an unmoderated internet service by Networked
Knowledge Systems (NKS). Views and opinions expressed in messages
posted are those of the author and do not necessarily reflect the
official policy or position of NKS or any of its employees.
This archive was generated by hypermail 2.1.3 : Fri Aug 01 2014 - 20:30:25 EDT