Re: star coax network with rj adapters ?

On Fri, 05 Dec 2008, in the Usenet newsgroup comp.dcom.lans.ethernet, in article
<ghc51l$nn5$1@xxxxxxxx>, Glen Herrmannsfeldt wrote:

It is theoretically possible to do with a transformer, but
the impedance has to be pretty closely matched. It has worked
for telephones for many years now. Newer phones may do it with
active circuitry, but older ones used a special transformer.

The phone design leaks some of the signal back to the receiver,
as it makes people more comfortable.

For a coaxial Ethernet, the collision detection depends on having a
very high return loss, which translates to a very low VSWR. I don't
believe this was specified directly, but a 1.08:1 (26 dB return loss)
was starting to push things.

Easiest for current technology, where wireless is out of range and
coax is available, is to take the center conductor of the coax and
wrap it around a wireless adapter. The coupling doesn't need to
be large for it to work.

Hmmm.... transmit power +20 dBm max, receiver sensitivity for 10 MB
about -80 dBm - so total available loss is 100 dB max. 802.11 is at
2.4 to 2.48 GHz, and single braid coax is really out of range at those
frequencies, but the insertion loss of RG-58 is about 40 dB/100 feet.
Sure hope the coupling is relatively tight, or you aren't trying to go
very far. I wouldn't even bother trying with a 5 GHz wireless.

Old guy
.

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