Internetworkers: http://www.ibiblio.org/internetworkers/

[Sil Greene <Sil_greene AT unc.edu>]

Jeremy,

I think you're getting slightly confused in the details... You're right 
about twisted pair, though note the difference between STP (Shielded 
Twisted Pair) and the more common (less expensive) UTP (Unshielded Twisted 
Pair).

Mark's phone conversation was carried out over the ethernet; it was 
another cell conversation that is posited as having caused the 
interference, since the cell transmitter was positioned in the ceiling 
near the ethernet run.

Thus, the theory was not that the ethernet interfered with the cell, but 
that the cell interfered with the ethernet.

--Sil, also not an e.e., but with no real plans (and only a vague, 
dissipating interest) in getting there one of these days.  :)


Reported 04.01.12 13:52 from Jeremy Portzer:
.:On Wed, 2004-01-07 at 13:35, Tanner Lovelace wrote:
.:> Mark Turner wrote:
.:> 
.:> > <radio geek talk>
.:> > 
.:> > It's quite possible that his phone was being used close to the CAT5 
.:> > cable my phone was using, since he was working in the ceiling. His 
phone 
.:> > may have interfered with the frequencies on the Ethernet cable.
.:> > 
.:> > </radio geek talk>
.:> 
.:> Ah, that makes a lot more sense.  I hadn't realized he was in the
.:> ceiling near the ethernet cable.  Of course, since we're using
.:> a weird form of VoE (voice over ethernet, since we didn't by
.:> the voice over IP module), it probably messed up the ethernet
.:> transmissions.
.:
.:Ethernet cables normally don't emit or accept any radiation, the
.:"twisted pair" nature of the cables dampens most radiation emission (and
.:also acts as a shield).  The more twists, the better.  Not saying it
.:isn't possible, but it's not likely.
.:
.:Here are some much more likely sources of interference:
.:Ballasts from flourescent light fixtures
.:El-cheapo light dimmer switches (not as likely to be found in offices)
.:UPS equipment
.:Improperly shielded CRTs (Computer monitors, TVs, etc)
.:Improperly shielded industrial equipment of many different types
.:
.:> Sure.  Just make sure you don't miss out on something worthwhile
.:> while being careful.
.:
.:Agreed with that.  Note that the interference that Mark was receiving
.:was interfering with his *reception* of the cell phone signal from the
.:tower.  It had nothing to do with the transmitting circuit which is the
.:circuit that could possibly cause any harm to human health.
.:
.:--Jeremy  (not an e.e. but working in that direction one of these days)
.:

-- 
"If you put your supper dish to your ears you can hear the sounds
 of a restaurant."  --Snoopy    (Charles Schultz 02-12-2000 RIP)
Sil_Greene AT unc.edu