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[Jeremy Portzer <jeremyp AT pobox.com>]

On Mon, 2004-01-12 at 14:02, Sil Greene wrote:
> Jeremy,
> 
> I think you're getting slightly confused in the details... 

You're right, I replied a little too fast, sorry about that, but...

> 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).

No, I know the difference between the two.  Shielded twisted pair, which
was commonly used for Token Ring connections, does indeed provide
further protection from outside radition.  It still may be a good idea
in specific manufacturing environments where there is a lot of radio
noise.  But the twists in UTP wiring are still the primary way that
reduces emission or reception of radition, compared to untwisted wires. 
This is why wires with a higher twist-count are more desireable (Cat 5
has more twists-per-inch than Cat 3 for example) .

> 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.

Was he using a VoIP phone, or a traditional analog telephone that used
the UTP wiring (in which case we can't call it Ethernet)?

A VoIP phone, which I know he has but don't know if that's the one
described here, would certainly not get that kind of interference from
the contractor's Nextel phone in the ceiling.  Any interference would
cause Ethernet frame errors, or TCP transmission errors, and the packets
would not be transmitted.  This would be heard by the end user as
garbled words, dropped syllables, or pauses in the conversation.  I
don't know how an audible hum like that could possibly be imparted onto
a digitally transmitted signal.

I realize I slightly misread the direction of the interference, sorry
about that.

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

Regardless, I don't think that could happen if the phone was really an
Ehternet (ie, VoIP) phone.  But it could if it was an analog phone,
though I'd be curious to know what the contractor was doing in the
ceiling -- perhaps there was something else up there he was fixing that
caused the problem.  

> --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)
> .:
-- 
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| Jeremy Portzer        jeremyp AT pobox.com      trilug.org/~jeremy     |
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