[TriLUG] PLC and radio interference

[Tanner Lovelace]

On Monday, May 12, 2003, at 10:50 PM, Greg Brown wrote:

> I was checking out a neato article on slashdot about the nocat guys 
> setting up a wireless network using ethernet over power cable to a 
> small ether-over-power to 802.11 bridge.  This looked very 
> interesting.  The article is here:
>
> http://www.oreillynet.com/pub/h/352
>
> And the ether-over-power to 802.11 bridge is here:
> http://www.speedstream.com/products_powerline.html
> (the Speed Stream 802.11 bridge)
>
> Ether over power seems to be limited to 14 meg/sec, which is okay if 
> all you are doing is 802.11b which is 11 meg anyway.  Now, the 
> question is related to propagation of the ether signal over the power 
> cables.  I'm NOT a EE, nor someone with much of any experience with 
> power other than as a two-year-old I learned that if you chew on a 
> metal key then plug it in, you get a funky burn on your arm that never 
> goes away.
>
> Now, my question is how far does the ether signal travel over the 
> power cable?  If this type of thing works as claimed then the ether 
> signal must hit the main breaker panel in the house (it has to if it's 
> going from one circuit to another) and if it hits that panel does it 
> propagate out via the main power circuit to the house then possibly to 
> the neighbors houses?  I would imagine that the signal is fairly 
> limited in distance but if you've got a 200 amp circuit coming into 
> the house that copper has to be of fairly large gauge which would 
> allow the signal to travel farther (kind of like 10-base-5 vs 
> 10-base-2 (or 10-b-t for that matter)).  And if you can blast 14 meg 
> over 15 amp wires how far can you shoot a signal down a 200 amp wire?
>
> Any thoughts here?  Could it actually be possible to hack a neighbor 
> (or at least sniff) over the power lines in the 'hood?
>
> I'm sure this is providing someone with a good laugh, but like I said, 
> I'm not EE.

Typically access PLC (power line communications) can go for up to 1km. 
You can get longer
ranges, though, by adding hubs every km or so.  The big problem here, 
though, is that
the carrier is in the HF bands (typically 4-50Mhz) and the power lines 
are far enough
apart to act as extremely good antennas.  This means that the potential 
for harmful
RF interference is substantial.  As it stands right now, both companies 
and users
are responsible for making sure the interference doesn't happen.  
Unfortunately, the
companies tend to say the users should do it, then they don't turn 
around and tell
the user that they're supposed to mitigate interference.  Then end 
result is that
HF radio propagation may be severely impacted.  So, before you deploy 
ethernet over
power lines (and potentially alienate your friends in TriLUG who are 
getting their
ham radio licenses), please investigate all the details.  See this web 
page for
more details including detailed studies of the interference problems:

http://www.arrl.org/tis/info/HTML/plc/

Tanner Lovelace
KB4TYE