Re: [Discuss-gnuradio] Power line communications

[Johnathan Corgan]

On Tue, Feb 21, 2012 at 10:18, George Nychis <address@hidden> wrote:

> Wow... so let me make sure I get this straight.  That's just a passive
> reading of the RF spectrum on your wall socket... you are not introducing
> any form of transmission on the line?  The USRP N210 was simply just plugged
> in to the power strip, right?

As I mentioned in another email--the loud signals were my logic
analyzer probe radiating the 125MHz and 100MHz clocks from the USRP
N210 and being received by the power line.  Once I unplugged the
cable, those spectral lines went completely away.  Actually, the USRP
N210 was pretty quiet considering the case was off.

But yes, both spectrum analyzer plots were passive measurements of the
building power infrastructure coupled to 50 ohms.

> If so, that's unbelievably noisy.  I didn't expect it to be *that* bad.  The
> FM stations are definitely clear.

Yep.  It's why we researched the DSSS technique, it works very well to
increase the SNR (at the expense of bit rate.)

> It's very hard for me to find specs of commercial power line equipment, but
> it typically operates between 2-28MHz?  Even within that short range, given
> your zoomed in snapshot, there is almost a 40dB difference in the amount of
> noise from across that band from valley to peak.

Yes, 2-28 MHz is typical.  Power lines have increasingly higher
attenuation above that; below that, transformer high-pass
characteristics come into play.  The zoomed in plot shows the
approximately 1 MHz corner of the coupler used.

I was, however, able to load up my house wiring through the coupler
with a few watts at 146MHz and successfully contact a local ham radio
repeater :-)

Johnathan