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Re: [Discuss-gnuradio] Power line communications

From: George Nychis
Subject: Re: [Discuss-gnuradio] Power line communications
Date: Tue, 21 Feb 2012 13:18:13 -0500

On Mon, Feb 20, 2012 at 6:32 PM, Johnathan Corgan <address@hidden> wrote:
On Mon, Feb 20, 2012 at 07:32, Johnathan Corgan
<address@hidden> wrote:

>> If you ever do this again, I would love to see some of the channels over
>> time.  I ordered some basic PLC equipment, but all I really have access to
>> are packets :P
> I'll try to grab a spectrum analyzer plot from my lab.

Below are two images of the RF spectrum as received through a power
coupler plugged into a wall socket in my office building.

The first is DC-500MHz:


The green line is the thermal noise floor in the RF bandwidth used
(the measurement setup has a NF of about 9dB).

There are no quiet parts of the spectrum, and many narrowband signals.
 FM radio stations are obvious around 100 MHz.

The 125MHz spectral line and 100 MHz harmonics go away when I unplug a
USRP N210 on the same power strip :-)

A zoom of the first 50 MHz:


It's pretty noisy all over.

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?

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

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.

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