[Top][All Lists]

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

Re: [Discuss-gnuradio] Power line communications

From: Patrik Tast
Subject: Re: [Discuss-gnuradio] Power line communications
Date: Wed, 22 Feb 2012 00:33:51 +0200

Hi Johnathan,

The 125MHz interferece (AC) sounded familiar to me so I dug in the archives.
The image below is received at 137MHz @ Los Angeles and they have the
AC lines dangling in the air like a spiderweb. When it gets rainy we see those 125MHz in our images.
The antenna was ~20m avay from the AC lines

The format is APT (Automatic Picture Transmission) from polar orbiting NOAA satellites.
One pixel line is 2080px wide and transmitted every 0.5 second.

So, from the image http://www.poes-weather.com/~jerry/apt/logs/daily/images/img_001.jpg it is easy to calculate the interference

image width = 2080px = 0.5 seconds
interference width ~34px = X seconds


----- Original Message ----- From: "Johnathan Corgan" <address@hidden>
To: "George Nychis" <address@hidden>
Cc: "GNURadio Discussion List" <address@hidden>
Sent: Tuesday, February 21, 2012 20:55
Subject: Re: [Discuss-gnuradio] Power line communications

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 :-)


Discuss-gnuradio mailing list

reply via email to

[Prev in Thread] Current Thread [Next in Thread]