I’m seeing a strange noise issue with my USRP. I have a simple antenna
fashioned out of a spool of wire connected to a LF-DC daughterboard with
no anti-aliasing filters. The USRP is connected to a laptop and powered
off it’s standard brick power supply. When the laptop is plugged into
mains, my am-demod gui shows a lot of noise in the spectrum and time
series; when I disconnect the laptop from the power socket to operate on
the battery this noise goes away. I have two images demonstrating the
I don’t believe I was seeing this in the recent past, however I recently
upgraded to Fedora 7, although I don’t see how this could be a factor.
You can see in the pic that the demodulated time series has a strong
content at roughly 120 HZ; this could be a power-supply induced issue
Hz supply harmonic). The odd thing is there is no noise at all when I
disconnect the antenna, so the noise does not seem to be entirely a
function of the power supply alone. I also do not see the noise at all
when using a desktop PC.
My supposition is there is some kind of interaction between the power
ripple coming from the laptop power supply and the circuitry of the
USRP, but I
have no direct evidence.
Any thoughts? Has anybody seen this also?
Eric H. Matlis, Ph.D.
Aerospace & Mechanical Engineering Dept.
120 Hessert Center for Aerospace Research
University of Notre Dame
Notre Dame, IN 46556-5684
Phone: (574) 631-6054
Fax: (574) 631-8355