28 May
2010
28 May
'10
7:40 p.m.
Dammit, Fons! I'm trying to get some work done today and go
off and nerd snipe me.....
On Fri, 28 May 2010, fons(a)kokkinizita.net wrote:
OK, here's my guess (standing on the shoulders of guys
like Neil)...
The signal is being amplitude-modulated by a 100 Hz
saw-tooth signal. This signal by itself produces a
tight frequency series in multiples of the fundamental
(i.e. 100, 200, 300, 400 Hz...) and constant
amplitude. When used to modulate the amplitude of the
input signal, it results in a peak at the input
singal's frequency... with symmetric, attenuated peaks
@ 100 Hz spacing (like the ones that you show).
If you change the frequency of the input signal, the
surrounding peaks will move with it to maintain a 100 Hz
spacing.
The 100 Hz (being 2x 50Hz, the power freq. in Italy)
suggests that it is probably related to some manner of
power supply. However, I have no theory why we're
getting 2x 50Hz (and I think I need one :-)).
That the signal is (or is approximately) a sawtooth wave
suggests a capacitor somewhere... either corrupting the
ground signal or creating a ripple in the DC power supply
(rectifier circuit or a broken voltage regulator). I would
probably start by checking the MOBO power supply.
-gabriel
p.s. Nerd Sniping... http://xkcd.com/356/
Noise and
interference on the voltage reference causes
amplitude modulation, and jitter on the clock causes
You're close. See the extra hint in a previous post.