[sdiy] 100 MHz EMI, what can it be?

[Magnus Danielson]

From: "jhaible" <jhaible at debitel.net>
Subject: Re: [sdiy] 100 MHz EMI, what can it be?
Date: Mon, 14 Apr 2003 12:40:42 +0200

> >107,0MHz or 107,7MHz FM , 500W
> >
> >directly in my neighbourhood.
> >
> >Do you see something like this with your local
> >FM stations?
> >
> 
> I have once traced some "oscillation" in an Emu filter
> for hours, until I noticed it came "from the air".
> Why?
> It was my first time to use LM318 opamps, so I didn't
> trust them. And the circuit was so clean that I saw
> a periodical signal where in other circuits this would
> have been below noise.

It is when doing hunts like that I strongly advice the use of a spectrum
analyser if you have one around (which I do). The benefit of the spectrum
analyser is that you have a MUCH better ability to handle low noise signals
and high dynamic relations. What may seem like a mysterious odd signal on the
scope may become clear on the spec.

It is unfortunate that good specs isn't commodity instruments like
oscilloscopes. Then, it is unfortunate that oscilloscopes isn't commodity
instruments like DVMs, so I guess things are relative. Come to think of it,
people really should have a network analyser which may do wonders in the right
hands.

What people seem to want today is a DVM, a logic analyser and an oscilloscope to
figure out what's wrong (the same people usually doesn't know how to properly
use an oscilloscope I might add) :P

Cheers,
Magnus - wants a highspeed TDR/sampling scope, network analyser/spec into many GHz, logic analyser...