[RFI] Noise - where do I start?

[Cortland Richmond]

On 9/25/2016 1:31 PM, JW via RFI wrote:
> Can you put the Spec An into Zero span mode and use Line Trigger?

Back in the days of the open air EMC test site, when numerous ambient TV 
and radio signals had to be worked around, it was quite common to sync 
the spectrum analyzer to the line frequency and see the 
59.94Hz-modulated NTSC color signals crawling along on the screen.

It's sometimes helpful to look directly at interfering emissions in the 
time domain. When I'm using an employer's  shielded chamber, I can 
cascade preamps connected to an antenna and use [my employers] 6 GHz 
oscilloscope to examine the RF waveform directly.  If you ever have to 
sniff around for a *particular* SMPS, knowing what the waveform looks 
like means you can use a scope with a loop antenna on it to pinpoint the 
source.

Outside of a shielded room receiver  IF outputs can be used if a 'scope 
has the frequency response, or amplified a little and detected  detector 
to feed an AF scope.  This can be quite a bit more fuss to walk around 
with than a VR-500 or another handheld receiver, but I've used an ICOM 
ICR-7000 and an AOR AR5000- powered from 7AH AGM batteries; these days 
I'd use one of the high AH lithium packs sold as emergency starting 
batteries.

Handheld and battery-operated scopes are also available now that weren't 
in years past, but really, this elaborate a setup should probably be run 
from a platform on the front passenger seat and powered from the car's 
electrical system.  The advantage to walking around with something 
really portable is that you don't have to keep your eyes on the road.  
One trick: Turn off the AGC on the receiver to use a true RMS meter 
across a speaker, headphones or auxiliary audio output resistive load.

This impresses the audience more if you've calibrated the setup against 
a known-accurate signal generator.


Cortland
KA5S