Hunt for RFI offenders

[esldude]

I have done the same thing at different frequencies with multi-band radios.  I've kicked around the idea of getting one of those inexpensive software defined radios.  The advantage would be you listen (via radio waves) once and can let software examine the bands of interest.  No need to tune a single frequency and check then do it all over again at another frequency. 

 

I never did that for the reason stated above.  I could tune in some nasty sounding noise next to gear.  A nearby in frequency radio station might drown it out.  In the worst cases the gear might overpower radio broadcasts, but 18 inches from the gear radio transmissions were able to dominate.  So the emissions from gear, if not in cabinets close to other sensitive gear (like a tubed MC phono stage next to a Mac Mini) just don't amount to enough to do anything. 

 

Also gave lie to the idea various tweaks in OS software could tune such systems for less emissions and better sound quality.  The same exact OS on various PC devices had dramatically different signatures.  And different OS on the same device had dramatically different emission signatures.  The whole thing in that direction is a fool's errand. 

 

 

[esldude]

2 hours ago, Ralf11 said:

Has anyone ever done listening tests by injecting noise into a device at different levels?

I have.  I posted files of music with noise added at different levels asking people to listen at their normal level and say when it disappeared.  Almost everyone heard it until -70 to -75 db and couldn't hear it below that. 

[esldude]

17 minutes ago, Ralf11 said:

 

Thx - this was injected via the regular inputs?

 

not via RF thru the case to the circuits...??

I actually simply added it to otherwise clean musical files.  So it isn't a test of how much RF can get thru devices.  Just a test of how much noise would have to result in it being heard. 

 

I have done things like wrap XLR cables around a high power switching PC supply.  Nothing came thru.  With RCA connection some noise did result at a mildly audible level.  Moving the RCA lines away 18 inches was enough to drop it below -130 dbv levels.  

[esldude]

7 hours ago, marce said:

As said it is a relevant paper but something simpler on BER or similar would be more illustrative of the point, someone did put up some figures and to be honest its a non issue these days in most instances...

They would moan if we still controlled stuff using 4-20ma loops etc. LOL but then maybe it was better because is was analogue....

 

4-20ma was a smoother more human control.  One where noise manifested itself as merely noise.