On Dec 24, 2007, at 6:48 PM, Sean Breheny wrote:

> So, I've directly grounded the DVD player to the outlet and all is
> well now. I did some googling for this model of DVD player and didn't
> find anything about RFI problems. I suppose that what was happening
> was that the fact that the DVD player case was floating with respect
> to AC ground (and probably internally generating switching power
> supply noise), allowed the coax shield to become an antenna which
> somehow also coupled into the AC power lines.
>
> Anyone seen something like this before?


Not that particular product, but have seen it plenty of times in  
various "consumer" electronics.  Had a Linksys router throwing stuff  
all over VHF and UHF earlier this year (it seemed to have some sort of  
internal failure because it wasn't doing that the first three years I  
owned it).  The RFI was coming out all of the Ethernet ports.  It got  
thrown out so no one else would use it and pollute the spectrum.

There have also been a number of reports from various ham radio  
operators that certain Plasma TV's and LCD TV's (everyone buying new  
HDTV's in the States for holiday presents) throw some really nasty  
crap into the HF bands.

And don't even get me started about compact fluorescent lighting...  
the thought that there's actually idiots wanting to ban incandescent  
lighting in favor of these RFI emitters is rather telling in how  
little knowledge is left out there in the engineering world about  
RFI.  They're nothing but RF noisemakers.  Efficient yes, smart  
engineering to require them by law?  Not a chance.

(Not to mention that I still went ahead and tried a couple of brands,  
and all burnt out in similar timeframes to incandescent bulbs, which  
they're not supposed to do.  One even went up in smoke, while I just  
happened to be in the room.  I won't use them after seeing that.)

Consumer electronics in the U.S. are supposed to both accept any RF  
interference they receive and not generate any under Part 15, but it  
seems the standards for testing are lacking something... stuff goes  
out with high speed CPU's and virtually no shielding these days, and  
lots of products just spew crap, all over the spectrum.  It's getting  
harder and harder to find sources and mitigate them -- it's like the   
death of a thousand pinpricks.  And try going to your next door  
neighbor and tell him that his brand new $1000 HDTV is radiating RF  
into spectrum he's not licensed to operate on, and that he'll have to  
turn it off and contact the manufacturer, and see how far you get.   
Sure.  That's going to work.

I wish there were some good data taken of typical RF noise floor  
values in the 60's and 70's vs. today.  Anecdotally the noise floor at  
one of our radio sites that overlooks Denver @ 11,440' MSL has easily  
gone up 3 or more dB on VHF since the 60's... but I can't provide any  
hard data -- just going off of reports of performance of receivers up  
there over the years and having measured the noise floor this year up  
there.

--
Nate Duehr (WY0X)
nate@natetech.com
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