On Mar 29, 2008, at 8:49 AM, Jack Smith wrote:
> GSM is particularly  bad for RFI because it has a 216 Hz frame rep  
> rate,
> which, when rectified, looks like a 216 Hz square wave. Old analog
> phones had a continuous carrier and CDMA phones have less of an EMC
> footprint as well.

Very interesting.  I always knew anecdotally that my GSM phones always  
were worse than my CDMA phones over time, but didn't know why.  I had  
an article stashed somewhere here on the hard drive to read about it,  
but never got around to it.  Your sharing here covers it well enough  
for my curiosity in a single paragraph.

While we're on the topic... anyone here have good recommendations for  
powered/amplified PC speakers that are RF noise-resistant?

To be frank, I think hooking the PC up to an old 70's stereo and  
similar era speakers would be better than the RF hash crud filled  
speakers I keep finding in the PC marketplace.  I have a very nice set  
of now very old Altec Lansing speakers and a subwoofer that sound  
GREAT hooked to the lightly used desktop PC down in the basement, but  
the ham rigs, cell phones, just about everything... drive them  
insane.  I keep thinking about opening them up and working on that,  
but I'm lazy... and have other more useful things to get done... I end  
up just powering them off when I get "RF active"...

There are some companies selling mono amplified speakers they claim  
are for "communications" (hint: This means they rolled off the high- 
end to reduce the fatigue of accurately reproduced white noise from a  
receiver) that also have great RF shielding in them, but they want an  
arm and a leg or two for them.

Any thoughts from the assembled masses here as to good ways to have  
decent levels and quality of sound from a PC that don't include  
listening to your cell phone check in with local tower every so often,  
or blowing you out of your chair whenever the phone receives an SMS or  
incoming call?  :-)

Extra brownie points for being able to stand up to 100W near fields  
for HF through VHF, 50W at UHF, and 900 MHz at 11W, or... maybe even  
1.2 GHz at 10W.... SSB, FM, AM, whatever...    :-)

--
Nate Duehr
nate@natetech.com



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