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Sherlock Ohms

Corrupt Data Filled the Air Waves

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Jon Titus
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More RFI Noise Sources
Jon Titus   7/10/2012 11:40:54 AM
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Amateur-radio operators routinely find RF-emitting sources that splatter noise across various frequency bands. Often street-lights circuits and malfunctioning power transformers cause the problems.  One of the oddest sources: a cordless-phone charger that produced intermittent noise that affected a local repeater in Massachusetts.  Members of the local ham club located the source and fixed the problem as described in this newsletter from 2005: http://www.mmra.org/newsltrs/mmnews_200501.lowres.pdf.  I belonged to the club at the time.

Rob Spiegel
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Re: Computer interference
Rob Spiegel   7/10/2012 1:16:27 PM
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Thanks for the info, Jim. So it's the carrier and not the phone. So it could be that an iPhone with a carrier other than AT&T wouldn't produce the interference. Does that make sense?

Jim_E
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Re: Computer interference
Jim_E   7/10/2012 1:19:48 PM
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Rob,

   Correct, it seems to be the carrier frequency utilized by AT&T, not the specific phone.  Some of my co-workers have Sprint iPhone 4S phones which do not generate the sounds, but the one with the AT&T iPhone 4 will generate the sounds.  And since we have poor AT&T service in our building, it makes the sounds a lot, since it seems to be constantly searching for better service.

Jim_E

Thinking_J
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Platinum
FCC class 15 .. interference issues
Thinking_J   7/10/2012 5:53:28 PM
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Way back in 1979... legal limits were put in place for unintentional radio interference from digital devices (by the FCC).

But many PC manufacturers were not testing for compliance. As the industry grew up, their liabilities became known and were better addressed.

As to Verison vs ATT for Iphone.. they have very different radios. GSM vs CDMA.
GSM is more likely to interact with your car radio..(ATT).. but it shouldn't interact much, unless there is something wrong with the phone or radios in question.

GSM will degrade in quality with interference and at the limits of it's range. Basically, it will sound bad before it drops out.

CDMA will hold higher quality ... but it's range (effective range) will be reduced as the cell tower: a) increases in traffic or b) sees an increase in interference. Basically, it wil sound great .. until it drops out entirely.

Often see CDMA radios that work at a given location (fixed) nearly all day but drop out entirely during "rush hour" from a near by freeway (as everyone is using their phones).. .Reason (simplistic version) : the fixed location was near limit of the tower range. The processing gain possible with CDMA is reduced as the channel traffic increases.

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