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Thinking_J
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Platinum
FCC class 15 .. interference issues
Thinking_J   7/10/2012 5:53:28 PM
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.

Jim_E
User Rank
Platinum
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

Rob Spiegel
User Rank
Blogger
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?

Jon Titus
User Rank
Blogger
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.

dnason@kicmail.com
User Rank
Iron
Da..ed CB'ers
dnason@kicmail.com   7/10/2012 11:11:43 AM
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Years ago, my wife would call out to me that the TV was messing up. Living in a rural community, but during the height of CB popularity, we assumed it was a neighbor using their CB radio, possibly with an (illegal) power amplifier. This went on for weeks and we coined the phrase DCB for "Damn CBers". One night it hit me though - the only time she complained was when I turned on my new Osborne computer. Apparently there were enough harmonics coming from the blazing fast 4 mHz Z80 processor chip to interfere with the television rooms away. That solved the mystery of who the DCB was, it was me. In those days, I only occasionaly used the computer unlike today when it is hardly ever turned off and since I was constantly fiddling with something in my basement workshop, it took some time to make that connection.

Larry M
User Rank
Platinum
Re: IBM 1620 Computers Played Music Ages Ago
Larry M   7/10/2012 10:52:31 AM
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The previous few generations of ATM (cash) machines generated a fanfare at the conclusion of a transaction by cycling the receipt printer printhead back and forth at the appropriate rates and distances.

Larry M
User Rank
Platinum
Re: Computer interference
Larry M   7/10/2012 10:49:35 AM
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The GSM poll rate is 277 Hz, right in the audio spectrum. I live in a low-signal area, so my GSM cellphone is always transmittting near maximum power. It's tone can be heard on the laptop speakers and on my wireline phone if I don't place it carefully, and I am sure I could hear it on AM radio if I tried.

 

Jim_E
User Rank
Platinum
Re: Computer interference
Jim_E   7/10/2012 10:24:01 AM
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Rob,

   Yes, audio interference from AT&T GSM phones is very common if the phones are close to a speaker.  My wife's old RAZR flip phone does it ,as does my co-worker's iPhone 4.  As the other poster mentioned, it seems to happen when the phone is searching for towers.  My wife's phone will also generate the noise just before her phone rings.  Quite annoying.

   Since I switched to a Sprint phone, I haven't heard the sound once, so it seems to have something to do with the frequency that the AT&T GSM phones operate on.

Jim_E

tekochip
User Rank
Platinum
Re: IBM 1620 Computers Played Music Ages Ago
tekochip   7/10/2012 8:32:09 AM
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Back in the early days of computing we did some pretty crazy stuff to make music. Most small computers had cassette ports for saving programs and that was hacked into for music. There was another one for uploading code into a Commodore floppy's RAM so that the stepper mode could sing, but my favorite was using a dot matrix printer.
 
No knowledge is wasted, I still use the singing motor and sometimes solenoids in appliances as a beeper.


Jon Titus
User Rank
Blogger
IBM 1620 Computers Played Music Ages Ago
Jon Titus   7/9/2012 11:31:32 PM
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Back in the mid '60's I remember hearing Christmas carols "played" by an IBM 1620 computer via an AM radio. Someone said a program caused certain sequences of clock signals that radiated the "music" the radio picked up.

Tonight I found this: "From Bill Principe, 16 Sep 2005:

I saw your 1401 and 1620 pages on the Internet. As an undergrad at Berkeley in the 60s, I had part-time jobs working on both machines. I'd like to share a 1620 anecdote.

There used to be a program for the 1620 that worked line this. You put an AM radio on the CPU console, and tuned it for the loudest noise. (They generated a lot of random RF noise that could play havoc on nearby electronic equipment.) Then you fed a deck of cards with the program. The radio would play "Stars and Stripes Forever" and the line printer would play the drum rolls. I'd like to see a Pentium IV laptop do that!"

Here's the source: http://www.columbia.edu/cu/computinghistory/1620.html, so it seems as though programmers pretty well mastered creative uses of computer generated RFI some time ago.

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