cpitchford | # 21 | 2010-04-15, 17:46 | Report

You're suffering from "transistor at the end of a wire aerial"

Magnets (particularly stationary ones) will have no effect on a wire with no current.. when current passes through them, the wire will try to move in the magnetic field.. this is how motors work.. it is not going to cause a problem with a keyboard.

The "duh-d-d-duh-d-d-duh-d-d-duh" sound people may recall hearing from speakers when GSM phones were nearby is caused by poor filtering on the speakers.. interference is picked up by speaker wire/audio cable/whatever.. .Since GSM (and 3G) transmitters pulse on and off rapidly, this makes it harder to filter.. Here's an example:

a 100W FM transmitter next to a 1995 TV wouldn't necessarily cause any problems because the radio signal is of a constant strength.. However, turn the transmitter on, you get a snap of interference.. turn it back off, again another snap..

This is the same thing that causes clicks on the TV screen when your refrigerator motor turns on / off..

It is CHANGE that causes the problems like this.. and a GSM transmitter is constantly turning on and off..

Speakers (more accurately amplifiers) and TVs are immune to this NOW because the filters got better..


Your keyboard may not be sufficiently filtered for a) a pulsating radio source like the phone, or b) for a constant but high frequency transmission.. Either way, this is going to be rare and doesn't indicate a problem with anything other than your keyboard..

It won't have any affect on a human because we're not subject to interference, we're affected by absorbtion.. that's very different.

ChoMar | # 22 | 2010-04-15, 19:46 | Report

Thats strange. The shielding of the Ethernet Cable is very good and should work both ways...

The diagnostics may be difficult. The comparison with the FM - Trasmitter doesnt really work since we have to take Frequency in to account. The problems with speakers is also due to the Frequency, as far as i know.

Without any resonance the signal would be much to weak to interfer with the Keyboard (or Speakers) i think.

Is the Keyboard connected via PS2 or USB? Cause then some HW-Geek could find out the Frequency this Standarts work with and than we could do some simple math to check if the Frequency of the Mobile is a direct multiple. Are other Keyboard functions influenced?

mzanetti | # 23 | 2010-04-15, 20:02 | Report

I think it's PS2... Not 100% sure now as it's on my office PC and I'm at home. Will double check tomorrow and post if I'm wrong.

When I tried it on my collegues keyboard, he told me that the windows key has been triggered. However, I was behind his screen and couldn't see it myself.

I can confirm that at least the caps lock key has also been activated on my PC. So its not just the LEDs flashing. It does actually trigger keypresses.

Oh! And we have tried to reproduce the same using a Huawai USB GSM/UMTS Modem and the same service provider. It didn't work...

ChoMar | # 24 | 2010-04-15, 20:18 | Report

The Clock frequency of a PS/2 Keyboard is something between 10 and 17 kHz, if i remember correctly. What service provider do you use?
i dont know if we can work with the informations, then. but we could try to do some math, maybe we find a correlation.

Yeah, playing with high frequencies is an interesting field...youll never know what happens. GSM isnt THAT high (with WLan everything is possible, even transdimensional connections. But its also possible that a connection fails if the devices are 5m away from each other) but its high enough to be quite unpredictable.
Could be that you managed to place you device in the EXACT right angle or something else. Polarity is the thing to take into account here. And much other things.

mzanetti | # 25 | 2010-04-15, 21:08 | Report

E-Plus, germany. According to wikipedia it has 900 and 1800 MHz bands. Anyone knows the AT command for the N900 modem to check currently used band? AT+CPWC as stated in the docs for Nokia GSM modems doesn't seem to work.

Yes, position and angle seem to be important to reproduce this, but I'm able to be reproduce it anytime with this keyboard, so I don't think it needs to be an EXACT right angle

check out the video linked on page 2...

cpitchford | # 26 | 2010-04-16, 00:09 | Report

The example with the FM transmitter is quite relevant. It is not the frequency, it is the fact the transmitter in the phone is turning on and off rapidly.. the tone of the buzz on the speakers is not resonance, or anything to do with the broadcast frequency it is the tone of the transmitter being turned on and off..

this is why it is goes d-d-d-duuur... the longer sounds are longer periods of broadcast, the short clicks are usually idle periods when little data is being broadcast (ie you're being quiet)

It is far more likely to be a saturation issue.
10Khz versus 1900Mhz? That's like a bat trying to talk to a blue whale.. they won't be able to hear each other at all (190000 times more rapid!)

If sufficient voltage is induced in the cable, then it would might be sufficient to upset the primitive cpu in the keyboard.. The frequency probably doesn't have too much to do with this..


The IR receiver, btw, is because it is designed to pick up very quiet signals from the IR receiver.. any eletrical noise next to such a device an upset it.. I've seen that a few times..

Tizbad2k | # 27 | 2010-04-16, 00:14 | Report

Im an electrical engineer and I very recently attended an internal talk within my department about cellphone radiation and whether or not it is hazardous to health.

To sum it up:
1. There is absolutely no chance whatsoever of doing damage at cellphone frequencies. There is zero correlation between cancer and cellphone use. 60 hertz power lines are infinitely more dangerous than the high frequency used in GSM, power lines are considered a class 2 carcinogen.
2. Holding a cellphone to your head heats up your head not because of RF but because of the batteries inefficiency at energy conversion. Mildly increased cranial temperature actually leads to reduction of cancerous tumor size (if you happen to have a tumor).
3. Even having a cell phone tower near your house does not expose you to any serious radiation. Cellphone towers radiate outward and conically, Standing directly under a cellphone tower means you get almost zero incident radiation. You would have a hard time measuring the signal from a tower even with very sensitive equipment if you were directly under it.

There is ZERO risk associated with RF from cellphone. Dont worry about it.

juise- | # 28 | 2010-04-16, 09:07 | Report

Note that he said Cat5 (which is just four twisted-pair wires wrapped in plastic) instead of Cat5e (same as above, except the wires are wrapped in a tin foil).

Also, the ethernet cable shielding is mostly meant to prevent far-field effects (basically to prevent the cable to act as an effective antenna). It cannot do much for near-field effects (esp. inductive coupling).

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Last edited by juise-; 2010-04-16 at 09:09. Reason: syntax

shadowjk | # 29 | 2010-04-16, 20:47 | Report

There's both shielded and unshielded Cat5e and Cat5. FTP, STP, UTP...

Benson | # 30 | 2010-04-17, 02:52 | Report

Sorry, but it tells you wrong. The signal being received is the TDMA time-slot rate (something like 220Hz IIRC) in GSM. Given that your speakers are serving as a completely unintended (and thus unoptimized) AM receiver and demodulator, it's highly unlikely they receive 850MHz (much less 1900 MHz) and completely reject 1700MHz.

The simple, correct explanation? There's no corresponding audible AM signal in UMTS, since it's CDMA instead of TDMA. When a phone uses GSM (2G) you get buzz, when it uses UMTS (3G) you don't. If you ever find yourself missing the noise, set your N900 to 2G mode, and it'll be right back...


As to the OP's keyboard issue -- nothing to worry about, when you sit a transmitting antenna 5-10mm from an (unintended) receiving antenna, any powered electronic device has a decent chance of serving as an equally unintended receiver and doing something unexpected with that signal. It doesn't follow that you'll suffer interference when using them at more typical separations (inverse-square law), or that the RF is of sufficient intensity to cause any health problems (because your brain, genitalia, or whatever else you're worried about aren't powered-up amplifiers -- the worst that can happen is complete absorption, resulting in at most a couple watts of heating distributed over a large area).