Locating a cellphone jammer...

I'm interested in how the jammer might work, but it may be possible to set your phone to the 'hidden' (engineering) menu and get the signal strength and distance-to-cell readings. Either of these may be a good indicator of the location of the device. Google to see if there are codes available for getting access to advanced functions on your phone.

Ken

i............

Just a thought: Windows on your carriage were different: Metal-evaporated film for "heat control" which is also a perfect RF blocker for GPS as well as GSM. Been on the Gatwich Express and seen exactly the same effect (first AM run: 0515)...no other humans on the carriage. Definetly the glass (which was a different color.)

Just a thought.....................

webpa

Are these trains underground? Also, could it be possible that the train has some sort of rf generating device, either via cable or via antenna that could be interfering? Usually trains communicate in some fashion. If they have a transmitter on board, if you were located close to the antenna and it was transmitting "trash" it could very well interfere with your phone. Brian.

Metal-evaporated

as

AM

was a

No - as I mentioned, as soon as we left the first station, everyones 'phone started working again. There was no "Faraday Cage" effect.

Mike

has

it

I take this train every day, twice a day - have done for years. First time this effect has been noticed. Its a standard (rather old & crappy) overground train in the SE of England - last carriage in train, furthest from the driver's cab..

Also, doesn't explain why as soon as we pulled out of the first station everyones 'phones started working again.

Mike

Did the train switch from overhead lines to a third rail at the first station? It could have been RFI generated by part of the train's power pickup mechanism.

Tim

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'phone

There is no over-head cabling on that line - its never happened before in years of using the line twice every working day - its all "third rail" power.

Mike

You may be able to roughly localise it by walking backwards and forwards to determine the center of the "dead zone" The jammer should be somewhere near there. You probably then need a FSM tuned to about

860 MHz, might get you some funny looks on the train however!

Or, perhaps something like an ICOM R1 with an earpiece, you should be able to hear the jamming signal, and then try to maximise the signal strength as you walk about.

Barry Lennox

Just report the incidence to the phone company technical services. It is possible at the frequencies that these phones work on, you can have isolated dead spots.

I am in a high-rise building, and the cell company has an antenna array on the roof. In this building the cell reception is so bad that the cell phones are almost unusable. This is because we are under the lobe of the antenna.

In the town where I live, there are a number of dead spots. I know where a few of them are. Infact, I know of one that is so acute, I can walk about

50 feet, and the phone is at near zero signal strength on its meter. The support tech at the phone company told me that they are aware of the problems, and it would be too expensive for them to fix just to cover a few thousand square feet where there is not very much cell phone traffic.

I have a feeling you ran in to something like this.

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Jerry Greenberg GLG Technologies GLG ========================================= WebPage

Electronics =========================================

If you thought that someone in the near vicinity had a cellphone jammer about their person, how could you simply locate it?

This is in Europe - GSM. These items are illegal for civilian use in the UK, and I suspect that someone was using one on the train tonight

- for 30 minutes, no-one's cell phone worked in our carriage until we got to a station, then, like a miracle, they all started working again. If I moved to the next carriage (about 30mtrs, my phone started to work again - the signal got better the further I moved from my original carriage. All networks were effected (O2, Vodaphone, Orange), so I suspect that it was a jammer being used with a radius of about

15mtrs or so and when the person got off the train at the station, everything worked. We must have travelled through many cells and network providers in the 30 minutes, so it certainly wasn't network downtime...

How could I identify who was using it? I hate the use of cell phones on trains - but this is more of academic interest...

Thanks

Mike

I am in no way experienced with propagation issues at cell phone frequencies, but wouldn't a spark gap in an appropriate cavity jam quite well?

...Jim Thompson

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|  James E.Thompson, P.E.                           |    mens     |
|  Analog Innovations, Inc.                         |     et      |
|  Analog/Mixed-Signal ASIC's and Discrete Systems  |    manus    |
|  Phoenix, Arizona            Voice:(480)460-2350  |             |
|  E-mail Address at Website     Fax:(480)460-2142  |  Brass Rat  |
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I love to cook with wine.      Sometimes I even put it in the food.

I think youre missing the point. Electronic transmitters get worse with age. The older they get, the "dirtier" the signal. It could be that the station you pulled out of has an old transmitter that is creating hash in your phone band. B.

they

and

What frequency bands do cell phones transmit in?

Most of the stuff I saw on my spectrum analyser was 900Mhz; very, very narrow-band signals almost like intermittent spikes.

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My opinion is worth what you've paid for it.

Well, when last I paid attention, US cell-phones did their thing in the

806-899 MHz range. That may have changed in the 8+ years since I paid attention to details that picky, however, and might be completely wrong for non-US cell systems.

Back in the days when UHF television channels hadn't yet been pruned to make room for other things, the top channel (was it 83, or 69? I'm having a brain-blank episode, and have no references handy) of the TV set could pull in *SOME* cell-phone signals. Generally, the quality was crap (Cell phones are operating with a different bandwidth than TV audio, so this is to be expected) but it WAS possible to listen in on cell-phone conversations that way. Not long after that was discovered by the general public, the top 20-ish channels of UHF ceased to be licensed for TV use, got re-dedicated to something else, and TV makers stopped making sets that could tune that range.

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Don Bruder -  dakidd@sonic.net

It depends on the network and the technology. It can be in the 800 or 1900 MHz range. Brian

From memory, for analog tansmissions it is in the 824.o4 to 893.70 mHz bands. For the digital network they are in the 1850 to 1990 mHz bands.

Jerry Greenberg

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"Reg Edwards"  wrote in message
news:...
> What frequency bands do cell phones transmit in?

US UHF used to go to Ch 83, now it stops at 69

Here is a link to my US TV channel reference chart:

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Take a look at this little cutie! ;-)
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Michael A. Terrell
Central Florida

Digital modes can use the lower (800MHz) band as well. Individual phones hunt around for a paging channel they like, and that channel tells them which other channels are usable for their particular mode.

GSM uses a 200-kHz wide channel and transmits in a 546-usec burst every

4.6 msec. Other systems have other channel spacings and frame rates.

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      Wim Lewis , Seattle, WA, USA. PGP keyID 27F772C1

From:

Mobile phone transmit Base station transmit Vodafone GSM 900: 890 - 894.6 MHz 935 - 939.6 MHz BT Cellnet GSM 900: 894.8 - 902 MHz 939.8 - 947 MHz Vodafone GSM 900: 902 - 910 MHz 947 - 955 MHz BT Cellnet GSM 900: 910 - 915 MHz 955 - 960 MHz Vodafone GSM 1800 & BT Cellnet GSM 1800: 1710 - 1721.5 MHz 1805 - 1816.5 MHz One2One GSM 1800: 1721.5 - 1751.5 MHz 1816.5 - 1846.5 MHz Orange GSM 1800: 1751.5 - 1781.5 MHz 1846.5 - 1876.5 MHz

Wim