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mobile (cell) phone jamming

G

Gordon Brown

Jan 1, 1970
0
George Orwell said:
"Gordon Brown" <.> wrote:
That's what I was thinking. This would be a lot simpler than having to
detect a specific signal, modulate it by 45MHz an retransmit it.

Would the white noise across the right frequency band confuse the
phone enough to disconnnect or garble the call?

I am no RF engineer, but IIRC, building a broadband transmitter
intentionally is not that simple. Also the noise will have to be above the
signal from the base station transmitter (say 50W transmitter?). I wonder if
it would not be easier to jam the uplink signal as this would only require
the jammer to transmit in the same order of power as the mobile.
 
T

Thinker

Jan 1, 1970
0
Tarapia Tapioco said:
I agree. The car lock remote uses infrared (I think)

If this is about North America you are way out to lunch. All we have here
are
RF remote controls for cars.





and transmits a
 
S

Steve Terry

Jan 1, 1970
0
Gordon Brown said:
Ah, I see, you mean a broadband jammer (otherwise it will not cope with two
phones transmitting on different channels). For some reason I was assuming
that it was some elaborate narrow band jamming device. Why not just transmit
a burst of white noise at 950Mhz with a 45MHz BW?
Broadband yes, but not broadband jamming, it's providing from the phone TX
a mixed signal to go back into a phones RX, the more phones within it's range
it's trying to mix, the weaker the individual output signal from it.

Steve Terry
 
S

Steve Terry

Jan 1, 1970
0
Ken Taylor said:
Steve Terry said:
Gordon Brown said:
But they randomize time-slots within the TDMA. For just one problem with
this technique.
Ken
Doesn't have to be precise, just as so there's enough time slots interfered
with to stop the phone from working.

Steve Terry
 
S

Steve Terry

Jan 1, 1970
0
George Orwell said:
Gordon Brown said:
That's what I was thinking. This would be a lot simpler than having to
detect a specific signal, modulate it by 45MHz an retransmit it.
A broad UHF input 45MHz mixer osc with broad UHF output is very simple to make
Would the white noise across the right frequency band confuse the
phone enough to disconnnect or garble the call?
A broadband UHF white noise jammer would have to transmit very much more power
to have an effect

The whole point of the phone operating on a 45MHz split with odd phased
time slots is so the phones RX doesn't hear it's TX.
Upset any part of that cycle with a relatively low signal, and the phone stops
working.

Steve Terry
 
G

Gordon Brown

Jan 1, 1970
0
Steve Terry said:
The whole point of the phone operating on a 45MHz split with odd phased
time slots is so the phones RX doesn't hear it's TX.
Upset any part of that cycle with a relatively low signal, and the phone stops
working.

So what sort of delay would be necessary and to what tolerance?
 
S

Steve Terry

Jan 1, 1970
0
Gordon Brown said:
So what sort of delay would be necessary and to what tolerance?
A few microsecs ?
I would guess interfere with as little as 20% of the slots to stop the phone
working

If there is already a random element in the slots maybe just letting the
phones RX see it's TX with a nearby 45MHz mixer osc could be enough ?

Steve Terry
 
J

Jim Thompson

Jan 1, 1970
0
On Tue, 23 Dec 2003 20:10:37 +0100 (CET), Tarapia Tapioco

[snip]
.... The car lock remote uses infrared (I think) and transmits a
very specific signal that the car receiver detects.

The jammer would use cellphone frequencies (around 9GHz and similar
bands, I think) and would need to transmit--I think--white noise
across the target band, strong enough to drown out the signal the
phone is already receiving.

ROTFLMAO! Infrared ?:) 9GHz ?:)

The best defense we have against such folly is that the perps are
village idiots ;-)

...Jim Thompson
 
Z

Zak

Jan 1, 1970
0
Steve said:
If there is already a random element in the slots maybe just letting the
phones RX see it's TX with a nearby 45MHz mixer osc could be enough ?

Well, if you build a PLL it should not be too hard to keep it running
in the channel for the moments that the reference signal is off.


Thomas
 
S

Steve Terry

Jan 1, 1970
0
Zak said:
Well, if you build a PLL it should not be too hard to keep it running
in the channel for the moments that the reference signal is off.
Thomas
Shouldn't need the complexity, phones only just manage not RX their own TX
45MHz away under normal conditions

Steve Terry
 
G

Gordon Brown

Jan 1, 1970
0
Steve Terry said:
Shouldn't need the complexity, phones only just manage not RX their own TX
45MHz away under normal conditions

The GSM downlink and uplink bursts are spaced 3 burst periods apart, with
the downlink burst occurring first. This means that (in the case of
frequency hopping enabled) the GSM mobile will be receiving and transmitting
on Channel A before moving on immediately to a different channel from its
next reception and transmission. In this case, I doubt such a simple
"delayed-feedback-interferer" would actually jam a GSM mobile station in
practice under normal conditions .
 
G

George Orwell

Jan 1, 1970
0
Gordon Brown said:
I am no RF engineer, but IIRC, building a broadband transmitter
intentionally is not that simple. Also the noise will have to be above the
signal from the base station transmitter (say 50W transmitter?). I wonder if
it would not be easier to jam the uplink signal as this would only require
the jammer to transmit in the same order of power as the mobile.

This sounds promising for technical reasons (simplicity,
effectiveness, ease of use) BUT the jammer would have to produce as
much output power as the phone -- this would make it much easier for
"the authorities" to locate the jammer.

How much power at a short distance (I think the OP said a few yards)
would be required to overpower the cell's signal to the phone
(powerful but much more distant)?
 
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