mobile (cell) phone jamming

[Tarapia Tapioco]

I want to build a mobile phone jammer

* short range (not more than 5 yds)
* handheld, small
* battery powered

so that when I'm on the bus/train and some idiot start loudly talking
about his business, I can press a button and cause just enough
interference to disconnect him mysteriously.

It would be better if it had some directionality but not too much. I
don't want to aim it at someone but it would be nice to be able to
disconnect the loud phone user in front of me without affecting the
text messager behind me.

Can anyone point me in the right direction for designing this?

 

[Bob Stephens]

What's the problem? If someone annoys me too much with a phone, I just
offer to jam it somewhere. Manually. ;-)

When someone annoys me by yakking on a cell phone in a restaurant, meeting
etc., I just join right in the conversation "Sure thing Bill. Friday's
great. Just don't bring that whiny annoying wife of yours..." etc.
I get some priceless looks.

Bob

 

[Keith R. Williams]

Hey that's pretty good - worth a try.

Now, what is your technique for getting the woman on the road in the
SUV who is ambivalent about which lane she intends to use?

Bigger SUV with snow blade on front.

 

[Harry Conover]

I want to build a mobile phone jammer

* short range (not more than 5 yds)
* handheld, small
* battery powered

so that when I'm on the bus/train and some idiot start loudly talking
about his business, I can press a button and cause just enough
interference to disconnect him mysteriously.

It would be better if it had some directionality but not too much. I
don't want to aim it at someone but it would be nice to be able to
disconnect the loud phone user in front of me without affecting the
text messager behind me.

Can anyone point me in the right direction for designing this?

I'll assume that you realize doing something like this is a
non-trivial violation of federal law. Last time I checked, malicous
interferrence with federally licensed communications could earn one a
$10,000 fine, 10-years in prison, or both.

Cell phone jamming now already takes place in numerous facilities like
hospitals, theatres, restaurants, and other venues (quite thankfully),
but there it's confined to private property. Even then, it will likely
be shown by the ACLU or some other leftist group to be an encroachment
on existing communications law.

Harry C.

 

[Jim Thompson]

On 20 Dec 2003 16:40:40 -0800, [email protected] (Harry Conover) wrote:

[snip]

Cell phone jamming now already takes place in numerous facilities like
hospitals, theatres, restaurants, and other venues (quite thankfully),
but there it's confined to private property. Even then, it will likely
be shown by the ACLU or some other leftist group to be an encroachment
on existing communications law.

Harry C.

I think there's already been a court determination that *jamming*,
even on private property is illegal; but Faraday screening is legal.

...Jim Thompson

 

[Keith R. Williams]

Well that wouldn't work for long . . .

You have no clue how well it works. Mommy in the SUV will never
have a blade. Mommy in the SUV is petrified of anything larger
than she. A blade trumps a thousand pounds!

The whole idea of SUV's seems to be the "i'm bigger and badder don't
mess with me," syndrome. Whimps with a need to assert themselves?
Hogwash.

Doubtless that will draw a firestorm - but rationalize all you want -
you know, deep down, I'm right about this . . .

No, I know you're an idiot and a slimy leftist-pinko-drugged-up
freak! SUVs have this little 'U' in the middle.

So soon we are all trucking around in 6 ton, gas guzzling SUV's with
snow plows - what prevents someone with a snow plow from getting a
cell phone?

6-ton? Me thinks you gotta get your head out of the poppy field
here son! You are really whacked!

 

[Keith R. Williams]

I think you're response just proved my point.

You're an idiot. ...any relationship to DimBulb? ...like his
sister, or sock-puppet? You're *that* close.

Damn pissed off another SUV owner . . .

Get your head out of the bong. 6-tons? You are an idiot! (a
12000lb SUV, man you gotta get with reality!) Drop your penis-
envy and get with reality!

....and no, I don't own an SUV of any kind. I do own a small 4WD
pickup. We've already had 5' of snow this year. 4WD has been
very useful!

Why not just get some Viagra,
old man, and a more sensible vehicle? You'd save money and probably
have more fun. Assuming you can remember what fun is.

Suck some more Ganja. You'll have loads of fun rotting your
brain further.

 

[Bob Stephens]

Hey that's pretty good - worth a try.

Now, what is your technique for getting the woman on the road in the
SUV who is ambivalent about which lane she intends to use?

Well I live and drive in Los Angeles.... I could probably handle lane
ambivalence. It would be a step in the right direction for the SUV set out
here. What we have approximates Brownian motion!

-Bob

 

[John Woodgate]

I read in sci.electronics.design that default <R75/[email protected]>

I own a half-bottle of
aspirin - that's two years past its expiration date, does that count?

Much of it will have decomposed. Open the bottle and sniff. If it smells
strongly of vinegar, throw them away.

 

[John Woodgate]

I read in sci.electronics.design that default <R75/[email protected]>

Are you a chemist or pharmacist? Is it dangerous?

I studied chemistry for some years. Perhaps not dangerous, but
unpleasant to take because it's a lot more acidic, and aspirin is so
cheap that there seems no point in using outdated stuff.

 

[Tarapia Tapioco]

Why would it? The applications are totally different.

I agree. 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.

 

[Steve Terry]

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.

You're making it up at you go along !

No, how you jam a GSM phone is use a UHF mixer oscillator with a 45MHz
Oscillator which is the difference between the RX and TX of a GSM phone,
and put in a delay line so that the output of the jammer is in phase with
the phones input, causing feedback that stops the phone working.

Allegedly similar mixer osc devices (without the need of a delay line)
have been used to jam amateur radio, police, and PMR repeaters.
So I've been told

Steve Terry

 

[Ken Taylor]

You're making it up at you go along !

No, how you jam a GSM phone is use a UHF mixer oscillator with a 45MHz
Oscillator which is the difference between the RX and TX of a GSM phone,
and put in a delay line so that the output of the jammer is in phase with
the phones input, causing feedback that stops the phone working.

Allegedly similar mixer osc devices (without the need of a delay line)
have been used to jam amateur radio, police, and PMR repeaters.
So I've been told

Steve Terry

You'll have to run that one by me again - now I think *you're* making it up
as you go!

Ken

 

[Steve Terry]

You'll have to run that one by me again - now I think *you're* making it up
as you go!
Ken

A GSM phone receives on around 950MHz and transmits 45MHz down on
around 905MHz with a difference in multiplexed time slots,
so if you can make a little receiver that takes the 905MHz signal from the phone
and mixes it with a 45MHz osc putting a signal back out into the phones
receiver,
and time delayed so it interferes with the same time slots in the phones
receiver
you'll get a howl round, or you won't, as the phone would lose the network
trying to do so

Steve Terry

 

[Gordon Brown]

A GSM phone receives on around 950MHz and transmits 45MHz down on
around 905MHz with a difference in multiplexed time slots,
so if you can make a little receiver that takes the 905MHz signal from the phone
and mixes it with a 45MHz osc putting a signal back out into the phones
receiver,
and time delayed so it interferes with the same time slots in the phones
receiver
you'll get a howl round, or you won't, as the phone would lose the network
trying to do so

So how does the system know which frequency channel the mobile is on (there
could be several mobiles operating on several different channels
simultaneously) and how does this system cope with frequency hopping?

 

[Steve Terry]

So how does the system know which frequency channel the mobile is on (there
could be several mobiles operating on several different channels
simultaneously) and how does this system cope with frequency hopping?

You mix 45MHz with the phones own TX signal, from any phone nearby.
Then retransmitting itself up 45MHz into the phones receiver.

Whatever channel the phone is on, it's always a precise 45MHz diference

Without the phones transmit signal all the jammer puts out is it's 45MHz osc

What so difficult to understand ??

The difficult bit is adding the time delay so the phones TX time slots overlap
it's own RX time slots, otherwise the phone simply won't hear itself,
feedback, and stop working.

Steve Terry

 

[Ken Taylor]

You mix 45MHz with the phones own TX signal, from any phone nearby.
Then retransmitting itself up 45MHz into the phones receiver.

Whatever channel the phone is on, it's always a precise 45MHz diference

Without the phones transmit signal all the jammer puts out is it's 45MHz osc

What so difficult to understand ??

The difficult bit is adding the time delay so the phones TX time slots overlap
it's own RX time slots, otherwise the phone simply won't hear itself,
feedback, and stop working.

Steve Terry

But they randomize time-slots within the TDMA. For just one problem with
this technique.

Ken

 

[Gordon Brown]

You mix 45MHz with the phones own TX signal, from any phone nearby.
Then retransmitting itself up 45MHz into the phones receiver.

Whatever channel the phone is on, it's always a precise 45MHz diference

Without the phones transmit signal all the jammer puts out is it's 45MHz osc

What so difficult to understand ??

The difficult bit is adding the time delay so the phones TX time slots overlap
it's own RX time slots, otherwise the phone simply won't hear itself,
feedback, and stop working.

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?

 

[George Orwell]

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?

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?

 

[Ken Taylor]

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?

Probably not. Particularly a CDMA system, unless you put out so much power
that you were obvious to the crowd - the car battery, being up against a
wall, being cavity probed by the FBI........

Ken