Home |
Search |
Today's Posts |
|
#1
|
|||
|
|||
CB Radios, Cellphones and Gasoline Vapor Ignition
Claims that people have started fires by using
their cell phone while refueling a car apparently are false: See http://www.snopes.com/autos/hazards/gasvapor.asp and other sites. However, the first radios transmitted sparks, so in principle it should be possible to transmit near a long wire separated by a small gap from ground or another wire and get a small spark. So, I decided to try an experiment. I don't use a cell phone, so I assumed a CB radio transceiver would be a reasonable substitute: The power output of a nominal 5 W CB also is consistent and nonadaptive, so a possible unknown (actual output power) is avoided. Cell phones are adaptive and not very consistent in power output, so power should be monitored during a cell phone experiment. 5 W is considerably more than the 0.2 to 2 W typically possible from a cell phone; the power should be the important factor, although maybe someone should repeat this experiment with a cell phone, which would operate at a much higher frequency. I used a Radio Shack TRC-231 handheld (stock #21-1675) with xmit power on high and set on Channel 40. The antenna was the one that came with it (about 25 cm long). I set the volume to max and the squelch at min to be able to detect anyone else trying to use the channel; this was just to be sure that my brief, silent transmissions would not interfere with anyone. I used the CB indoors, in a mostly metal-shielded room. Because CB wavelength is around 10 m, everything I did was in the near field; however, the inverse square law for power still holds, allowing that the CB antenna is more of a line than a point source under my conditions below. The first thing I noticed was that every time I keyed the transmit button, the CB would switch the light level of a nearby touch-dimmed lamp, and it made a Microalert microwave detector scream. I unplugged the lamp and turned off the Microalert. Then, I tried to light a 120VAC indicator neon lamp attached to two solid copper switchback wires totalling about 1 m long, so the lamp was in the middle effectively of a dipole antenna. I tested the lamp and found it would light with 10 microamps current. The CB had no effect, even if held parallel to, and almost touching, the wires. Thus, the near field of a 5 W CB radio can not supply about 90 V at even 10 uA, under these conditions. I then attached a 1.2 m monopole antenna to an oscilloscope. This antenna has a Schottky hot carrier diode and impedance matching resistors builtin. It's home made, but it's probably as good as any other wire about that long. I hooked the antenna coax to an oscilloscope: With the CB transmitting, and its antenna parallel and 1 m away from the monopole, the amplitude was about 100 mV p-p, at 27 MHz or so. I could not get more amplitude no matter how close I held the CB, or at what angle. Touching the bare monopole wire increased the amplitude by no more than 10%. So, first conclusion: To get even a 1 V spark would take a wire at least 9 m long, all somehow kept within 1 m of the transmitter. Thus, it appears it is not feasible to create a hazardous spark with a CB at a gas station. Just to be sure, I taped a 1 m wire to a table top in the dark and slowly brought it closer and closer to another wire plugged into a wall socket 3rd wire ground (yes, I verified that the socket was wired to ground first!). At each distance, I briefly keyed the CB. I could not see any spark, even after dark-adapting my eyes for 10 min and letting the wires touch. I might have dark-adapted longer, but I don't know whether I should have been able to see a 50 mV spark or not. So, I think sliding over on a car seat, and thus generating a possible static charge, would be more likely to ignite gasoline vapor than talking on a cell phone while refueling. However, it would be useful for someone to repeat this kind of test with an actual cell phone, as opposed to a CB radio. The wires should be shorter, for one thing . . .. I'm cross posting to an antenna group, looking for criticism. John John Michael Williams |
#2
|
|||
|
|||
I was struck by a thought when I heard the latest Palestinian
terrorist trick is to send a kid through the border with a back-pack bomb triggered by a cell phone.... The Israelis should get a telemarketer's speed dialer and constantly dial away... boom... boom... boom... ROTFLMAO! ...Jim Thompson -- | James E.Thompson, P.E. | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona Voice480)460-2350 | | | E-mail Address at Website Fax480)460-2142 | Brass Rat | | http://www.analog-innovations.com | 1962 | John "Peace for our Time" Kerry, Neville Chamberlain of this Century |
#3
|
|||
|
|||
Jim Thompson wrote:
I was struck by a thought when I heard the latest Palestinian terrorist trick is to send a kid through the border with a back-pack bomb triggered by a cell phone.... The Israelis should get a telemarketer's speed dialer and constantly dial away... boom... boom... boom... If they could figure out from whom they're buying all them pre-paid cellphones (in order to generate the number lists), it could work. Just keep it running 24/7 with a "Sorry, wrong number" message in case an innocent (or unfinished bomb) answers. I figure eventually they'll run out of suicide-bomb volunteers. Might as well help if it can be done without blowing anyone else up. Mark L. Fergerson |
#4
|
|||
|
|||
On Wed, 17 Mar 2004 16:35:02 -0700, Mark Fergerson wrote:
Jim Thompson wrote: I was struck by a thought when I heard the latest Palestinian terrorist trick is to send a kid through the border with a back-pack bomb triggered by a cell phone.... The Israelis should get a telemarketer's speed dialer and constantly dial away... boom... boom... boom... If they could figure out from whom they're buying all them pre-paid cellphones (in order to generate the number lists), it could work. Just keep it running 24/7 with a "Sorry, wrong number" message in case an innocent (or unfinished bomb) answers. I figure eventually they'll run out of suicide-bomb volunteers. Might as well help if it can be done without blowing anyone else up. Mark L. Fergerson Do you all think that tangos are dumb enough to trigger the bomb with the ringer or would the detonator answer first and listen for a DTMF sequence. Hmmm? Achmed the bomb maker gets a wrong number just as he's connecting the thing. -- Best Regards, Mike |
#5
|
|||
|
|||
Active8 wrote:
[bombs] Do you all think that tangos are dumb enough to trigger the bomb with the ringer or would the detonator answer first and listen for a DTMF sequence. Hmmm? Achmed the bomb maker gets a wrong number just as he's connecting the thing. I very much doubt they bother with DTMF decoders. I mean, how often do you get a wrong number? I've had about 4 in my life. They'll just connect the ringer (or vibrate function) to the detonator (with whatever minimal circuitry in between is required - I've never used a detonator!) and then only turn the phone on at the last minute. It's not dumb to design a remote detonation system that requires the absolute minimum of specialist knowledge and equipment to construct. Tim -- Love is a travelator. |
#6
|
|||
|
|||
On Thu, 18 Mar 2004 05:39:21 +0000, Tim Auton
tim.auton@uton.[groupSexWithoutTheY] wrote: Do you all think that tangos are dumb enough to trigger the bomb with the ringer or would the detonator answer first and listen for a DTMF sequence. Hmmm? Achmed the bomb maker gets a wrong number just as he's connecting the thing. I very much doubt they bother with DTMF decoders. I mean, how often do you get a wrong number? I've had about 4 in my life. They'll just connect the ringer (or vibrate function) to the detonator (with whatever minimal circuitry in between is required - I've never used a detonator!) and then only turn the phone on at the last minute. It's not dumb to design a remote detonation system that requires the absolute minimum of specialist knowledge and equipment to construct. To use the unique cellphone ID to detonate a remote bomb is actually a very ingenious innovation. No timers to mess with. The terrorist has full and instant control of the time and place to set off the bomb. As Tim says its relatively easy to connect the ringer wires to a simple circuit to output enough juice to trigger the detonator. Frist year student project - like using a battery to keep a capacitor charged and the ringer closes the discharge switch. Boom. The countermeasure I think, is fairly simple. Every vulnerable public place which may be targeted by terrorist bomb attacks, should install cellphone signal blockers. I believe these are already available and smart dining places and concert halls have them so that their patrons won't be interrupted by cellphones. I'll skip the arguments, mostly from cellphone service providers, against signal blockers that may cause doctors and emergency workers to miss their calls. Until some better solution comes along I think this is a good solution. (Hint. Buy shares in signal blocker companies.) If this suggestion is taken up perhaps we'll get some peace from those incurable cellphone yakkers who think the world wants to hear every word they say anywhere. |
#7
|
|||
|
|||
On Thu, 18 Mar 2004 05:39:21 +0000, Tim Auton
tim.auton@uton.[groupSexWithoutTheY] wrote: Active8 wrote: [bombs] Do you all think that tangos are dumb enough to trigger the bomb with the ringer or would the detonator answer first and listen for a DTMF sequence. Hmmm? Achmed the bomb maker gets a wrong number just as he's connecting the thing. I very much doubt they bother with DTMF decoders. I mean, how often do you get a wrong number? I've had about 4 in my life. They'll just connect the ringer (or vibrate function) to the detonator (with whatever minimal circuitry in between is required - I've never used a detonator!) and then only turn the phone on at the last minute. It's not dumb to design a remote detonation system that requires the absolute minimum of specialist knowledge and equipment to construct. Tim New anti-terrorist weapon = telemarketers. They call everybody. Should wipe out the bomb makers in about a week. Dave Head |
#8
|
|||
|
|||
On Wed, 17 Mar 2004 13:08:33 -0700, Jim Thompson
wrote: I was struck by a thought when I heard the latest Palestinian terrorist trick is to send a kid through the border with a back-pack bomb triggered by a cell phone.... The Israelis should get a telemarketer's speed dialer and constantly dial away... boom... boom... boom... ROTFLMAO! Yes, I'm rolling on the floor laughing at all these deaths, too, as I'm sure we all are. -- The BBC: Licensed at public expense to spread lies. |
#9
|
|||
|
|||
"Paul Burridge" wrote : Jim Thompson wrote: : : I was struck by a thought when I heard the latest Palestinian : terrorist trick is to send a kid through the border with a back-pack : bomb triggered by a cell phone.... : : The Israelis should get a telemarketer's speed dialer and constantly : dial away... boom... boom... boom... : : ROTFLMAO! : : Yes, I'm rolling on the floor laughing at all these deaths, too, as : I'm sure we all are. Huh? He seemed to be laughing at the lame Idea! I also thought it funny that anyone would try something which would almost totally wipe out the cellular phone service for the entire country... All to provide a SMALL measure of confidence that no one had a bomb attached to a phone. Like it would even work! WTH are you referring to? GAL! |
#10
|
|||
|
|||
On Thu, 18 Mar 2004 00:09:30 GMT, Roger Gt wrote:
"Paul Burridge" wrote : Jim Thompson wrote: : :I was struck by a thought when I heard the latest Palestinian :terrorist trick is to send a kid through the border with a back-pack :bomb triggered by a cell phone.... : :The Israelis should get a telemarketer's speed dialer and constantly :dial away... boom... boom... boom... : :ROTFLMAO! : : Yes, I'm rolling on the floor laughing at all these deaths, too, as : I'm sure we all are. Huh? He seemed to be laughing at the lame Idea! I also thought it funny that anyone would try something which would almost totally wipe out the cellular phone service for the entire country... does a 200 station phone room with auto-dialers all calling one state wipe out POTs? WTH are *you* talking about? All to provide a SMALL measure of confidence that no one had a bomb attached to a phone. Like it would even work! WTH are you referring to? GAL! -- Best Regards, Mike |
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|