Waves Converter

This is the place for any magazine-related discussions that don't fit in any of the column discussion boards below.
Ron H
Posts: 360
Joined: Tue Dec 18, 2001 1:01 am
Location: Boise, ID
Contact:

Re: Waves Converter

Post by Ron H » Fri Dec 06, 2002 6:53 am

Power is measured in dB. Frequency is measured in Hz. They are totally independent. You can't convert one to the other.<p>I'm curious who it is you want to jam. If you own a restaurant or a theater or something similar, I'll be sympathetic. Otherwise... if I knew that you were jamming phones in my neighborhood, I'll guarantee you would be getting a visit from your not-so-friendly FCC investigators.<p>Ron

Michael-love-electronics
Posts: 84
Joined: Tue Nov 26, 2002 1:01 am
Contact:

Re: Waves Converter

Post by Michael-love-electronics » Fri Dec 06, 2002 8:21 am

Thanks for explaining but,... I still want to know what is meant by "low power RF of +20dB".???
I want to make a transmitter circuit that transmit +20dB so what frequency can this transmitter transmit.<p>Hope to find the answer despite of anything.<p>Thanks again :D

greg123
Posts: 361
Joined: Sat Sep 07, 2002 1:01 am
Location: St. John's NFLD Canada
Contact:

Re: Waves Converter

Post by greg123 » Fri Dec 06, 2002 2:13 pm

The transmitter can technically transmit any frequency you want. The 20 dBm, as already stated, is the amount of power referenced to 1 milliWatt (0.001 W) That is the amount of power...the Decibal Scale is the log of a ratio...<p>To deviate for a second;<p>Power in dB==<p>dB=10log(P/Pref)
to 1 milliWatt
dBm=10log(100 mW/1 mW)
=10log(100)
=20 dBm<p>So no way to convert to Frequency.......<p>Yes...Since 100 mW = 0.1 W That is low power at what ever RF you need.<p>[ December 06, 2002: Message edited by: Greg ]</p>

User avatar
jollyrgr
Posts: 1289
Joined: Thu Jan 03, 2002 1:01 am
Location: Northern Illinois
Contact:

Re: Waves Converter

Post by jollyrgr » Fri Dec 06, 2002 6:28 pm

Let's try this a different way. The dB is the power at some frequency F. Look at it this way. You can have a RED, GREEN, or YELLOW light bulb. The POWER output of the light bulb could be 7 watts to 300 watts. To use the lightbulb example you could have a RED lightbulb (frequency) at 100 watts (power). The power expressed in dB is the amount of power over some "reference" value. Thus to use the light bulb example, the cell frequency would be the color of the lightbulb, the wattage of the light bulb would be the dB.<p>Now you asked how to convert cell phone frequencies into RF. Well a cell phone emits and receives RF or Radio Frequencies. Thus CELL PHONE FREQUENCIES ARE RF! For those that do not understand the workings of a cell phone, let me explain using something a bit more simpler, a cordless phone. The old "49 MHz" phones used two different bands, 46 MHz and 49 MHz. A band is a set of frequencies in a certain range. The base TRANSMITS on a frequency in the 46 MHz band. A receiver in the handset RECEIVES on this frequency. Thus the handset could hear the phone line. The handset also has a transmitter that TRANSMITS at 49 MHz; the base has a receiver that RECEIVES at 49 MHz. Thus you have two transmitters and two receivers. One of each at each end of the system. When you have two paths for information like this it is called "FULL DUPLEX".<p>The same thing happens with a cell phone; but it gets a bit more complex with a cell system. (I'm making this VERY simplified so don't flame me for omitting things.) A cell phone "listens" on one frequency and periodically transmits a signal to say "I'm here" to the cell towers on another. This is so phone calls can be routed to the correct tower for the mobile phone. Let's say I take my phone from Miami to Los Vegas. How does the system know where my phone is at? It starts by the phone listening on several different reserved frequencies or "home channels". Depending on how the phone is configured, it will TRY to look for a home system (cheaper rates). Barring that it will look for any provider's home frequency (if you have programmed the phone to allow roaming). Once the phone finds a "friendly" channel it transmits a signal giving its unique identification information to the cell tower of the service provider. The provider then locates the information on the phone and then routes all calls meant for that phone to it.<p>The phone is constantly receiving something and waiting for a call. Every so often it transmits a signal stating "I'm here" so that the system knows the phone is still turned on. When a call does come in for that phone the system transmits a signal on the "home" frequency telling the phone it has a call for it; it also tells the phone what frequency pair to use to receive the call. The actual call takes place on a different frequency pair than that used to simply monitor the system. Just like I said above, the cell phone uses two frequencies to make a "duplex" call. Now lets say something goes wrong and two phones accidentally transmit on the same frequency at the same time. The stronger of the two signals at the cell tower wins (FM capture) and that phone's "I'm here" is acknowledged by the tower. The phone that "missed out" tries again and hopefully the phone gets its message to the tower. Once the tower receives a signal it acknowledges the cell phone and all is good. If the phone does not receive a signal, it will keep trying until it is finally acknowledged.<p>Recall how I said "PAIR" above? There is a standard "pair" of frequencies that the tower and cell phones use. The spacing is always the same between the frequency the phone uses verses what the tower uses. For instance, if the phone transmits on 400 MHz, it will receive on 500 MHz. If the phone transmits on 425 MHz, it will receive at 525 MHz. This is frequency pairing is known as a split. In this case the split is 100 MHz. It is not a RF signal of 100 MHz but a frequency DIFFERENCE of 100 MHz between the two frequencies. (These are NOT actual cell phone frequencies but are only simplified examples.) Also recall how the phone must transmit a signal AND receive a signal to keep the call up. The received signal also carries updates to the phone telling it to change pairs as it travels from tower to tower or as pairs become noisy for some reason or another. Now a call comes in or is attempted to be placed. Let say the phone transmits on 425 MHz once it acknowledges a call or attempts to make a call. It will be receiving on 525 MHz to hear the cell tower. But what if there is a near by signal on 525 MHz? The cell phone will not be able to acknowledge the cell tower and the call gets dropped! So how can all of this cause a cell phone to be "dumped"? Well it is all quite simple.<p>1) It is known what frequencies the cell phone itself transmits on.
2) It is known that if a phone is transmitting on frequency X it will be receiving on frequency Y.
3) It is known that the difference between X and Y is 100 MHz in our example. Thus you get: Y = X + 100 MHz.
4) It is also know that if the phone can't here the tower, the call gets dropped. <p>To put it simple, we need to listen for the cell phone to transmit a signal. We then add the "split" frequency to the received signal and transmit this so that the cell phone receives the BOGUS transmitted signal instead of the cell tower signal. Call is dropped. If all of this takes place on the "home" channel, the phone never gets identified by the phone network, thus no calls.<p>
Thus the "jammer" is simply a device that takes in a received signal from the phone, adds the split frequency to the signal, boosts the new signal, and sends it out as a new signal. In theory this is quite simple. This TYPE of circuit is in just about ALL radio frequency receivers (except things like crystal radios, regen receivers, etc.). It is a VERY common circuit called a MIXER/OSCILLATOR.<p>
From what you are posting tells me this. You have found a "black box" that you want to duplicate to jam phones. Based on the specs you posted, I can assume this much: The box RECEIVES a signal at a frequency "X" that is generated by the cell phone. It converts this frequency by the standard cell split, then AMPLIFIES the new signal by +20 dB. It then transmits this new signal so that the cell phone receives the BOGUS signal instead of the intended signal. Thus a dropped call.<p>
Building a jammer at the frequencies used by cell phones is a challenging task. While you MAY be able to get away with making or buying one of these, I would not want to get caught with one. Should a cell tech be troubleshooting a "dead spot" caused by one of these, it is quite easy to track down. (Shows up very readily on a spectrum analyzer.) I'll assume that you are in the US. If caught here this device COULD be considered a TERRORIST device (disrupting cellular infrastructure). In any case it is ILLEGAL to jam cell phones in most developed countries with the only exception I know of being Japan. Canada thought about legalizing these in places like theaters, concert halls, or other places where cell phones are a problem. Can jammers be located? Yes. It is quite easy to find these. Even without a spectrum analyzer if you used a cell receiver and determined that you were receiving a signal OTHER than the correct one from the tower, out would come the Direction Finding (DF) gear. If located you may only have the jammer confiscated. On the other hand you may be fined, jailed, or both. <p>To qoute a well known President, "I feel your pain". If you have this problem in a theater, simply find the manager and have them take care of the problem. I have personally done this. During the first showing of "Attack of The Clones" some idiot left his phone on. He then took a call DURING THE MOVIE! He did not leave the theater, he stayed in his seat! I went to the manager. Even though it was a young high school kid, he knew what to do. The jerk was still on the phone when the manager and I came back! The manager told him to leave, he was throwing him out. The guy first refused. The kid then told him if he did not leave, the police would be called. The PHONE JERK left to cheers of the entire theater!<p>[ December 06, 2002: Message edited by: Jolly Roger ]</p>
No trees were harmed in the creation of this message. But billions of electrons, photons, and electromagnetic waves were terribly inconvenienced!

Michael-love-electronics
Posts: 84
Joined: Tue Nov 26, 2002 1:01 am
Contact:

Re: Waves Converter

Post by Michael-love-electronics » Sat Dec 07, 2002 9:17 pm

Thanks very much for this detailed explanation,.. I really appreciate that.
It seems now from what Jolly Roger has said that the frequency received by the cell phone must be first changed by the jammer by adding the split frequency & resend it back to the cell phone.OK
sorry for the following silly Question:
How can I make a transmitter circuit that emitts 20dB or any power I specify.?<p>Thank you all very very much........ :) <p>[ December 07, 2002: Message edited by: Michael Wahid ]<p>[ December 09, 2002: Message edited by: Michael Wahid ]</p>

Bernius1
Posts: 349
Joined: Sat Sep 21, 2002 1:01 am
Location: NY
Contact:

Re: Waves Converter

Post by Bernius1 » Mon Dec 09, 2002 1:53 pm

try A)reading necessary books, taking courses,
and building prototypes, or,
B) http://www.fcc.gov
also look in dictionary under "malicious intent"
Can't we end all posts with a comical quip?

Michael-love-electronics
Posts: 84
Joined: Tue Nov 26, 2002 1:01 am
Contact:

Re: Waves Converter

Post by Michael-love-electronics » Mon Dec 09, 2002 8:40 pm

Thanks no_vice for that information,.. You have said what I want to hear,....SO
From where can I get these books, courses & prototypes.???????
please send me links :)<p>[ December 10, 2002: Message edited by: Michael Wahid ]</p>

greg123
Posts: 361
Joined: Sat Sep 07, 2002 1:01 am
Location: St. John's NFLD Canada
Contact:

Re: Waves Converter

Post by greg123 » Wed Dec 11, 2002 11:23 am

Try searches on amazon.com. Better yet, but a copy of nuts and volts mag. and look in their selection of books. They have some RF stuff there.

Michael-love-electronics
Posts: 84
Joined: Tue Nov 26, 2002 1:01 am
Contact:

Re: Waves Converter

Post by Michael-love-electronics » Thu Dec 19, 2002 1:25 pm

Thanks for this help but some more deatils will be appreciated.

User avatar
haklesup
Posts: 3048
Joined: Thu Aug 01, 2002 1:01 am
Location: San Jose CA
Contact:

Re: Waves Converter

Post by haklesup » Thu Dec 19, 2002 6:49 pm

Michael<p>I suspect that the design of a transmitter of your specification on both the circuit synthesis(theoretical design) and the actual physical circuit design (nevermind the special considerations you need to take in laying out an RF circuit onto a PCB) are well beyond the scope of this or any forum. <p>As I recall, communications theory in College was the culmination of many years of math and physics courses (and might I say the most difficult of undergrad courses I took)and given in the junior and senior years (if you've never heard of a Forier or LaPlace transform and don't know the difference between the time domain and S-Space then don't bother buying the book). Physical circuit design is actually a seperate art consisting of selecting components and connecting them etc. This is also not easly picked up (but can be copied).<p>Before I go, let me clear up some of your confusion.<p>What you want is a Transmitter which consists of an Amplifier (output power stage) and a front end (an oscillator plus lots of circuits to create just the right signal). The front end is anybodys guess for your application, it still is not very clear. This is where you might recieve an incident signal, mix it with another signal, and then modulate it(using AM, FM, SSB or whatever signal type you require) onto a carrier wave of whatever frequency you desire.<p>The amplifier according to your specs should emit RF energy (an oscillating electromagnetic field of a specified frequency)with an amplitude of 20dBm (which can be measured directly in the AC volts mode of my DMM tektronics TX3 and many others). Yes, Decibels are poorly understood even by engineers (except those dinosaurs who used a slide rule) but it is a measure of power not frequency and it does not describe the shape of the signal. Actually it is the ratio of the power you measure as compared to a standard output (ask yourself "how dim is the bulb compared to that standard bulb")<p>My meter states that dBm is measured across a 600ohm load P=V^2/R. An antenna's impedance can also be measured in Ohms (except we call it Z not R and it is variable with frequency)and the output voltage from the transmitter can also be measured. Thus we can compute power in Watts which we compare to a standard power radiated when the output is 1.000V and put that ratio (of power, volts or Amps) on a logyrthmic scale. (10Log(P2/P1) or 20Log(V2/V1) or 20log(I2/I1))<p>We call it dB and if we are measuring gain. In this case the gain in dB is the ratio of the input voltage (at 1.0V) to the the amplifier output. If the output were 1.0V it would have a gain od 0dB and 10V would have a gain of 20dB.<p>In the case of my meter with the 600ohm load it took 7.75Vac for it to read 20dBm. I think that in the case of dBm it is the ratio of the output power of the amplifier (P2) at 1 meter to the power measured at 1 meter if the output were (P1)1.000V. (someone correct me if I am wrong about that)<p>loosly defined; RF (radio frequencies) energy is any oscillating electromagnetic signal with high enough frequency to leave a conductor (antenna) and radiate into free space (the air) but not so high that it becomes light (look up "electromagnetic spectrum" for more on that). The power of this energy (measured in dBm in this case) will determine how far it will travel before its field strength is below background noise. <p>Just buy the thing if you want it, it's a heck of a lot cheaper than a college education. have you tried your question at sci.electronics.design or alt.cellular.telephones or alt.hackers among others

User avatar
Chris Smith
Posts: 4325
Joined: Tue Dec 04, 2001 1:01 am
Location: Bieber Ca.

Re: Waves Converter

Post by Chris Smith » Thu Dec 19, 2002 7:44 pm

Wiping out others is easy, you go dirty, and use the blanket effect. No math, no school needed. <p>I use pulsed laser drivers into semi balanced antennas instead of the diode. <p>A little experimenting and tank like circuits, a terminating resistor, and presto, the FCC is on your door step in hours! <p>Also No body in the neighborhood gets to watch TV, listen to radio, etc., even if they use cable? <p>Guaranteed.

Michael-love-electronics
Posts: 84
Joined: Tue Nov 26, 2002 1:01 am
Contact:

Re: Waves Converter

Post by Michael-love-electronics » Tue Dec 24, 2002 4:50 am

Thanks for this advice but I'll make this jammer for churches to avoid disturbance happened by these cell phones.
So any help will be appreciated.
:D

Michael-love-electronics
Posts: 84
Joined: Tue Nov 26, 2002 1:01 am
Contact:

Re: Waves Converter

Post by Michael-love-electronics » Fri Jan 03, 2003 12:45 am

Hi,...
Any ideas for how can I make a circuit that makes an interferance between to signals one of them is received and the other is generated from this circuit.?
the reeceived signal can be(RF or MW)......?
Tnanks and
HAPPY NEW YEAR

User avatar
haklesup
Posts: 3048
Joined: Thu Aug 01, 2002 1:01 am
Location: San Jose CA
Contact:

Re: Waves Converter

Post by haklesup » Fri Jan 03, 2003 12:55 pm

Michael<p>I didn't mean to be so pessimistic in my last post but I do still favor a low-tech solution here. A roll of "No cell phone" stickers (like the no smoking symbol) strategically stuck in visible places, a few "please turn off cell phone" signs by the door, a verbal reminder during the announcements part of the service and a one time printed hand out explaining the policy and reasons should eventually work. Once everyone understands that it is impolite to leave your phone on in church, you will have voluntary compliance and there will be no risk of legal liability for your church if your "project" should malfunction and blank out the whole neighborhood.<p>Be aware that you may also be jamming essential phone calls to doctors, law enforcement and volunteer firemen which could endanger the lives of others unintentionally. This is why I advocate the voluntary compliance (low-tech) solution. (plus it's illegal)<p>If you really want to know what is involved in the design process, take a look at the Dec02 (#149) issue of Circuit Cellar (may still be in stores) at the "Vector-SOC" project. While this is different, it does have a RF generator, a receiver section and lots of digital signal processing. The article will give you a very good idea of the complete design process you will need to go through. You can also find a PDF on the www.cypress.com website in the application notes section under PSoC since this was a contest winner.<p>I looked around a little and so far have not seen anything very specific to your request yet. Nor have I seen anything describing the theory behind cell phone jamming yet. I suspect that since this is a marketable product, IP owners are still keeping it to themselves.<p>
You can find lots of good background in the app notes for RF Mini-Circuits www.minicircuits.com/application.html
Don't miss the dBm - Volts - Watts converter table. . I also like Maxim-IC www.maxim-ic.com/appnotes10.cfm/ac_pk/38 they have a bunch of cell phone specific app notes at this URL. Try emailing their apps engineer directly for suggestions<p>Explore the legalities of jamming here.
http://www.wirelessnewsfactor.com/perl/story/8116.html
http://www.wirelessnewsfactor.com/perl/story/9856.html
http://www.osopinion.com/perl/story/18479.html (passive blocking)
http://www.longdistanceconnection.com/art2.htm <p>From one article --- A spokeswoman for the FCC reiterated the law — “jamming cellular transmissions are not permitted” in the United States — and said, “I’m not aware of any exceptions to the rules.”<p>What country are you in? The laws vary. But it is illegal in most countries and restricted where it is allowed. Evidently you can sell and own it but you can’t use it. Look in “spy Shop” or “counter- Espionage” stores to buy the equipment. This URL has a small jammer with a 10m range for $390 and a larger one for $560. http://www.microelec.com/misc.htm <p>Happy new year
Chris

Michael-love-electronics
Posts: 84
Joined: Tue Nov 26, 2002 1:01 am
Contact:

Re: Waves Converter

Post by Michael-love-electronics » Fri Jan 17, 2003 3:00 am

Hi,...<p>As I said before, This jammer will be used in churches only to avoid disturbance happened by these cells phones, also a note will be written says:"All cell phones will not work in church".
So everyone will enter the church will know that his cell phone won't work.<p>That's why I think that's important.
THANKS

Post Reply

Who is online

Users browsing this forum: Google [Bot] and 33 guests