2)From: "Brandon Robinson" <brobinson@navicom.com> Subject: Re: Monitoring MDT's
14)From: "self destruct" <<slfdstrct@email.msn.com> Subject: Monitoring MDT's hi all,....i am wondering if there is a way to monitor police MDT's (mobile display terminals) i have the frq. that they use but i dont know how to hook up a scanner to p/c. any thoughts would be appreciated thank you
Since no one else seemed to respond to this, I guess I will...first off M.D.T. stands for (Mobile Data Terminals), I got this posting off some group I can't really remeber where from, but it is informative, and was the subject of a Feb, '97 "911Dispatcher Magazine" story. It should answer all of your questions, I also have a list of some places where you can buy the unit pre-made, or a kit to make your own. I have left the Source code out on purpose as it is rather lengthy, if you want it I can send it to you. -BBR ----------------------- Begin quoted article ----------------------
From lord@heaven.com Mon Dec 23 23:11:43 EST 1996 Article: 44420 of alt.radio.scanner Subject: MDT stuff
Greetings one and all, Have you ever lusted to decode Mobile Data Terminal (MDT) tranmissions? Have you ever wanted to see the same NCIC and motor vehicle information that law enforcement officers see? Have you ever wanted to see what officers send to each other over "private" channels? And all this with an interface you can build with only a few dollars worth of parts from your local radio shack? If so this posting might be your rendevous with destiny. The tail end of this posting includes the source code of a program that decodes and displays MDT messages. It stores roughly 30k of messages in a buffer and then writes the whole buffer to a file called "data.dat" before terminating. The program may be interrupted at any time by pressing any key (don't use control-c) at which point it writes the partially filled buffer to "data.dat". This program only works for systems built by Motorola using the MDC4800 tranmission protocol. This accounts for a large fraction of public service MDT systems as well other private systems. The existence of this program is ample evidence that Motorola has misrepresented its MDT systems when it marketed them as a secure means of communcications. The interested reader will soon discover that these systems do not use any form of encryption. Security concerns instead have been dealt with by using a code. "And what might this code be called?" asks the reader. The code turns out to be plain ASCII. What follows is a brief description of how the program and the MDC4800 protocol work. If you don't understand something go to your local library and check out a telecommunications theory book. 1. The raw transmission rate is 4800 baud. The program's interrupt service routine simply keeps track of the time between transitions. If you're receiving a perfect signal this will be some multiple of 1/4800 seconds which would then give you how many bits were high or low. Since this is not the best of all possible worlds the program instead does the following: transitions are used to synchronize a bit clock. One only samples whenever this clock is in the middle of the bit to produce the raw data stream. This greatly reduces jitter effects. 2. Whenever a tranmitter keys up the MDC4800 protocol calls for bit synchronization (a sequence of 1010101010101010....). In the program this will result in receive bit clock synchronization. There is no need to specifically look for the bit sync. 3. Look for frame synchronization in raw bit stream so that data frames can be broken apart. Frame synchronization consists of a 40 bit sequence : 0000011100001001001010100100010001101111. If this sequence is detected (or 35 out of 40 bits match up in the program) the system is idling and the next 112 bit data block is ignored by the program. If the inverted frame sync is detected one immediately knows that 112 bit data blocks will follow. 4. Receive the 112 bit data block and undo the bit interleave. This means that one must reorder the bits in the following sequence : {0,16, 32,48,64,80,96,1,17,33,49,65,81,97,2,18,34,...} if the orignal sequence were received as {0,1,2,3,4,5,6,7,8,...}. 5. Check the convolutional error correcting code and count the number of errors. The error correcting code is rate 1/2 which means we will be left with 56 data bytes. The encoder is constructed so that the output consists of the original data bits interspersed with error correcting code. The generating polynomial used is : 1 + X^-1 + X^-5 + X^-6 Whenever an error is detected a counter is incremented. An attempt is made to correct some errors by finding the syndrome and looking for the bogus bit. 6. Keep receiving 112 bit data blocks until either a new frame sync is found or two consecutive data blocks have an unacceptably large number of errors. 7. Each data block consists of six data bytes; the last 8 bits are status bits that are simply ignored. The program shows the data in two columns - hexadecimal and ASCII. This data is kept in a buffer and is written to the file "data.dat" when the program terminates. 8. What the program doesn't do: As a further check on the data there can be CRC checks. This varies from protocol to protocol so this program does not implement the CRC checks. Nonetheless, it is a relatively trivial matter to find the generating polynomial. The addresses, block counts, and message ID numbers are also quite easy to deduce. As you can see, there is no encryption. The bit interleave and the error correcting coding are there solely to insure the integrity of the ASCII data. Since any moron could have figured this stuff out from scratch one could argue that MDTs do not use "...modulation parameters intentionally witheld from the public". Therefore the Electronic Communications Privacy Act may not prohibit receiving MDT tranmissions. However, consult your attorney to make sure. The total disregard for security will no doubt annoy countless Motorola customers who were assured that their MDT systems were secure. Since Federal law states that NCIC information must be encrypted your local law enforcement agency might be forced to spend millions of dollars to upgrade to a secure MDT system - much to the delight of Motorola and its stockholders. Cynics might conclude that the release of a program like this is timed to coincide with the market saturation of existing MDT systems. Also, this program is completely free and it had better stay that way. What's to prevent you from adapting this into a kit and selling it
from classified ads in the back of Nuts and Volts? Nothing. But take a look at Motorola's patents sometime. You'll notice that this program does things that are covered by a shitload of patents. So any attempt to take financial advantage of this situtation will result in utter misery.
Please keep the following in mind: this program only works with the first serial port (COM1). If your mouse or modem is there too bad. If you don't like this rewrite the program. ------------------------------------------------------------------------ What equipment do I need? RADIO SCANNER: A scanner that can receive 850-869 MHz. For those of you who don't know, this is the band where most business and public service trunked radio systems can be found along with the mobile data terminal transmissions. Chances are excellent that if your local authorities have a motorola trunked radio system and mobile data terminals that this is the frequency band in use. Very rarely will one find mobile data terminals in other frequency bands. Now for the fun part - your scanner should probably be modified to allow you to tap off directly from the discriminator output. If you wait until the signal has gone through the radio's internal audio filtering the waveform will likely be too heavily distorted to be decoded. This is exactly the same problem that our friends who like to decode pager transmissions run into - some of them have claimed they can only decode 512 baud pager messages using the earphone output of their scanner. These mobile data terminal messages are 4800 baud so I don't think you have a snowball's chance in hell without using the discriminator output. If you don't know where to begin modifying your scanner you might want to ask those who monitor pagers how to get the discriminator output for your particular radio. COMPUTER/SCANNER INTERFACE Those of you who have already built your interface for decoding pager messages should be able to use that interface without any further ado. For those starting from scratch - you might want to check out packages intended for pager decoding such as PD203 and the interfaces they describe. The following excerpt gives an example of a decoder that should work just fine (lifted out of the PD203 POCSAG pager decoder shareware documentation):
0.1 uF |\ +12v ---||-----------------------|- \| AF IN | |741 \ ---- | | /--------------------- Data Out | \ ------|+ /| | CTS (pin 5/8) | / 100K | |/-12v | or DSR (pin 6/6) | \ | | GND / ----/\/\/\---- GND ------ GND (pin 7/5) | | 100K | \ N.B. Pin Numbers for com port are GND / given as x/y, where x is for a 25 \ 10K way, y for a 9 way. / | GND
The above circuit is a Schmitt Trigger, having thresholds of about +/-
If such a large threshold is not required, eg for a discriminator output, then the level of positive feedback may be reduced by either reducing
1v. the
value of the 10K resistor or by increasing the value of the 100K feedback resistor.
The +/- 12v for the op-amp can be derived from unused signals on the COM port (gives more like +/- 10v but works fine !):-
TxD (2/3) --------------|<-------------------------------------- -12v | | RTS (4/7) --------------|<-------- GND - - | | _ + 10uF --------->|------- - - | Diodes 1N4148 | - + 10uF GND | | DTR (20/4) ------------->|-------------------------------------- +12v
If I were building this circuit I would strongly suggest tying the non-inverting (+) input of the op-amp to ground since you are working directly with the discriminator output and don't need a Schmitt trigger. All these parts or equivalents are easily available (even at your local Radio Shack which stocks the finest collection of components that have failed the manufacturer's quality control checks and supported by a sales staff that's always got the wrong answers to your questions). Also: DO NOT use the RI (ring indicator) as an input to the computer. ------------------------------------------------------------------------- How do I check things? As a first step, I would get a package such as PD203 and use it to decode a few pages. If you can get that working you know that that your interface circuit is functioning correctly. If you are in a reasonably sized town you might be part of the ardis network. The ardis network is a nationwide commercial mobile data terminal network where one can send/receive E-mail messages from one's portable computer. It has been exclusively assigned the frequency of 855.8375 MHz. Therefore, if you can hear digital bursts on this frequency you are basically guarranteed that these are MDC4800 type messages. You should be able to get stuff popping up on your screen although a lot of the messages will not be plain english. If your interface works but you can't seem to get any messages on the screen for a channel you know is a Motorola MDT system then it might be possible that your scanner/interface is putting out data with the polarity reversed. To check for this run the program with a command line arguement. When it runs you should an initial "Polarity reversed" message and hopefully then things will work out for you. Other than that: if this program doesn't work pester someone else who has got it working. Don't bother pestering the author(s) of this posting; the shit(s) aka "she/he/it (s)" are afraid of a thousand lawyers from Motorola descending like fleas to infest their pubic hair and accordingly have decided to remain forever anonymous. No doubt someone on the usenet who sees this post will know what to do with this program and also hopefully rewrite into a more user friendly form. When you do please don't forget to release the source code. ------------------------------------------------------------------------- Future projects/nightmares you might want to think about: Certain MDT systems embed formatting information in the text in the form of ESC plus [ plus a few more bytes. Someone might want to decode these on the fly and format the output so it looks exactly the same way as the user sees it. Make it so that this program works with com ports other than COM1. Make it user friendly? Enlarge the data buffer from the current 30k. Give the output data file an unique name each time the program is run instead of "data.dat". How about sorting through the past traffic so that you only see traffic to a specified user? The program does not cut data blocks off in the display but it might add an extra one or two (which will display as all zeroes). Someone might want to make all those zeroes be shown as blanks instead. Write some real instructions. Now the more ambitous stuff: Are you half-way competent with RF engineering? Then listen in to the tranmissions from the mobile units back to the base station. That way you get everyone's password and user IDs as they log on to the MDT system. By this point you will no doubt have been able to figure out all of the appropriate communications protocols so you should think about getting your own transmitter up and running along with the necessary program modifications so that you can transmit MDT messages. The required transmitter can be very simple - for example, those masocists who want to start from scratch might want to special order an appropriate crystal (pulling the frequency with the computer's tranmit signal), building a frequency multiplier chain, and adding a one watt RF amplifier to top it all off (see the appropriate ARRL publications for more information on radio techniques). Now you can log in and look at the criminal records and motor vehicle information on anybody you can think of. Find out what your neigbors are hiding. Find out who that asshole was that cut you off downtown. Find out where your former girl/boy friend is trying to hide from you. And on and on... Those with simpler tastes might want to simply transmit at the base station's frequency to any nearby MDT terminal - now you too can dispatch your local law enforcement agencies at the touch of your fingers!!! See your tax dollars at work tearing apart every seam of your neighbor's house. Or create strife and dissension in your local law enforcement agency as more and more officers come out of the closet using their MDTs trying to pick up fellow officers. There are municipalities that have put GPS receivers on all of their vehicles. Should it happen that the information is sent back over one of these networks you could have your computer give you a real-time map showing the position of every vehicle and how far away they are from you. Extend your knowledge to other data networks. Here you will want to look at the RAM mobile data network. It uses the MOBITEX protocol which is really easy to find information on. Since it is an 8 kilobaud GMSK signal there is a decent chance that you can use the interface described here. This transmission mode demmands much more from your equipment than MDT tranmissions. At the very least you must be much more careful to make sure you have adequate low frequency response. Despite this it is possible to receive and decode MOBITEX transmissions with a simple op-amp circuit! This just goes to show you what drivelling bullshit RAM's homepage is filled with - they explain in great detail how hackers will never be able to intercept user's radio tranmissions (incidentally explaining how to decode their tranmissions). The necessary program will be the proverbial exercise left for the reader. For better performance buy a dedicated MOBITEX modem chip and hook it up to your computer. ---------------------------------------------------------------------- A few words about the program: Remember - you must have your decoder hooked up to COM1. The RTS line will be positive and the DTR line negative but if you built the decoder with a bridge rectifier you really don't have to worry about their polarity. Stop the program by punching any key; don't use control-c or control-break! If you must reverse polarity run the program with any command line arguement (example: type in "mdt x" at the command line if your program is mdt.exe). You should then see the "Polarity Reversed." message pop up and hopefully things will then work. As far as compiling this - save the latter portion of this posting (the program listing) and feed it to a C compiler. Pretty much any C compiler from Borland should work. If you (Heaven Forbid) use a Microsoft C compiler you might need to rename some calls such as outport. Follow any special instructions for programs using their own interrupt service routines. This program is not object oriented. It also does not want anything whatsoever to do with Windows. Please don't even think about running this program under Windows. Finally, here it is: Good Luck and may God be with ya ************************************************************************** Subject: More real spy stuff... Germany smuggled agent out of Russia Germany's Federal Intelligence Agency smuggled one of its Russian agents to safety while Russian President Boris Yeltsin and German Chancellor Helmut Kohl were meeting in Moscow last Nov., the weekly news magazine Focus said Monday. The BND had received a tip that a long-serving Russian agent was threatened and launched a cloak and dagger operation Nov. 29 to pull the agent out of Russia. The agent, a 32-year-old Army captain from the Russian town Samara with the code name "Coastal Fog," had given BND Russian military communications secrets for years. The rescue operation took place as Kohl and Yeltsin sat down for talks. Russian spies still fighting the Cold War in Britain Security sources say Moscow is as eager as ever to uncover defence secrets But now it is acting more for economic than militaristic reasons. Security sources put Russian military espionage in Britain at the same level as it was in the 1980s. In a radio broadcast in December, President Yeltsin, speaking about Russia's intelligence aims, said: "Notwithstanding positive changes after the end of the Cold War, tough competition is still underway in the world. Competition for new technology and geo-political influence is increasing." Space Imagery Overhaul Aims at Better Data and Easier Access The shuttle flight is part of a massive modernization of the multibillion-dollar U.S. intelligence collection program. The goal is to compile a comprehensive view of the world from overhead -- using the shuttle, satellites, spy planes and missiles -- and to consolidate the data in a single computerized system accessible to civilian and military officials across the government. A CIA Target at Home in America By DANIEL C. TSANG Los Angeles Times January 18, 1998 Because of me, the Central Intelligence Agency has had to concede it does spy on Americans. Just last month, the agency had to remove a denial posted on its Web site that it doesn't do this. For it kept a file on me throughout the 1980s and '90s--despite a law against political spying on Americans. Just before Christmas, the CIA revised its Web site. The new version says the CIA can keep files on Americans if they are suspected of espionage or international terrorism. But I am no spy or terrorist. The CIA conceded as much by settling my lawsuit, paying my lawyers some $46,000 and promising to expunge my file and never spy on my political activities in the future.