MDTW1234 Frequently Asked Questions

Written by SirValence / Spectrum Analyzers

This FAQ will be updated as more questions are asked.
Updated: Nov 7/98

I have re-printed this paragraph from our "About Us" page: "Intercepting some comms requires specialized, modified, or custom monitoring equipment and software, and the author assumes that anyone wishing to monitor these comms has access to, or has the technical ability to construct or modify, this equipment and software."

What is MDTW1234?
MDTW1234 is a software package which, with the right hardware, will allow someone to monitor Motorola's Mobile Data Terminals (MDTs) which use the MDC-4800 protocol.

Who wrote it?
The original MDTSTUFF C code was posted to the alt.radio.scanner newsgroup by someone calling himself lord@heaven.com. Some code correction was done by arron5@trap.geocities.com. The new enhancements were written by Bonzo of Spectrum Analyzers.

What are these "enhancements"?
MDTW1234 Rev.B supports the following options, via command-line switches:
1.) Support for Com1 through Com4. Default is Com1.
2.) Normal screen, normal log (hex/ASCII screen, hex/ASCII log; default)
3.) Wide screen, normal log (ASCII screen, hex/ASCII log)
4.) Wide screen, wide log (ASCII screen, ASCII log)
5.) Inverted data input
6.) Data pass-through to a second computer via the same serial port
7.) Online help

What is the current revision?
Rev.B is the current revision, released Feb 15/98.

How do I run it?
Create a sub-directory on your hard drive, and unzip it there. Run DRIV1234.EXE. DRIV1234 runs MDTW1234 repeatedly, saving, appending, and time-stamping the log file as the buffer fills up. We have used the date as the log-file name for easy reference. This allows you to run the package unattended for days and review the log file at your convenience.

It doesn't work! What do I do?
First, we need to determine exactly which part is not working.
Serial port:
Are you addressing the correct serial port? Use the command-line switches to try a different com port.
Is that particular serial port working? Check it with a mouse. Make sure the connector inside the computer has not come off.
Is there a conflict with the serial port and another device? Try disabling / removing the suspect peripheral (ie. modem), or try a different com port.
Interface cable:
Use an ohmmeter to check for continuity and shorts. It's pretty tough to make a mistake here.
Serial cable:
Make sure you have a SERIAL cable, and not a NULL-MODEM cable.
Check all of your connections. Check them again. Make sure the polarity of the diodes and the capacitors are correct. Make sure you didn't plug the IC in backwards. Try a different IC. Check for solder bridges.
Try inverting the data input. I have to do this in my area.
Make sure you are running from DOS, not from a DOS window inside Windows. It should work with MS-DOS 2.11 or newer.
Are you set up for Listener/MDT?
If you are having trouble getting MDTW1234 running, make sure that you select "N" when you see the question "Do You Want Intercepts Sent To The Comport? (Y or N) " or that you do not use the "/OUT" command line argument. If your Listener/MDT program is not running, or your cabling between the MDTW1234 machine and the Listener/MDT machine is incorrect, the MDTW1234 program will halt until the cabling is fixed or Listener/MDT is running. In other words, verify your MDTW1234 runs correctly before adding the Listener/MDT component.
Do you have a friend with a working system? Take your interface and cables to your friend's working station and try it out there, or bring your friend's working interface and cables to your station. Swap items until you isolate the problem.

Everything seems to be hooked up correctly, but I don't see anything on my screen.
Try inverting the data.
Check the signal strength; is it strong enough? You may need to run a gain antenna.
Perhaps the RFI from your computer is desensing your receiver. Try moving your internal antenna, or using an outside antenna.

I see things on the screen, but it's garbled / not readable.
You may be getting RFI from your computer; try moving your internal antenna or running an external antenna. Re-route the interface and serial cable. Re-route the computer cables.
You may be seeing files / pictures / GPS coordinates. Wait and see if other info appears.
Are you using a cheap RF amp to boost your signal? Try removing it, as it may actually be degrading the 800MHz signal.
The data you are receiving may be encrypted, in which case you are out of luck.

It's a simple freeware utility (written by Bonzo) for scanning your MDTW1234 log files for keywords. You can create a list of keywords (such as riot, hostage, ert, your license plate, etc.) and MDTSCAN will slide a 200-character window along the log file, displaying any found keywords in the 100th position. It is not included in the MDTW1234 zip file. Note: MDTSCAN is VERY slow. If somebody wants to write a faster version, please do so!

What is Listener/MDT?
Listener/MDT V1.1 is a beta Windows program which receives data sent from your MDTW1234-equipped computer and displays it in a window on a computer running Windows 3.x or Windows 95. Future development is planned for this software; the beta version is included in the MDTW1234 Rev.B package for testing purposes. You must be using the modified data-slicer interface as described on the Projects page.

What kind of radio receiver can I use?
You can use any scanner or receiver that receives narrow-FM on 800 MHz. We have been successful with the following: Icom R-100; RadioShack PRO-43, PRO-2005, PRO-2006; and Uniden SportCat (although the SportCat doesn't appear to be too sensitive). Best results will be realized with an external 800 MHz antenna.

What frequency should I use?
That depends on what frequency your local MDTs are on. In our area, they are on 859.5125 MHz. Check the frequency databases, frequency books, or scanner lists for your area. Check the Ardis frequency. Or use a frequency counter if you just happen to be within range while one is transmitting.

Does MDTW1234 work with the 150 MHz or 400 MHz MDT systems?
To my knowledge, the MDC-4800 protocol is utilized by Motorola's 800 MHz RF modems only; therefore MDTW1234 will not work with the 150 MHz and 400 MHz MDT systems.
Updated Nov 7/98: Apparently, there are some systems (such as Northern Illinois Gas) which use MDC-4800 in the 450 MHz, and MDTW1234 will decode the calls.

What kind of interface and cabling do I need?
Complete instructions are posted on the Projects page. They detail everything you need to know to build the All-In-One modified data-slicer interface to take advantage of current and future MDTW1234 revisions. I built mine on a piece of perf-board, and installed it into a gender-changer case. I installed a sub-mini earphone jack in the case, and an identical one on the back of my PRO-2006 for the discriminator audio output. You will need to fabricate a 2-conductor cable (data and ground lines) to connect your scanner to the interface (unless you install the interface inside the scanner). And you will need a serial cable between the interface and your computer. Keep everything shielded to reduce RFI and TEMPEST emissions. Construction assistance is provided in our help file.

Do you sell interfaces, kits, or cables?
Sorry, we just don't have enough extra time to build and test units in quantity, with our Projects, our other hobbies, our regular jobs, and our daily lives.

Where can I buy the parts for the interface and cables?
Most electronics supply places will have everything you need. RadioShack will have all the components, but be prepared to pay a bit more. I found all the components for my own interface in my spare-parts bin. The interface cable will depend on what you use for jacks; my cable has a sub-mini earphone-type plug on each end. The serial cable is a standard cable found in any computer store. You can buy a 25-pin gender-changer for use as a case at the computer store as well; just make sure that it is the type that can be disassembled, and that it has a 25-pin female connector at one end. The units with the metallized shielded plastic cases are the best.

Can I use the earphone or external speaker jack?
No. The earphone jack is ok for lower-speed applications such as 1200 baud POCSAG, but is not reliable for higher data rates due to filtering in the audio circuit. The proper way is to tap the unfiltered audio off the discriminator IC.

Which chip is the discriminator IC, and which pin should I use?
Check the list on the Projects page. It contains a listing of popular scanners, discriminator ICs, and the relevant pin. Use a shielded cable to run the tap to the jack; attach one end of the shield to a ground point close to the discriminator, and the other end to the outer connector of the jack.

What if my scanner isn't in the list?
The discriminator chips in the list are the most popular chips, and chances are your scanner uses one of them. Look at the chips in your scanner, and see if you can find it on the list; it will use the same pin as the listed scanner.

What else can I do with the interface?
With the right software, the interface will allow you to monitor Motorola's MDC-4800 MDTs, Ericsson's Mobitex MDTs, POCSAG paging, Motorola trunking data, EDACS trunking data, packet, RTTY, WeFax, CW, and other data modes. If you are using the modified data-slicer interface, then you can also get into Trunker two-scanner-mode applications where the discriminator output from one scanner tuned to the control frequency is used to tune a second CI-V or RS232-capable scanner. See the EDACS and TRUNKER documentation. To paraphrase Microsoft, what do YOU want to hear today?

Note: If you are planning to tune an Optoscan 456 using the modified data-slicer interface, remember that the 9-pin cable that Optoelectronics provides with the OS456 is a null-modem cable. Therefore, if you are building an interface to use with the OS456, you should not build a null-modem into your interface housing. If you've already built the interface with the null-modem inside it, all is not lost. Just connect a second null modem between the OS456 and your interface. This will give you a series of 3 null modems; two will cancel each other out, leaving one, which is what you need. Additional notes are contained in the All-In-One documentation.

What kind of computer can I use, and what does it need to have?
MDTW1234 is written for an IBM-compatible, running MS-DOS. Running it as a DOS task from Windows 95 won't work. I have used the MDTW1234 software reliably on everything from a 386-DX/33 to a Pentium 200 MMX. The computer needs to have a serial port, any mono or colour video card, and a hard drive for logging purposes (at least 50 MB; I can log 15 MB in a 24-hour period at my location). A mouse is not required. Yes, you finally have a use for all those outdated computer parts you've been accumulating! Listener/MDT will run in Windows 3.x or Windows 95. We have had one report of MDTW1234 being run on a Mac PowerPC on Com-2.

The Motorola modems support 19.2k as well as 4800 baud. Will MDTW1234 support the higher speed?
No, MDTW1234 does not currently support 19.2k RD-LAP protocol.

Do you work for Motorola?
We are not, and never have been, members of the Motorola Party.

Can I get tech support from you?
No. This package is freeware, so you get what you pay for. Anyone with basic electronic and computer experience will be able to get this package to work. If you don't have this basic knowledge, you should be asking a friend who has it for some assistance.

Are you planning any more upgrades for MDTW1234?
Yes. If and when they are released, they will be posted on our web site here. Stay tuned.