Modifying Motorola RSS and CPS Out of Band

Modifying Programming Software - Benefits and Pitfalls

People often hex-edit their programming software. The two major reasons are to allow entry of amateur frequencies and to increase the number of available channels/modes. For example, GTX software only allow 10 conventional modes, but the hardware is capable of at least 15.

The modifications often take place in a Model Definition File, a file with the MDF extension. These files are usually small and version-dependent, so you can not take an MDF file from R01 software and expect it to work with R04 software. In addition, the program reads the MDF file and adds all the byte values together, a process called "generating a checksum". It then compares that total with a known value stored in the program; if the two don't match, the software will complain and usually not let you proceed any further. This revelation often doesn't happen until after you've read the radio's code plug, and the program tries to find the model number in the MDF file but won't due to the checksum mis-match.

Some changes may have to be made in other files. For example, SPECTRA1.EXE is where the frequency limitations are maintained. This data is also controlled by a checksum, so once again it's important that if you alter bytes in one area, you make corresponding changes in another, less important area. Text messages are prime candidates for fixing checksums.



Whenever you make a change to an MDF file, it's imperative that the checksum be the same before and after you hex-edit it. If you raise the value of one byte, you must lower the value of another byte. Often some of the text messages are altered in the process of correcting the checksum. If you do this, try to choose a message that would never be seen when programming the radios you have. For example, the GTX MDF file contains several strings with the words "MaxTrac" and "Radius" in it, which can readily be trashed to get the checksum right.

Also remember to make, and put away in a safe place, a backup of any original files you hex-edit. If the changes you make don't work, you may want to start over. Some hex-editing software gives you the ability to create a backup. It's always better to do it yourself and make the file name unique.

Making modifications to the software, and using it to program a radio, is fine as long as you are the only person who will ever own and program that radio. But, down the road, you may find that you prefer to sell this radio and acquire a different one. The next owner now ends up with a non-standard radio, and the standard unmodified software may not be able to read it. This is especially true if you've increased the number of conventional modes on a GTX radio. Stock software only expects 10 conventional modes, and if it finds more, it is not prepared to deal with that condition. It will usually complain about the code plug or radio model number, and you won't be able to go any further.

So here you are, the new owner of a radio with 15 modes and you only have stock software. If you take the radio to a commercial shop, they'll try reading the radio with their standard software and have the same problems you did. They won't want to hex-edit it just to read your radio, and in fact doing so will probably violate some copyright or licensing agreement they signed with Motorola. So you're back to square one.

You could obtain a hex editor and attempt to modify the software yourself. Some people are willing to do that, others won't and often try to take the easy route: find someone who has already done it and ask for a copy. This may be received with mixed results, so be careful who and how you ask.

All is not lost however. You just need to acquire a copy of the software that was modified in the same way that the previous owner used to write the code plug to the radio. That's not always possible, and you may have to send the radio back to the previous owner and have him/her reduce the number of modes to 10 or less. If you're lucky, there will be a GTX guru somewhere in your area who either has modified his copy of the programming software, or will be willing to do so. He/she can read the radio, delete some of the modes to bring it back to stock, and write the code plug back. Now you should be able to read the radio and do further programming using stock software.

Then you discover that you have version 1 software while the person - who fixed the radio's code plug for you - used version 4 software. The software version is written to the radio every time a code plug is written out, and an earlier version of software will not read a radio that was written with a later version of software. Now you're back in the same boat you were in a few days ago, but you're further up the creek, and still don't have a paddle.

This "software version incompatibility" problem has been around for quite some time, and it's not limited to us poor amateurs. When a radio is sent back to the Motorola depot for repair, they usually read the code plug, upgrade the firmware, and write the code plug back to the radio, all with the latest software. When you get the radio back, you discover that the slightly older software that you got when you bought the radios (it was in the contract that you get a copy) won't read the repaired radio. You call Motorola and complain. They just tell you to buy the latest programming software; it's your problem now.

So what are your choices? The best thing to do is NOT modify the programming software in such a way that regular, unmodified, stock software can not at least read the radio's code plug. This means, unfortunately, that if the radio only has 10 conventional modes, you should leave it that way, or at least reduce the number of modes to 10 if/when you sell the radio, so stock software CAN read the radio. There are other, less legal options, which will not be mentioned here. Hex-editing to allow amateur frequencies is a necessity in order to use the radio. These changes at least won't hurt a future owner's ability to read and write the radio's code plug with anyone's stock software.