Some Notes on the Motorola CM / PR Mobile Radios

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Back to Home Stretching the Frequency Range of the Motorola "Commercial Series" Radios
Researched, Compiled, HTML'd and Maintained by Mike Morris WA6ILQ

Back in January of 2020 I was asked if there was any way to use a VHF CM300 mobile radio made for the 146-174 MHz range below 146 MHz. A number of radios had been purchased for expanding a commercial fleet but the installation had been delayed (political reasons) and they were still in the boxes. An amateur radio special event was coming up and having a dozen extra mobile radios would be useful... The amateur radio repeater that the event was going to use was on a 145 MHz channel. I said "Maybe..." and one of the CM300s (model M50KQF9AA1AN) was handed to me, still in the box. I made a few phone calls and followed up on a couple of leads. Below is the result of the research and some office desktop experimentation on the CPS... I was not able to run the stretched radio past a service monitor. And I had to give the radio back so that it could be used for the event, and then reprogrammed with the fleet codeplug and installed in a fleet vehicle.

YOU CAN HELP ON THIS PAGE!
My only hands-on experience (so far) with tricking a Commercial Series radio to go out of range was the above experience with the one CM300 on VHF.
I'd be interested in YOUR results... both VHF and UHF. If I get any contributions with some hands-on VHF and UHF results from readers I will update this page with real-world numbers.

If you have a service monitor I'd be interested in what your receiver sensitivity and RF power is at 146.00 MHz, and at increments out of range... at 145.50, at 145.25, at 145.00, at 144.75, at 144.50, at 144.39 (the USA APRS frequency), at 144.25, at 144.00 and at 143.50 MHz. Does your transmitter RF power output change at those frequencies? Does the deviation change? Any other issues?

If your radio is UHF I'd be interested in your measurements of receive sensitivity and RF power in-range and at similar increments out of range, plus any other issues?

Thanks in advance. I can be reached via the page maintainer link above.

Mike WA6ILQ

The CM200 / CM300 / PM400 mobile radios and the CP200 / CP200XLS / PR400 portables were spec'd on VHF for 146-174 MHz but you might loose a little sensitivity and transmit RF power going below 146 MHz. Tricking the radio to operate out of the design range depends on the tolerances of the individual RF components inside the radio... most VHF radios will work down to 144 MHz. Most 438-470 UHF radios should work from 435 to 473 MHz, a few might not. An email reported that this process was successful in stretching the receive side of a 465-495 MHz radio down to 462 MHz receive for GMRS.

The CM200 and PM400 mobiles use the same synthesizer / controller design as the CM300 that I played with. The CP200, CP200XLS and PR400 are the portables in the same product line and should work the same (disclaimer: I have never had the opportunity to actually touch a CP / PR handheld much less program one). From emailed reports this process described below has been succcessful on both CM200 and PM400 mobiles, a UHF CP200 and a VHF PR400 handleld.

This procedure assumes that you:

Have RVN4191 CPS installed on your radio programming computer and know how to use it. The RSS help file says it runs under Windows 95, 98, XP and on Win7. I have an older Panasonic Toughbook that is dedicated to radio programming and it runs 32‑bit Win7sp1. I've not needed to try Win 8 and 10
Version R05.16 is one you want as it is the last one that allowed wideband or narrowband without a wideband entitlement.
Have a compatible programming cable for the CM mobiles or CP handhelds. See the "Updating your mobile cable" article on this page.
Have a hex editor on your computer and are familiar with using it.

Lets get get to it...

Read the radio with the CPS and save the codeplug as a file twice.... once as the working copy (you will be hex editing this one), and the second copy as a "just‑in‑case" backup that you hopefully won't need. If you screw it up you can copy the backup on top of your working copy and start over.
Open the working copy in your hex editor. Make sure it's in "overwrite" mode (i.e. not in "insert" mode).

Look at this translation of the codeplug elements:

Sort Sequence
Numerical Value	Codeplug Element Value
0 = A5	A0 = 5
1 = A4	A1 = 4
2 = A7	A2 = 7
3 = A6	A3 = 6
4 = A1	A4 = 1
5 = A0	A5 = 0
6 = A3	A6 = 3
7 = A2	A7 = 2
8 = AD	A8 = D
9 = AC	A9 = C
BB = "."

Find the hexadecimal sequence "BBA5A5A5A5A5A5". That's "BB" and six of the "A5". If you reference the table above that sequence translates to ".000000". You will find that sequence three times.
The first full entry in a VHF "K" range (146-174 MHz radio) is "A4A5A6BBA5A5A5A5A5A5". Look carefully at the first six characters - they will be "A4A5A6". This is the VHF synthesizer base frequency: 103.000000 MHz. Do not touch this one!
I do not know what the base frequency is for a VHF low range (model M50J...) radio (136-152 MHz) or for the 438-470 MHz or 465-495 MHz range UHF radios. If someone would be willing to let me know what they find then I'll update this writeup and add a table.
The second entry is "A4A1A3BBA5A5A5A5A5A5". This is the lower limit of a "K" range radio, "146.000000" MHz.
Those that are stretching a 146-174 MHz radio down to 144 MHz will be changing only the sixth character... "A4A1A3BB" to "A4A1A1BB".
Those with UHF radios will need to make the appropriate changes for their situation.
If you are going to contribute some real world sensitivity and power measurements to this page (i.e. down to 143.0 on VHF) please consider using 143.0 MHz for your new low end.
The third entry is "A4A2A1BBA5A5A5A5A5A5". This is the upper limit, "174.000000" MHz. I can't imagine why a ham would be changing this one, the RF components in the radio will not do 220 MHz.
Save the hexedited codeplug file. Just overwrite your working copy on your hard drive. This will be the starting code plug for your out-of-band radio.
Exit the hex editor.
Start the CPS, verify that you can read the radio, but then load your working copy.
Add your new frequencies in the 144-145 range. If your radio came from commercial service then it will probably be narrowband on all existing frequencies; don't forget to set your new frequencies to whatever is appropriate.
Write the codeplug with your new frequencies into the radio and... THIS IS IMPORTANT ‑ Save the codeplug to your hard disk with a filename that you can find again.
When you need to change the programming in this radio DO NOT read the radio!!!
Somehow the modified codeplug is still telling the CPS that it's still a 146-174 MHz radio ! If you download the radio the CPS will think all of the 145 MHz frequencies are errors, it will "fix" all of the out of band frequencies. The end result is that you will have to re‑hex‑edit the codeplug from scratch and re-enter all of the below‑146 MHz frequencies. This is the voice of experience !
Instead of reading the radio just load the saved codeplug into the CPS, make the necessary changes, and then write them to the radio. Just treat this radio as a write-only device.

There has to be a better way where we can change the band edges in the radio so that the CPS does not "fix" the out of band frequencies when downloaded but I've not been able to figure that out as I don't have a radio... Maybe the codeplug includes the model number? Maybe there is a model number to frequency range table in the CPS? I do not know.

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This page was created 13-Nov-2023 by Mike Morris WA6ILQ.

This web page, this web site, the information presented in and on its pages and in these modifications and conversions is © Copyrighted 1995 and (date of last update) by Kevin Custer W3KKC and multiple originating authors. All Rights Reserved, including that of paper and web publication elsewhere.