Radius/Maxtrac/Maratrac Ham Conversion

I have had a Radius sitting on the shelf for some time. I didn't give it a lot of thought as I didn't want to hassle with Motorola's propriety programming. Then I started looking and thinking about what I could do with it. As I recall the radio had something wrong going on so I started by making sure the receiver would work well in the Ham band. I also had a second RF board for UHF. This radio has a VHF PA so I started with that.

The RF Board Connector

The start. June 17, 2014

First thing was to make a tool to work over the RF boards.

Radius RF Tool

This is a right angle header soldered to a piece of one sided PC board. I cut the lines with a Dremel cutoff wheel. Here it is with power applied.

Radius Tool in use

Because it lays flat with the board, it doesn't get in the way when flipping the board over.
So you can see two pieces of coax. The one going under is connected to the RX input port. the lighter one is tacked to the input of the mixer. The impedance here is very close to 50 ohms. Now I can sweep all the way through as the active device has power.

The Front End

I was suprised at how nice the VHF board looked. I was to understand that an HLD4322B was not a great Ham band board. But this is what I saw.


The marker is at 140Mhz and the sweep is 10Mhz per division. There is only the slightest tilt at 146Mhz. The UHF board was a HEL4435A, it did not look good at all. But the front end on this board had aluminium slugs in the coils. By backing them out I got this:


The marker is at 430Mhz and the sweep is 20Mhz per division. The big nasty to the left of the bandpass is the LO running dirty

The Synthesizer

The next go round. July 1, 2014

micro and rf board

On the left, red circuit board, is a Texas Interments Launch Pad. The whitish board is bare copper, and just like the RF plug, it has been cut with a Dremel enough to hold down parts. There is just a header and five one transistor level shifters, for now I'm just using the first three. The logic on the RF board is a full 9.6 volt swing while the MSP430 is 3 volts. Except for the VHF low band board, the synthesizer is a MC141558. It should be a direct replacement for Mot's RF division 84704M75. So far it looks like the low band chip was produced only for these radios. But once I bench a low band board I would expect the logic to work much like the commercial line of chips. So the cable off the RF board is hooked to fR, the pin 13 test point of the synthesizer. Pumped in a 2880 divisor to the ref counter

Referance Counter Input


Ref Counter

5Khz steps. The Launch Pad is a quick and easy way to start a project. Even if you move beyond the Value Line MSP430s, your code will port right over. Here is a link to the source for this first test.


The Synthesizer Part II

Sunday Fun. July 6, 2014

I wanted to finish up the synthesizer code. I'm getting a low band radio before long so the code will cover all the bands. The VHF wasn't a big deal, I knew what the commercial version of the chips where. I got thrown with the UHF board for a bit. They used a 127/128 prescaler and the MC12017 is a 128/129. So I was coming up off on the frequency selection. My hard copy of the maxtrac manual doesn't have any discussion but I remembered the manual on repeater-builder did. Sure enough they disclosed info about the prescaler and had a pretty straight forward formula that I just copied into my code, works fine.


Next is to measure and stash the temperature compensation voltages for the reference oscillator.

Thanks, Dan.

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jul 14