6m Mobile Radio Conversion Project

[mbalntel]

FWIW.... As part of getting a 6m repeater on the air, I've had thoughts of getting a conversion project going to get 6m mobiles spread around at a lower cost than new ones. I've been working on learning how to convert Motorola Maxtrac VHF-Low band mobiles with the correct 42-50 MHz band split to the 6m ham band; there is a lot of good info on www.repeater-builder.com for doing this.

There are a batch of correct band-split, VHF-Low band Maxtrac mobiles, 16 channel capable, for sale currently on eBay at $30 each, which includes shipping. Mics run about $15-20, 10' power cords with fuse for $11-12 (plain pigtails are just a few $$), a UHF-F to mini-UHF-M coax adapter for $5-$10, and MFJ makes a low-cost, dual band 6m/2m mag mount for $27+shipping from AES. So, we are are talking in the neighborhood of $100 before any mods, without any special bargains on any items. There will be likely another $10 or so in mod parts, plus figuring out a mounting method. The cheapest new 6m single band mobile I know of is made by Alinco, and costs in the $250 range (includes shipping). I don't intend to charge anything for the conversion; this is just to promote 6M use locally, and that will work as long as it does not become personally burdensome.

Maxtracs for this band are typically 60W; I would detune to 40-50W for lower heat in ham mobile use where we tend to be more long-winded. Disadvantages over a regular ham unit: Channels, PL tones, and squelch levels are programmed with special Motorola software, and power and deviation are set in firmware; you don't have front panel controls for those in a commercial radio like in a ham radio. Mods are available for power and deviation settings with pots inside the unit rather than firmware. (Perhaps a manual, front panel squelch pot can be added too; I just have not checked that out.) And the overheating is limited by a PTT timer not a temp sensor. That timer can be set up to 255 seconds; when it cuts out, you're just off the air for a time, rather than the power being reduced to 5W in steps for thermal protection. (FYI, later GM300 series mobiles have a temp sensor heating protection scheme, like modern ham mobiles.)

Where this stands: I have one Maxtrac mobile from the ebay site, which was pretty clean out of the box and tests out fine for transmit power and recceiver sensitivity. I have the radio service software and interface up and running with an old PC.
Steps in this next month are to:
- Find out how much interest there its for such units; reply here or to my email
- See if any others want to volunteer to help in the project
- See of there are better units to convert
- Follow the circuit conversion processes for the Maxtrac from Repeater Builder and get a unit converted to 6m
- Explore either putting in manual power and deviation setting pots (and perhaps a front panel squelch pot), or sticking with firmware for this. There are 2 firmware options for this: buy a pre-made chip firmware EPROM chip from ebay for $19, or figure out the way to change the firmware and program EPROM's locally. (There is some support info on Repeater Builder for the latter.)
- Figure up site list(s) to program into the mobiles
- Look at ways to get more than one computer up with the RSS programming software

I would like to get some feedback on interest in this from other local hams. If it is something of solid interest, then either individual purchases or group buy of parts could be made to meet the commitments and maybe a couple of us could get together for a mobile conversion 'party', or figure up a way to efficiently split the conversion tasks.

Anyone wanting to get a unit, please let me know. And anyone wanting to learn and help and take a part of the process, that would be good too. (I travel a lot for work so my time is limited.) Doing a batch conversion is the goal, to be efficient. And if there are better mobile units to convert, that would be good too. I just glommed onto the Maxtrac's since they are available in quantity right now for a good price.

Another item of interest is what channels to program. Candidate sites: the new local 53.41, the Lexingtion area 53.01, Roanoke/Poor Mtn, Oilville,and Snowshoe are active 6m sites that I am aware of in this region. There can be more more than one programming list.

This is a bit of a long term project, to be worked in as time and life permits, but hopefully a useful one.

Tnx es 73's, Mark B. NM9S, Afton VA