Batboard

Stupid question, and I'm pretty sure I already know the answer:

Is there any way to get a Maxtrac 900 to monitor (no transmit) on a 6.25 kHz channel spacing? For example: 932.36875 or 941.36875.

I know those are slightly out of band, but after entering the nearest available step for each frequency, the steering line voltages are well within spec.

I'm guessing it's an impractical idea for the same reason trying to get a VHF Maxtrac to do 12.5 kHz spacing is impractical, but I thought I'd ask.

If the Maxtrac can't do it, are there any other older (read: affordable) 900mHz radios capable of tuning with a 6.25 kHz step? I've never handled anything other than a Maxtrac.

Thanks in advance.

I don't think so. The radio keeps track of the operating frequency as some number of 12.5 kHz steps above a base frequency (around 894 MHz). You'd have to alter both the firmware and programming software to handle steps of half that size. 800 MHz radios have the same step size but use a different base frequency (around 800 MHz) and they would have the same problem.

Even with different firmware and software, the hardware still might not be able to do it.

Bob M.

That's what I was afraid of based on our prior conversations, but I figured I'd take one last shot in the dark.

This also seemed like a good place to see if there are any alternatives to the Maxtrac that won't cost more than my car. I have some MDS units that are capable of operating on that frequency, but the ability to only monitor one channel limits their usefulness in a mobile installation.

I know the 20/25/30 kHz spaced SM50/SM120 radios WON'T do 2.5 kHz freq steps. The programming manual says all freqs must be divisible by 5 or 6.25 kHz.

Maybe an M1225 or something newer, which implies something more costly and less hackable.

Bob M.

I'm guessing this is for ATCS monitoring?

The MCS2000 might do it, but you can only get muted/de-emphasized RX audio out of them without tapping the board somewhere.

Yeah, probably for the US&S Genisys system that UP uses. To make it worse they also use a bunch of frequencies, requiring many radios to get good coverage. Most of the former BN lines use ARES which uses a common VHF channel in the AAR allotment. Much easier to monitor!

I'd be interested to know as well if anyone knows of any radios (read not scanners) that do this without much trouble.

Yes, Genisys monitoring is what I was looking into. I was so concerned with getting the Maxtrac into the proper range, I never considered the smaller tuning step. So close yet so far.

Modifications for "standard" ATCS monitoring have become old hat, I was looking forward to trying something new. Oh well, as you noted, there's always ARES.

This probably isn't what you want but, I remember when I was doing some Visar hacking that the frequencies are multiples of 6.25 KHz. I seem to remember actually programming one such frequency in just to see if it took. The Visar probably isn't usable for what you want to do, however and I can't say with 100 percent certainty that they will take 6.25 KHz frequencies. If you are interested, give me a few days and I'll check. This is a 900 trunked RF board mated to a conventional controller and tricked into believing it is a 900 conventional.