Batboard

According to the M1225 specs, in narrow mode, it uses 12.5kHz channel spacing.

The upcoming narrow band plan for railroads uses a 12.5kHz channel width, but 7.5kHz spacing. (http://www.ttci.aar.com/aar_rf_ms_info.php)

I'm assuming that the M1225 will be able to properly receive narrow band transmissions on current AAR channels (ex: Ch. 08 160.2300), but will it be able to tune the new splinter channels (ex: Ch. 108 160.2375)?

My confusion stems from the fact that many (including some Moto dealers who specialize in railroad communications) are stating that the AAR plan uses 12.5kHz *spacing*, and that the M1225 is compatible with the railroad band plan.

It would seem to me that half of that assertion is incorrect. I just need to know which half.

Thanks, and as always, my apologies if this is a stupid question.

I entered your freq 160.2375 in a M1225 codeplug and it accepted it ok. I also entered an invalid freq to test and it stated that the frequency must be an even multiple of 6.25khz, 5khz, or 3.75khz to work. Hope that helps.

ard099 wrote:I entered your freq 160.2375 in a M1225 codeplug and it accepted it ok. I also entered an invalid freq to test and it stated that the frequency must be an even multiple of 6.25khz, 5khz, or 3.75khz to work. Hope that helps.

Thank you, and yes that does help a lot.

It would seem that I'm not understanding how Motorola defines channel spacing, since your findings suggest that the M1225 is actually capable of channel spacings smaller than 12.5kHz.

Not sure if this helps you but I do know this,

the new 7.5 Khz channel spacing is not through out the entire VHF Hi band,
but only on various portions within the entire band.

I do not have enough info to tell you which portions have this new channel spacing.

I had wondered about this. It would explain why a fair number of people have looked at me like I was nuts when I asked about narrowbanding and 7.5hHz spacing. It may be peculiar to the AAR band plan.

When you are getting this technical, it is important to emphasis the difference between programmed channel spacing and bandwidth.

Make sure whomever you are talking to is in the same plain as you are.

Lastly, why would you want an older radio like the 1225 for FRA? Why not something much newer and capable of more than 24 channels?

com501 wrote:Lastly, why would you want an older radio like the 1225 for FRA? Why not something much newer and capable of more than 24 channels?

I volunteer at a railroad museum that has three separate radios scanning 3 different railroad frequency pairs. We need something that's compact, resistant to intermod and RF pollution, 12.5kHz selectable on a per-mode basis, and cheap. They're also far more plentiful than the narrowband GM300s.

The M1225s seem to fit that bill quite nicely, and even the lowly 4-mode models will scan.

Since they only need to monitor 2 frequencies and never transmit, anything more modern like a CDM would be total overkill.