33 cm questions...

[Jonathan KC8RYW]

I was hoping to gain some input from those on the board regarding 33 cm.

Here are some of my main issues:

<b>12.5 KHz or 20/25 KHz?</b>

All Motorola gear comes built for 12.5 KHz, however, most plans will suggest conversion to 25 KHz.

I am tugging between both.

25 KHz means better audio, but more bandwidth.

12.5 KHz means typically reduced audio quality, but uses less bandwidth. Being that most of 33cm isn't firmly rooted yet (at least from my viewpoint, in my area), it would be nice to use less bandwidth, to allow more users, from the get-go, to avoid possiable "cramming" if/when 33cm gets popular.

Which to use?

<b>Band Plan Variations..</b>
This is the biggest annoyance. From my observations, places where 33 cm repeaters seem to exist, the bandplan calls for inputs at 902 - 903 and outputs at 927 - 928 (thus 25 MHz spacing.) This allows for better results from commercial gear, and also, allows for better seperation in duplexing.

HOWEVER: the frequency coordinator in the state where I reside decided to loosely follow ARRL's frequency bandplan, and put inputs at 907 - 910, and outputs at 919 - 922 (12 MHz spacing.) Not so amazingly, given these restraints, there are no LISTED or COORDINATED 33 cm repeaters in the entire state of Michigan.

SO, what should I/we do? Say "heck with you!" to the coordinator, and run contrary to local bandplans, and never be able to have the machine be coordinated, OR follow the bandplan, and go insane trying to make it all work with commercial gear and tighter rx/tx spacings in duplexing?

I think these are two of the biggest issues facing 33 cm, other the fact that coax loss is a real killer at 900 MHz.

Oh, AND THE FACT THAT THERE IS NO REAL COMMERCIALLY AVALIABLE 33 CM HAM RIG!

[n1pfc]

12.5 KHz is usually enough for audio based voice communications (if you really want, run SSB on 900MHz =) ). I actually have my JT1000 set up for narrow band at it works fine on all of the 2M repeaters I use. You could stay with 25KHz channel spacing as well, but if you're restricted to 5KHz deviation, you're going to be withing the 12.5KHz spacing anyways. The only issue that you may have is some 'bleed over' from transmitters that are over deviating or from the front end filter skirts not falling off fast enough for a near by transmitter.

Commercial split for 800/900MHz is typically 45 MHz, so 25MHz spacing makes more sense to me (45MHz puts you outside the band on at least one side). Of course the other thought is that with that much spacing you severely limit the number of repeaters that you can have in a given region. That may have been your local coordinator's idea when he set up for the 12MHz spacing for the inputs and outputs of the repeater.

Of course, you don't *HAVE* to follow the band plan, especially for repeaters. It's a suggestion. I know a couple of 2M repeaters in my area here that have odd splits to them. The splits still fall within the repeater input / output ranges, but it's not the standard 600KHz.

You should still coordinate the repeater though, even if you decided to use what your coordinator deems as an 'odd' split. You don't want someone coming along and trying to grab your frequency from under you. If it's coordinated and the other one isn't, you have priority.

Kurt

[ARZ902]

There is a "900 Mhz HAM" board that you might want to check into.

[email protected]

All the questions you asked have been discussed.

Dennis

[Jonathan KC8RYW]

There is a "900 Mhz HAM" board that you might want to check into.

[email protected]

All the questions you asked have been discussed.

Dennis

Thanks, I joined it. I'll try looking through the archives.

[N9CZV]

I have 4 900mhz repeaters running and I find the narrow band great.


David Epley, N9CZV
Show Low, Az