Channel Spacing vs Tx Deviation

RailroadTech · Post by **RailroadTech** » Thu Jan 04, 2007 6:19 am

Ok I see a thread called Astro Saber 2.5Khz I am not sure what that means.

Here is what I know....

Channel Spacing 25Khz, Analog Deviation 5Khz Max, Astro Deviation C4FM aligned to 2.83Khz

Channel Spacing 12.5Khz Analog Deviation 2.5Khz Max, Astro Deviation C4FM aligned to 2.83Khz

Note there is no difference in digital mode between 25Khz and 12.5Khz deviation in digital mode. The explanation I got is simple in FM deviation is a function of the energy, talk louder get more Deviation but using C4FM this is no longer true, talk louder the encoded bit pattern changes but the digital pattern stays the same. So twice 2.83Kz is still only 5.66Khz no problem.

Now Channel Spacing 6.25Khz I never heard of any radio that is set set to what 1.25Khz Analog Deviation Maximum or do all 6.25Khz channel spacing radio have to be Digital? The Digital requirement makes sense to me. What about Deviation in Digital mode?

You know what Motorola will be doing for MOTOtrbo, each 12.5Khz channel will be divided into two slots giving and effective 6.25Khz channel spacing. Now MOTOtrbo is not Astro but it is digital and I would of thought that up coming Astro 25 Phase II subscriber may use the same trick.

I am not sure where the term Astro Saber 2.5Khz comes from must be talking about deviation? I was trained to always think in the terms of bandwidth requirement.

Any comments?

Am I wrong in anyway?

ai4ui · Post by **ai4ui** » Thu Jan 04, 2007 8:21 am

It has to do with the ability to program frequencies in 2.5 kHz steps, i.e.:

154.0000
154.0025
154.0050
154.0075
154.0100
154.0125
154.0150

It does & does not have anything to do with deviation. It does in that it allows you to be able to program a radio with new, refarmed frequencies that are 12.5 kHz deviation, but it does not in that the frequency steps do not set deviation levels.

Robert

Post by **batdude** » Thu Jan 04, 2007 9:37 am

wrong frequencies.

the 2.5k tag on the radio indicates that the radio RF board will accept 6.25khz spaced channels in 2.5k steps

i.e.

156.04375
156.03125

etc.

(those are two of the new maritime mobile freqs)

without that 2.5khz tag on the radio (or a retrofit to a narrow RF board) - the radio will not function on those freqs.

doug

The Pager Geek · Post by **The Pager Geek** » Thu Jan 04, 2007 11:45 am

New Maritime freq are: (based on yours listed)
156.4375 = ch268
156.3125 = ch206

Per gov site: http://www.navcen.uscg.gov/marcomms/vhfnb.htm

As for the steps...
The radio does BOTH 6.25Khz AND 2.5khz
154.00000 Start
154.00250 (add 2.5Khz)
154.00500 (add another 2.5Khz)
154.00625 (add 6.25kHz)
154.00750 (add another 2.5Khz to the previous 2.5khz freq)
154.01000 (
154.01250 (This is both a 2.5Hz and 6.25Khz step)
154.01500
154.01750
154.01875 (this is the 3rd 6.25Khz step from the start)

tpg

Post by **batdude** » Thu Jan 04, 2007 12:09 pm

no, you are not correct.

the ones i listed are the yet to be allowed channels 160 and 360

the freqs i listed are correct and are at the bottom of the web page you listed.

doug

RailroadTech · Post by **RailroadTech** » Thu Jan 04, 2007 12:54 pm

Thanks for the reply.

The Pager Geek · Post by **The Pager Geek** » Thu Jan 04, 2007 6:35 pm

batdude wrote:no, you are not correct.

the ones i listed are the yet to be allowed channels 160 and 360

the freqs i listed are correct and are at the bottom of the web page you listed.

doug

You are right... that's what I get for skimming the page...

MOT1 · Post by **MOT1** » Thu Jan 04, 2007 7:09 pm

pager geek:
I have been trying to get in touch with you for some time now. Please contact me via PM. Thanks!

Chris

Channel Spacing vs Tx Deviation

Channel Spacing vs Tx Deviation

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