6.25 channels

[radioman2001]

I have been pouring over FCC dockets for about 2 hours now, and I am not finding what I am looking for. I am in the middle? or beginning of designing a trunked radio system for my RR. AAR's coordinator TCI has made it known that they are NOT allocating any new channels, until the change over to 6.25. Now that in itself is not a problem, but they are saying that the FCC is mandating that you have to have DIGITAL radios to work on the 6.25 channels. I can't believe that this is true. From an operations standpoint, Motorola's 900mhz trunking systems were on 6.25 channels with 2.5kc deviation analog, and they worked just fine. What I am really looking for is the docket number or reference that states you MUST use digital scheme to get the 6.25 channels. My personal opinion is that it is not necessary and considering that most everyone who has used digital radios in noisy enviroments has not been happy, even to the extent of going back to their old analog systems. Does anyone have the specifics? Any help would be appreciated.

 

[N_Jay]

900 MHz is 12.5 kHz not 6.25 kHz.

The only analog that would fit (in the commercial world) 6.25 would be ACSB, and that stuff is dead.

 

[radioman2001]

Alright, maybe I am missing something, but if you have 2ea 2.5kc deviation channels next to one another, that should be roughly 5kc total. That should fit in a 6.25 spacing, shouldn't it?

 

[wa8pyr]

I have been pouring over FCC dockets for about 2 hours now, and I am not finding what I am looking for. I am in the middle? or beginning of designing a trunked radio system for my RR. AAR's coordinator TCI has made it known that they are NOT allocating any new channels, until the change over to 6.25. Now that in itself is not a problem, but they are saying that the FCC is mandating that you have to have DIGITAL radios to work on the 6.25 channels. I can't believe that this is true.

There is no mandate to go digital, no matter the band. That is a common misconception, especially in the public safety bands.

The only requirement is that equipment be narrow-band capable. Everything has to be capable of 6.25 kHz bandwidth; in the UHF bands the channels will eventually be on 6.25 kHz centers (ie 452.9375, 452.94375, 452.950, 452.95625, 452.9625 and so on), while in the VHF band the channel centers are now 7.5 kHz (160.230, 160.2375, 160.245, 160.2525, 160.260 and so on).

 

[N_Jay]

Alright, maybe I am missing something, but if you have 2ea 2.5kc deviation channels next to one another, that should be roughly 5kc total. That should fit in a 6.25 spacing, shouldn't it?

When you FM modulate a carrier you generate sidebands that extend beyond the deviation.

 

[radioman2001]

I understand about the need for guard bands, this was hypothetical description. That would leave 1.5 kc total for guard band for 2 channels, or roughly 750hz between channels. As far as the dictum about going digital, I raised that question also, that's why I am looking for the definitive answer about going digital from the FCC not the coordinator. If it's not there I am going to apply for about 30 pairs with 2.5kc analog deviation until technology catches up to make digital work right. It's not right to hold all these channels hostage for another 20 or so years until digital works with the same audio quality and background noise rejection as analog

 

[N_Jay]

I understand about the need for guard bands, this was hypothetical description.

We are not talking about guard bands. I am talking about OCCUPIED spectrum.

It may be time to do some background reading on FM modulation.
http://www.sfu.ca/~truax/fmtut.html
http://www.fas.org/man/dod-101/navy/docs/es310/FM.htm
http://en.wikipedia.org/wiki/Frequency_modulation
http://contact.tm.agilent.com/Agilent/tmo/an-150-1/classes/liveFM.html
http://www.arrl.org/tis/info/pdf/8505023.pdf
Lost more here:
http://www.google.com/search?hl=en&q=FM+Modulation&btnG=Search

That would leave 1.5 kc total for guard band for 2 channels, or roughly 750hz between channels.

Nope, your math is to simplistic.

As far as the dictum about going digital, I raised that question also, that's why I am looking for the definitive answer about going digital from the FCC not the coordinator.

There is no dictate to go Digital, there is also no current dictate to go to 6.25 kHz.
6.25 is coming (no date certain yet), and to my knowledge there is no one building or planning to build 6.25 analog equipment.

If it's not there I am going to apply for about 30 pairs with 2.5kc analog deviation until technology catches up to make digital work right.

Those would need to be 12.5 kHz channels. However you could probably live with 6.25 offsets as long as you have some geographic separation between the adjacent (and 1/2 overlapping) channels.

It's not right to hold all these channels hostage for another 20 or so years until digital works with the same audio quality and background noise rejection as analog

The background noise issue is overblown. It is mostly reported by the fire service, and in many of their test cases showing digital not working, analog was useless also.

 

[radioman2001]

So what you are telling me is dictum ? That there is not a requirement to go DIGITAL, with 12.5 and especially 6.25 channels spacing. Well I hope the not having to go digital goes over well enough with the coordinator, so I don't have to go over his head to the FCC, for my application. We are in the most congested RF spectrum area of the country so I am trying to be ahead of the curve, also I am a firm believer that if you don't use you WILL lose it (frequency's) .
My understanding on FM and sidebands is a little rusty, I will go through the sites you listed. Thanks for the information.

BTW have you seen the AAR ver 3.2 band plan?

 

[N_Jay]

So what you are telling me is dictum ? That there is not a requirement to go DIGITAL, with 12.5 and especially 6.25 channels spacing.

Not that I have seen, or heard about.

AGAIN, the practicality of 6.25 kHz analog is highly questionable.

Well I hope the not having to go digital goes over well enough with the coordinator, so I don't have to go over his head to the FCC, for my application.

I am not as familiar with the RR service, but in some cases (700 MHz Public Safety) the coordinator, or more specifically the RPC "is god" and going to the FCC only gets you sent back.

We are in the most congested RF spectrum area of the country so I am trying to be ahead of the curve, also I am a firm believer that if you don't use you WILL lose it (frequency's) .

Where are you?

My understanding on FM and sidebands is a little rusty, I will go through the sites you listed. Thanks for the information.

No problem.

BTW have you seen the AAR ver 3.2 band plan?

No, I have not done any RR work in a while.
I know guys that are very active on RR projects.

 

[radioman2001]

I am not really prepared to let out where I am yet. As far going to the FCC over the coordinators, I have done it 3 times and each time I got what I wanted. You just have to make your case, that shows the coordinator is being unrealistic and restrictive in not allocating the channels requested. I am not interested in 700, let someone else deal with that mess, I just read the LA county is not going to it and has requested the entire TV channel 15 (ala NYC and channel 16). The coordinators need to be made to understand that they are only recomenders, not gods. I was licensing channels before coordinators existed, and you think they are bad, you should have had to deal with the FCC directly back then.

 

[seligman]

I don't understand why the RAILROADS need to go to 6.25 kHz spacing.

12.5 kHz spacing is going to DOUBLE the number of available channels. Why would they ever need more? For the most part, the railroads do fine with ~90 channels.

 

[burner50]

I don't understand why the RAILROADS need to go to 6.25 kHz spacing.

12.5 kHz spacing is going to DOUBLE the number of available channels. Why would they ever need more? For the most part, the railroads do fine with ~90 channels.

Some metro areas have a few problems. Not even big ones... When you get several railroads with several yards each in the same area, and each yard uses one, two or twelve frequencies, 99 frequencies gets eaten up fast.

 

[seligman]

Some metro areas have a few problems. Not even big ones... When you get several railroads with several yards each in the same area, and each yard uses one, two or twelve frequencies, 99 frequencies gets eaten up fast.

This is a problem in a handful of areas, but that's it. It's exaggerated by railroads licensing frequencies they rarely, or never use. Doubling the number of channels with 12.5 kHz spacing should be more than adequate.

 

[burner50]

This is a problem in a handful of areas, but that's it. It's exaggerated by railroads licensing frequencies they rarely, or never use. Doubling the number of channels with 12.5 kHz spacing should be more than adequate.

I understand that it is only a problem in a handful of areas, I was pointing out that there can never be too many available frequencies.

 

[KMA367]

A bit off-topic - TV Ch 15

I just read the LA county is not going to it [700 MHz] and has requested the entire TV channel 15 (ala NYC and channel 16). The coordinators need to be made to understand that they are only recomenders, not gods. I was licensing channels before coordinators existed, and you think they are bad, you should have had to deal with the FCC directly back then.

L.A. County's request for all of TV Channel 15 for public safety has been approved by the FCC:
http://www.fcc.gov/Daily_Releases/Daily_Business/2008/db1230/DA-08-2823A1.pdf was the "preview," and Weekly SoCal FCC Grants contains link to all the freqs/licenses.

L.A. area Public Safety already has all of TV channel 16, and sizable portions of channels 14 and 20. UHF will be the voice band for the proposed countywide system (if it comes to fruition), and data will use 800 Mhz and possibly some of 700 MHz.

 

[AK9R]

Doubling the number of channels with 12.5 kHz spacing should be more than adequate.

The current channel spacing in the VHF rail band is 15kHz. The future spacing is 7.5kHz. 12.5kHz spacing only applies to bands where 25kHz was the standard channel spacing, such as UHF and 800.

Be careful to not confuse channel spacing with channel bandwidth.

 

[radioman2001]

I totally agree, that's what I believe is the problem,I have been having with the coordinator as far spacing and bandwidth. A more direct answer should be what emissions are allowed on these 7.5 kc spaced channels. I have seen other RR's licensed for 11k6F3E, which should translate out to 11.3kc bandwidth, F=FM, 3=Analog and E=Voice. Will my HT-1250 and CDM-1250 radios do this bandwidth. The Choices are 20kc, 25kc, and12.5kc. Also what emissions do the FCC allow for these channels. I have been looking over the FCC database looking for a link to frequencies and allowable emissions. Any help would be appreciated.

 

[N_Jay]

11k6F3E is commonly called 12,5 kHz

 

[radioman2001]

That may be part of the problem I am having with a non-technical coordinator. Now do the current HT-1250 and CDM-1250 series of radios meet that emission? I think I answered my own question. Thanks for the reply.

 

[bruch]

Take a look at FCC Part 90.207 and 90.209 (5) note 3. It's not totally the deviation but the emission of the radio that designates it's bandwidth, 6.25 NXDN is 4K00F1W, where 12.5 analog is 11K2F3E or 8k30F1E, and would occupy more bandwidth than allowed at 6.25 (6K00) with 2.5 khz of deviation. The radios emission type is usually found on it's spec sheet. No one that I'm aware of is currently making or trying to make an analog 6.25 because it looks impractical.

73's
Bob