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Author Topic: 2m VHF band to be surrendered to aviation?  (Read 18047 times)

Offline Looking-Glass

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2m VHF band to be surrendered to aviation?
« on: July 24, 2019, 1640 UTC »
There has been a lot of discussion in the past three weeks about suggestions that the 2m amateur radio VHF band could be given to the aviation sector.

Mainly Europe being mentioned and also a hint that Asia/Pacific could follow through with same proposal.

With a huge increase in world wide aero traffic the current band from 118-137MHz is under stress from traffic overload and pressure is mounting to expand into a new frequency block (ie: 2m amateur radio band) to ease channel congestion and enhance communications safety.

I often listen to Brisbane Centre here in Australia on 119.700MHz and Melbourne Centre on 129.800MHz and in morning and afternoon peak flight arrival/departure times the ATC is literally working one aircraft after another on this sector, often aircraft can be heard doubling together calling the ATC centres.

So something has to be done to ease congestion on the 25KHz spacing allocation currently under stress.

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Offline R4002

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Re: 2m VHF band to be surrendered to aviation?
« Reply #1 on: July 26, 2019, 1241 UTC »
Europe switched to the 8.33 kHz spacing a bit ago now.  I don't really understand why they picked 8.33 kHz.  They could have done 12.5 kHz (increase 760 channels to 1520 channels) but instead they divided 25 kHz by 3 to get 8.33 kHz channeling, for 2280 channels.  Of course, this causes all sorts of weird rounding off of the frequencies when read over the air.  They would have been better off with doing 5 kHz spacing at this point (since most frequencies are apparently rounded off to the nearest 1xx.xx0 or 1xx.xx5 frequency when read over the air.  I know the AM emission is 6K00A3E (so 6 kHz bandwidth).   

But, instead, they did 8.33 kHz for Europe.  I know most the of the rest of the world still does 25 kHz spacing for VHF airband.  Expanding the band from 136.975 MHz (or is it 136.98333 MHz, rounded up to 136.985 MHz...or 136.99166 MHz, rounded down to 136.990 MHz???  We'll say 137.000 MHz for the sake of simplicity - 137 MHz to 144 MHz that's an additional 7 MHz of spectrum (to be shared with satcom and other users...the same issue with sharing it with 2-meters, or "sharing" it with 2 meters, I should say). 

Expanding the band from 136.975 MHz up to 144.000 MHz (or 143.975 MHz) at 25 kHz channel spacing (or 40 channels per MHz) would give an additional 280 channels, or 279 channels.  8.33 kHz spacing gives 120 channels per MHz, so that would be an additional 839 channels or 840 channels, depending on how big of a guard band you want before you get to 144.000 MHz. 

The United States military makes extensive use of 137-144 MHz and 148-150.8 MHz for air-to-air communications as well as military land mobile comms and other things, including VHF SATCOM purposes and other niche uses.  Military air-to-air use AM mode with 25 kHz channel spacing while land mobile and other purposes use 12.5 kHz channel spacing and FM voice, Project 25 digital voice or other digital modes. 

The VHF air band was originally (back in WWII) 100 MHz to 156 MHz with weird spacing, maybe 40 kHz channels?  Then it was changed to 108 MHz to 132 MHz, then 135 MHz, then 136 MHz, then 136.975 MHz (if my memory serves me correctly)...with channel spacing getting progressively smaller (100 kHz, then 50 kHz, then 25 kHz...).   Because of the original 100-156 MHz VHF-AM band, the US military has continued to include the band above 137 MHz in its VHF air radios.  Most of them do 108.000 MHz - 151.975 MHz I believe, including the 2 meter portion 144-148 MHz. 

The 2 meter band is one of the busiest amateur bands in VHF/UHF, if not the busiest, at least in the USA.  I know in a lot of places its 144-146 MHz and not 144-148 MHz.  There are plenty of users of the 137-144 MHz region and 148-150.775 MHz region (in the USA, once you get to 150.775 MHz, you get into the Part 90 land mobile radio services, with 7.5 kHz steps). 
The whole bandwidth is bigger than channel spacing seems to work with the VHF and UHF land mobile narrowbanding completed back in 2013.  12 kHz wide signals on 7.5 kHz channels.  Of course systems aren't supposed to be put right next to each other in frequency, but in practice they are.  In my local area, for example, each local public school has its own VHF repeater.  They're low power on-site repeaters (anywhere from 10 watts to 50 watts output power) but they actually carry quite a distance.  These repeaters are literally right next to each other in the band plan (152.9000 MHz, then 152.9075 MHz, or 152.3900 MHz, then 152.3975 MHz, then 152.4050 MHz, then 152.4125 MHz, then 152.4200 MHz, then 152.4275 MHz, literally every channel step has an active repeater on it, some of them having more than one.  152.3000 MHz is used by two different schools, a local taxicab company and a local quarry...and the adjacent frequencies 152.2925 MHz and 152.3075 MHz are also both active. It's done by putting the adjacent-channel repeater as far away as possible and using CTCSS and DCS tone squelch systems.  I know that's not possible with AM voice on the air band, of course.  With FM you also have the advantage of the capture effect, whereas multiple AM signals just mix with each other on the receiver. 

The local National Guard uses a portable Project 25 digital system (portable system) with several frequencies between 148.000 MHz and 150.800 MHz used - including 150.800 MHz itself, even though that's technically allocated for land mobile, 150.775 MHz, 150.7825 MHz, 150.790 MHz, 150.7975 MHz, 150.805 MHz, 150.8125 MHz, etc etc.  There are some special rules for 150.775 MHz and 150.790 MHz given the fact that they're in the "boundary area" between military AM aircraft and FM/P25 voice band and the beginning of the FCC allocated land mobile VHF band.   Like most things, the military can use the frequencies they want/need even if those frequencies fall within the civilian land mobile bands...provided there isn't a major interference issue.  This is also the case in the 30-50 MHz region...but I digress. 

Since aircraft radio communications are certainly what I would consider "safety of life" communications...I don't know if a "secondary" allocation is really possible in the real world.  Maybe increase the band from 137 MHz up to 144 MHz?  These frequencies aren't empty, and neither is 144-146 MHz / 144-148 MHz.  I don't like it. 
U.S. East Coast, various HF/VHF/UHF radios/transceivers/scanners/receivers - land mobile system operator - focus on VHF/UHF and 11m

Offline Josh

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Re: 2m VHF band to be surrendered to aviation?
« Reply #2 on: July 26, 2019, 1936 UTC »
I can see it either way, I mean it's not like they didn't take part of 220 from us and then it goes unused.
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