8.33 spacing

[pauldenisowski]

If anyone would like a brief overview of 8.33 kHz channel spacing (and how it's different from 25 kHz), I just posted a video on this topic

 

[Scan125]

I'll chip in here.

UK/EU certified aircraft radio kit will handle 25kHz and 8.33kHz perfectly.

In the case of 25kH spacings/steps then the dialled frequency (I prefer "setting" as it is from the pilots point of view just a setting value) will be an actual 25kHz value.

In the case of 8.33kHz then the cockpit "setting" is just a setting and not a frequency.

All of this is just attempts and trials to get around serious frequency congestion issues in the European Air Space.

I doubt it was done on a random will but a current crammed issue and the expectations that things will get worse.

Also the authorities would have done extensive technical research into old and existing certified radio kit on their "selectivity" capability. By that they could have split 25 into 12.5kHz chunks. No doubt they found that kit could resolve and separate 8.3kHx (8.3333333333) so now 25 becomes 8.33333 times 3 = 25.

I'm not even going to say I like the munging (munging) of this previously 25 defined spacing but it is what it is.

Some scanners get the 8.33 spacing correct. Some partially correct and no doubt manually entered "setting" on a pure frequency orientated bit of kit will not be on the correct frequency.

 

[Ubbe]

Some scanners get the 8.33 spacing correct. Some partially correct and no doubt manually entered "setting" on a pure frequency orientated bit of kit will not be on the correct frequency.

Those scanners that doesn't set their frequency exactly to 8.333 spacing are probably using 12,5KHz wide filters or even wider as in Unidens conventional scanners, so that it will be a huge margin to still receive transmissions with full audio quality.

/Ubbe

 

[Scan125]

Those scanners that doesn't set their frequency exactly to 8.333 spacing are probably using 12,5KHz wide filters or even wider as in Unidens conventional scanners, so that it will be a huge margin to still receive transmissions with full audio quality.

/Ubbe

Probably but for example the UBC125XLT and possibly the BC125AT get some wright and some wrong.

e.g. see here: Scan125 Control Program User Manual

In contrast the 75XLT gets all the freqs. correct:

Scan75 User Manual

I don't think as such 12.5kHz has anything to do with it. There is a clear defined mapping to cater for 8.33kHz and it seems that some scanners in their civil Airband range get the mapping wrong.

 

[bearcatrp]

Seems weird the 160DN has the airband set at 8.33 spacing program In the menu. Thought that was odd for a USA version.

 

[Ubbe]

I don't think as such 12.5kHz has anything to do with it. There is a clear defined mapping to cater for 8.33kHz and it seems that some scanners in their civil Airband range get the mapping wrong.

It perhaps are dependent of what PLL chip that are used, what its prescaler are capable of and perhaps it can only handle down to 3.125KHz steps and will then be 1KHz off, something that many scanners are off from the factory. My BCD536 are off by 1KHz and my TRX-2 are 1KHz off in the other direction.

/Ubbe

 

[Scan125]

It perhaps are dependent of what PLL chip that are used, what its prescaler are capable of and perhaps it can only handle down to 3.125KHz steps and will then be 1KHz off, something that many scanners are off from the factory. My BCD536 are off by 1KHz and my TRX-2 are 1KHz off in the other direction.

/Ubbe

I'm not sure that this is applicable. What happens is that ATC calls 118.030, one enters 118.030 and the REAL frequency is 118.0250 but the scanners sets 118.0333.

I'll be open here as well because it is some time since I dug into this 8.33 saga. All I do know is that my program has what I call air-band correction to correct the scanner errors.

Of course with a true/certified air-band radio/transceiver is that for you ATC say 123.4567 this is what you enter and your radio will display 123.4567. However the actual frequency use could be completely different. Pilots, ATC don't care. As far as they are concerned it is 123.4567.

 

[prcguy]

I'm not sure that this is applicable. What happens is that ATC calls 118.030, one enters 118.030 and the REAL frequency is 118.0250 but the scanners sets 118.0333.

I'll be open here as well because it is some time since I dug into this 8.33 saga. All I do know is that my program has what I call air-band correction to correct the scanner errors.

Of course with a true/certified air-band radio/transceiver is that for you ATC say 123.4567 this is what you enter and your radio will display 123.4567. However the actual frequency use could be completely different. Pilots, ATC don't care. As far as they are concerned it is 123.4567.

I’m happy the US has not migrated to 8.33, what a big hassle.

 

[Scan125]

I’m happy the US has not migrated to 8.33, what a big hassle.

I'm with you on this BUT it may come your way at some point in time. Europe had to divide the 25kHz into narrower spacing as their air-band comms are so congested. To add to the congestion many airports like London, Manchester, Paris, etc. are all within comms range of each other. Whereas in the US New York is well out of range of Las Vegas so no air-band overlap.

One could redesign the whole air-band comms system world wide, as opposed to the likes of the 8.33 hack, but the expense etc for every commercial and private aircraft, airport, airfield etc. would be immense and cause massive disruption etc.

A solution, which might also be more secure and always available is to progressively switch to satellite (or similar) leaving the existing system in in place but less used. The current VHF system would join the HF system as alternatives when required.

 

[Ubbe]

I'm not sure that this is applicable. What happens is that ATC calls 118.030, one enters 118.030 and the REAL frequency is 118.0250 but the scanners sets 118.0333.

If you enter a 118.030 frequency manually the scanner will pick the closest valid frequency which is 118.0333 and will display and use that frequency. If you are searching a band it will first stop on 118.025, the correct frequency. If you program or enter a frequency manually then you'll have to know what the real frequency should be if you have set a 8.333 channel step.

Luckily I have none of those 8.333 channels in use over Scandinavia and are probably only a thing over central Europe and then only in the higher part of the VHF airband. I have no idea why they choose to rename all 25KHz channels so that 118.025 are called 118.030 and 118.100 are called 118.105

/Ubbe

 

[Scan125]

If you enter a 118.030 frequency manually the scanner will pick the closest valid frequency which is 118.0333 and will display and use that frequency. If you are

Well this is the problem with some scanners on air-band frequencies. With correct 8.33 handling then the scanner when 118.030 is entered it should tune to 118.0250 and not the next step value. So at a minimum I expect the scanner to tune to 118.0250 and not 118.0333. Ideally having tuned to 118.0250 it should display 118.0300 which is what a pucker air-band receiver/transceiver does.

searching a band it will first stop on 118.025, the correct frequency. If you program or enter a frequency manually then you'll have to know what the real frequency should be if you have set a 8.333 channel step.

Luckily I have none of those 8.333 channels in use over Scandinavia and are probably only a thing over central Europe and then only in the higher part of the VHF airband. I have no idea why they choose to rename all 25KHz channels so that 118.025 are called 118.030 and 118.100 are called 118.105

/Ubbe

All transatlantic aircraft have to be able to handle the 8.33 correctly. I suspect that this also applies to all military aircraft in the US / elsewhere as they may be deployed to the EU region.

In the traditional CB bands all the kit dial and show channels and not frequencies. However CB came long after air-band VHF and the concept of channels made sense in terms of generally usability for the less technically inclined persons. Save goes for Marine, all channel defined and not frequency defined.

Like you say 8.33 is a horrible mess / concept but they had to get more into the otherwise wide 25kHz space. I guess they could have chosen (as suggested) 12.5 which would have worked out quite nicely but I presume they looked into the future expected growth of traffic and decided that as the existing radios can discriminate to 8.33 without problems and leave a sufficient guard band to stop cross channel interference then getting from 1 'channel' per 25kHz to 3 compared to 2 then 3 per 25kHz made sense. That just left them with the problem of how to tune in 8.33 steps when the radio kit did not have enough thumb wheel dial resolution to enter an 8.33 value. Solution - frig it on the thumb wheels and ATC calls to dial a 6 digit number instead.

 

[JensLK]

I will never understand why anyone would scan an air band. When I listen to air traffic radio, I have a specific purpose in mind. So I set the scanner to the well-known frequencies and listen. When a handover is made to another station that I don't know yet, the frequency is announced by ATC and I save it. If I hear someone talking somewhere on the airband and don't know who they're talking to, it makes no sense except that it sounds funny. Right?
And for programming ATC frequencies to memories no modern scanner has a problem with 8.33Khz spacing.

 

[Ubbe]

I will never understand why anyone would scan an air band.

There's unlisted frequencies in use that you will have to search for to find. There's a flight path from USA and UK that goes right above Stockholm at 30.000 feet on their way to Russia, India and Japan where they talk between airplanes about mostly private matter what they do at home and what they earn at the other company they moved to and if they need more staff and so on, and its'not at 123.45MHz.

There's also a non-listed frequency used maybe 2-3 times a year where a special calibration aircraft, that I think is stationed in Germany, goes from airport to airport in different countries and measure the airports ILS systems and beacons and have constant communication with the ground based crew. They usually measure during one full day and then makes adjustments to the ground transmitters and verify the changes the next day. Maybe not interesting to the average Joe but to any technically interested guy it is pretty exciting to listen to and how they have to keep out of the way of normal aircraft traffic but still needs to measure at the exact same glide path that those airplanes are using.

I have one or more scanners doing constant searches, not only in the aircraft frequency bands, for any unknown frequencies in use.

The FCC department in my country have no public database where anyone can look up on a frequency. You'll have to make a phone call or send an email to request info about a frequency, or ask about what licenses that exists in a frequency range in a geographical area. And to discourage people from doing requests they sometimes say they'll need all your info, like social security number to look up the history if you have been involved in any crime, and they sometimes send a reply by postal mail and sometimes you will have to sign to get the letter and both postage and the special service for signing as well as a service charge for each page they have printed are a cost you will have to pay.

And the thing is that when someone applies for a frequency license they can tick a box that says that they do not want their info to be publicly available. When we then request info we are told that there's isn't any info available. Se we will have to do our own searches to get aware of what transmitter sites there are out there, besides taxi, road works and package delivery services.

/Ubbe

 

[Scan125]

I will never understand why anyone would scan an air band. When I listen to air traffic radio, I have a specific purpose in mind. So I set the scanner to the well-known frequencies and listen. When a handover is made to another station that I don't know yet, the frequency is announced by ATC and I save it. If I hear someone talking somewhere on the airband and don't know who they're talking to, it makes no sense except that it sounds funny. Right?
And for programming ATC frequencies to memories no modern scanner has a problem with 8.33Khz spacing.

I think the point is that the ATC called frequency IS NOT necessarily the ACTUAL RF frequency used. This also goes for airport published so called frequencies. They are just (when it comes to some 8.33 based stuff) just numbers to dial into your aircrafts radio kit. If you just scan by frequency then you will no doubt hit an ATC real live frequency. No issues with 25kHz based freqs as these will match the ATC called freq. Other frequencies may be 8.33 based and will not match the called ATC "setting". Note setting and not frequency!

This is why some people now refer to ATC settings as channels and no longer frequencies. The whole originally accepted norm is now completely screwed up. The only people who don't care is the ATC and pilots. If they had "A" or "B" settings that tuned to any old frequency they would not give a monkeys as long as someone was on the other end.

Scanners fundamentally work on frequencies. If you want to listen to CB channel 19 then you don't enter 19. You enter the actual frequency that channel 19 uses. This is where the problem with ATC arrives. People see hear abc.efg and bang that into their scanner only to find that for 8.33 based frequencies abc.efg is actually hij.jlmq and wonder why they hear nothing on abc.efg that they entered.

 

[Scan125]

There's unlisted frequencies in use that you will have to search for to find. There's a flight path from USA and UK that goes right above Stockholm at 30.000 feet on their way to Russia, India and Japan where they talk between airplanes about mostly private matter what they do at home and what they earn at the other company they moved to and if they need more staff and so on, and its'not at 123.45MHz.

There's also a non-listed frequency used maybe 2-3 times a year where a special calibration aircraft, that I think is stationed in Germany, goes from airport to airport in different countries and measure the airports ILS systems and beacons and have constant communication with the ground based crew. They usually measure during one full day and then makes adjustments to the ground transmitters and verify the changes the next day. Maybe not interesting to the average Joe but to any technically interested guy it is pretty exciting to listen to and how they have to keep out of the way of normal aircraft traffic but still needs to measure at the exact same glide path that those airplanes are using.

I have one or more scanners doing constant searches, not only in the aircraft frequency bands, for any unknown frequencies in use.

The FCC department in my country have no public database where anyone can look up on a frequency. You'll have to make a phone call or send an email to request info about a frequency, or ask about what licenses that exists in a frequency range in a geographical area. And to discourage people from doing requests they sometimes say they'll need all your info, like social security number to look up the history if you have been involved in any crime, and they sometimes send a reply by postal mail and sometimes you will have to sign to get the letter and both postage and the special service for signing as well as a service charge for each page they have printed are a cost you will have to pay.

And the thing is that when someone applies for a frequency license they can tick a box that says that they do not want their info to be publicly available. When we then request info we are told that there's isn't any info available. Se we will have to do our own searches to get aware of what transmitter sites there are out there, besides taxi, road works and package delivery services.

/Ubbe

Exactly with regards to private / unlisted frequency allocations. Also if you hit one of these freqs. then I'm fairly sure they don't use flight numbers/identifiers but some private company identification id/label and this is probably not the tailplane/aircraft international ID. After all these a private company comms not for general public identification or even ATC purposes.

 

[Ubbe]

I'm fairly sure they don't use flight numbers/identifiers

They just say "Charlie, are you there?" I have to look at the ADS-B data to see what aircrafts that are at 30,000ft to know who they are. Sometimes they talk japanese when two JAL aircrafts are going east with an hour between them.

/Ubbe