The current forum software loses track of post numbers if posts have been moved, threads merged, etc. This is normally not an issue (the sequence is not lost) but it makes it difficult to obtain a URL to such a post. I did merge some 8.33 threads, etc.
FWIW, I almost never delete posts. Well, I delete the following
Yes, but to what purpose does it serve? Within a couple of years all will be 8.33 and we are left with two frequencies (channels) with the same frequency. I just don’t get it.
It is for the decade of transition.
Over time, slowly but steadily, one 25 kHz frequency gets replaced by three 8.33 kHz frequencies. From a pilot’s point of view, it is as simple as it gets – get told a magic number, and dial magic number in the radio.
Eurocontrol used this first in upper airspace, and then slowly and surely this has been percolating down into other airspace, and it will finally be universal. Doing it in upper airspace was quite clever, too – these frequencies have a HUGE protected area, to add a single 25 kHz frequency to upper airspace you would have to retire that frequency at many other stations with smaller coverage. If you do that you might as well create three 8.33 frequencies.
We can argue until the cows come home whether it is necessary, but as soon as operationally important frequencies move to 8.33, you need to have a radio that can use these, and eventually a 25 kHz radio becomes useless except for emergencies.
The only real issues are:
As usual, it’s not the Engineers, but the Bureaucrats that create a mess.
Cobalt wrote:
It is for the decade of transition.
Actually it will be much, much more than a decade. Sure, the EU announced the transition to 8.33 in lower airspace in 2007, to be in effect by the end of 2017, but the transition already started a lot earlier. The earliest date I found was 1999, for FL245 and up.
But it’s also a lot more at the back end. Like I said earlier, certain frequencies will not be converted to an 8.33 frequency and will, in some cases, even remain a 100 kHz separated frequency (like 121.5). But also non-EU places like the US may not start the transition to 8.33 anytime soon, if ever. As aviation is by its very nature very international, this will mean that your radio will have to be able to deal with 100 kHz, 25 kHz and 8.33 kHz separated frequencies well past 2017.
Until, at some point in time, we may have to switch radios again, to go to some sort of digital radio system which may use a different frequency band altogether. Which, by the way, may also require a new antenna and wiring. And since the frequencies might not be in the usual VHF MHz range, will require some new phraseology. And maybe a new interface to your radio to set the “channel” or whatever it’s going to be called. And who knows, we might just follow the maritime world and introduce duplex channels. Which brings in a whole new dimension of their own – especially when out of reach of the ground station who can repeat the ship-shore signal onto the shore-ship frequency.
LeSving wrote:
I still don’t get it. You can switch to “25.0 mode” for those areas.
Sure, but you make the user interface considerably simpler and less prone to error if all you have to show on a chart, or pass in a message, is a single number – and all the pilot needs to do is turn a knob till the display shows this number – job done. Add extra knobs and information so you have to select the right mode for the area you fly in, and mistakes will be made, and it’s unneeded complexity on the user interface which the pilot would have to deal with (who in most cases knows nothing about how radios work).
User interface design is pretty important to get right and make as intuitive as possible.
LeSving wrote:
This is the kind of thing that only the EU bureaucracy could invent
It was unlikely to have been the EU who came up with this, given that it’s a world standard – more likely a world body like the ITU.
Thought I’d try this. Switching the 430 is trivially easy – Aux, 4 clicks of the small knob, and there it is!
So I tried adjacent channels, on the ground, 50 yds from the tower. One up = perfectly clear, normal communication, slightly hollow sounding. One down, unreadable, buried in mush. So on that scientific test, a) the 430 ‘Comms Mode’ selection does do something b) the lower channel would not offer crosstalk at any practical range, the higher channel is still unproven but would probably vanish at any range.
The tower radio is still 25Khz.
The 430 will stay on 8.33 from now on.
So does any onw know of a "slide in " replacement for the good old King KX155 radios?
25khz ‘channels’ are going to be with us for some time for the many ground stations which operate multiple simultaneous transmitters using the offset carrier method of operation also known as Climax. Extract from UK CAA doc below:
2. Within the United Kingdom, virtually all VHF RTF channels provided for en-route air traffic control and those used for emergency, flight information services and VOLMET are operated from between two and four radio stations using the off-set carrier technique in accordance with the standards set down in ICAO Annex 10. The off-sets employed are; ± 5 kHz for a two station system, ± 7.5 kHz and 0Hz for a three station system and ± 7.5 kHz and ± 2.5 kHz for a four station system.
3. When an aircraft is operating within the range of two or more stations, the individual transmissions combine in the airborne receiver to cause one or more audio heterodynes having a minimum frequency of approximately 5 kHz. These heterodynes appear above the normal audio pass-band of the receiver and are not heard by the flight crew.Interesting. Can they do the same thing within the bandwidth of an 8.33 channel? Offsets for a four-station channel would need to be something like +/- 2.5 kHz and +/- 0.83 kHz, leading to a 1.67 kHz heterodyne. Would that be cut off by the filter as well? I seem to remember that the human ear has an audible range from something like 0.5 kHz to 4 kHz so 1.67 kHz would be right in the middle of that.
