8.33..? 25.0 still allowed.

[scifi]

Just read the UKGA announcement that because of limited amount of Avionics Fitters, 25 KHz Radios will still be allowed... As long as you don't contact anyone on the new 8.33 frequencies... Don't think they have thought that one out... My 25khz rig never did 8.33 anyway !
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[Heston]

Er I think you will find that over the next few months (and certainly by end of 2018) there will be almost no 25khz frequencies left for you to talk to!

[Sam Rutherford]

As I understand it, the 25KHz units can still "communicate" with the nearest 8.33KHz frequency - if a little crackly?

[BEagle]

The third call period for CAA funding for 8.33 kHz compliant radio equipage is now open and will run to 31 December 2017. Don’t delay any applications!

UK adoption of 8.33 kHz VCS capable equipment is increasing and feedback shows that over 50% of the UK GA fleet is already equipped. But the CAA has recently become aware of aircraft equipage issues regarding the limited availability of installers. Hence a number of limited time frequency exemptions have been invoked, to provide flexibility for users and to help with the capacity issues that have been identified. The exemptions will run to 31 December 2018 and are listed in CAP 1606. See http://publicapps.caa.co.uk/docs/33/CAP%201606%20833%20Limited%20Time%20Exemptions.pdf

Note that 8.33 kHz compatible radios are backwards compatible, so will retain the capability to communicate with existing 25 kHz ground stations before those ground stations have been converted. When a '25kHz' frequency is selected, the receiver filter and transmitter characteristics of an 8.33 kHz radio are automatically adjusted to cater for 'offset carrier' operation, so there is no need for the user to make any other selections.

Existing 25kHz radios may be left installed provided that the transmitter function is only used on exempted frequencies.

[ChickenHouse]

From the sheeps field to the warm coffee round the corner you may get around on 25, but also as NORDO. If you travel in the EU, you have no chance to avoid 833 but for quite some month already.

[this is my username]

Lots of a/g radio stations will be changing to 8.33 frequencies soon (eg Old Sarum is now 123.205). You will still be able to speak to them with your 25kHz set, but it won't be legal.

[Andy H]

I've just found CAP 1606 that lists the 25kHz frequencies that will remain in use. Safetycom is one of them

[ChickenHouse]

Lots of a/g radio stations will be changing to 8.33 frequencies soon (eg Old Sarum is now 123.205). You will still be able to speak to them with your 25kHz set, but it won't be legal.

And do not forget - if you have mixed communication between a radio on '833 and another on '25 you will have a more unstable link due to the different power filtering.

[VQ5X03]

A 25kHz bandwidth receiver will have the capability of receiving 3 x 8.3k-spaced transmitters when tuned to a 25k spaced channel. Deciding which one was for you could be a potential issue.

The audio filtering on a 25k bandwidth radio's transmission would *probably* limit the transmission width to be within an 8.3k radio's receiver bandwidth if they were both on the same 25k-spaced centre frequency. If not, the adjacent 8.3k channel receivers, if reasonably close by, would hear 'splatter' from the higher audio frequencies.

It would be nice to think that adjacent 8.3k channels are going to geographically very widely spaced...?

[ChickenHouse]

Width and selectivity is one point, power and receiption another. When a 25 TX, up to 2/3 of the power may be outside of the 833 RX.

[VQ5X03]

When a 25 TX, up to 2/3 of the power may be outside of the 833 RX.

Agreed if the audio filtering on the 25kHz-spaced Tx is very wide. I don't have any specs for modern 25kHz airband transceivers but I would think the audio bandpass drops off rapidly after 3 or 3.4kHz, so the max power in a 25k (AM) transmission sidebands would be only 6 or maybe 7kHz wide... Happy to be corrected!

[scifi]

I really wonder why they have increased the number of channels by x3, will that mean there will be 3 times more ATC Jobs going in the future.?

Or will it just mean that each airfield will have its own unique frequency.
At 3000ft overhead our airfield we sometimes hear another airfield's radio chatter, when that airfield is across the width of the country from ours.

[ChickenHouse]

I really wonder why they have increased the number of channels by x3, will that mean there will be 3 times more ATC Jobs going in the future.?

Or will it just mean that each airfield will have its own unique frequency.
At 3000ft overhead our airfield we sometimes hear another airfield's radio chatter, when that airfield is across the width of the country from ours.

Rumors I heard were it was due to the incompetence to arrange EU-wide frequencies, so each country did its own without coordination. Second may be the increasing power of modern radios, as in the old days of 5-6 watts it was easy to be far away, but at 10-16 watts far is much farther. I somehow doubt they really needed it, especially looking at airspaces like in the US still running fine on 25.

[Johnm]

Rumors I heard were it was due to the incompetence to arrange EU-wide frequencies, so each country did its own without coordination. Second may be the increasing power of modern radios, as in the old days of 5-6 watts it was easy to be far away, but at 10-16 watts far is much farther. I somehow doubt they really needed it, especially looking at airspaces like in the US still running fine on 25.

The problem is that we haven’t been able to get an effective European mechanism for frequency allocation. The EU only gets to organise stuff the member nations sign up to under the Treaties and thus far there hasn’t been an appetite for common action.

[ChickenHouse]

Does anybody have a link to the UK-8.33-roadmap? I was flying to Old Sarum lately and they already changed to a 8.33 frequency.

[scifi]

I think the roadmap will be an ongoing item, as more airfields decide to want a unique frequency. For us GA types, (doing General 'Andling,) we would hope not to hear any other transmissions from over 60 miles away. It is probably much worse for the airlines, traveling at FL400, they would not want any other transmissions from over 300miles away.


I listened to the whole of the last flight of Concorde, from Manchester to London. From N Wales I could hear them ask for supersonic above the Severn Estuary, then heard them turn above the Bay of Biscay. I only lost them when they were below 4000 ft on approach to LHR. and of course I cold not hear LHR Tower.
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