What I meant to write was, "For non-commercial VFR in the UK, if communication is required, the equipment requirement is for only one COM radio."

So, have I got this right, I can leave the 25 spacing radio in and use it as long as my route doesn't require me to use 8.33, at least until september?

Depends on how you define "to use 8,33". The one case where you could theoretically get in trouble is when you use the "old" radio on a new "frequency" of which a neighbour frequency is in active use; you could then disturb communications there and that might perhaps be traceable to you and then you might be invited for tea with no biscuits.

Example: published frequency = 118,005, you tune in with your 25 kHz radio set to 118,000. Perfect communications however you are also transmitting into the 118,020 (or was it 118,015?)channel (we shouldn't speak of frequencies any more, to be correct, but rather of channels).

I do not think there are many cases yet of adjacent channels being in use, but have no references.

When I picked up the mighty Airtourer from Elstree after she had her new Trig 8.33 and Mode S fitted I had an interesting chat with the gentleman in the tower. Apparently since they went 8.33 they are getting a lot of interference from French radio which they never had before........ wasn't 8.33 supposed to stop this? Doh, EU Against Sensible Aviation strikes again!!

LowNSlow, Elstree haven't changed their frequency from 122.4, have they?

Elstree is definitely not 8.33 yet and I can't believe anyone in the tower would have said it is. The change over is due at the end of this summer.

For many decades we've had clear reception of French aircraft (transmitting in French) during certain weather conditions on 122.40. It's possible the controller who said that is fairly new to Elstree.

Particularly during stable, anticyclonic conditions, 'Sporadic E' can cause refraction of VHF signals so that they are heard well outside the intended area of coverage. We used to get a lot of French aeronautical VHF at Brize on one of the normal approach frequencies.

On my drive to AeroExpo last year, French VHF-FM was coming in loud and clear over my car radio! Back in 1967, our school CCF used the '88 set' ex-army radio, which worked on 4 frequencies at around 40 MHz. Because Channel B (41.4 MHz) was close to the BBC TV 405-line Channel 1 signal on 41.5 MHz, a rivet had been installed in the channel selector, giving access only to Channels C&D. On the day of a CCF Field Day, sporadic E was so predominant that Channel C was completely blocked by foreign TV sound, leaving us with only one channel to use.

As the '88 set' pre-dated BBC-TV in many parts of the country, complaints about 'army interference' steadily mounted in the 1950s-60s as the '88 set' began to replace the ancient HF '38 set' at CCFs, leading to the blocking of Channels A&B - and it was very difficult to remove the rivet :\!

ShyTorque, nope, it is still 122.4 which puzzled me when the chap mentioned the 8.33. Mr Average, I think he is quite new as I don't recall seeing him there before although I don't visit as regularly as I used to.

AIP Supplement 009/2018 lists the stations that have converted and those due to convert within the next 60 days. Elstree is not listed.

Short version:

You can use your 25kHz radio on any remaining 25kHz frequencies during 2018, but only until they change to 8.33kHz channels, which you can’t use it on. After 01/01/19 it is dead weight, as all frequencies should be 8.33kHz channels by then.

Except they won't!
The following assignments will remain on 25 kHz permanently:

• 121.500 Emergency Frequency.
• 123.100 SAR Auxiliary Frequency.
• 122.100 NATO Combined Frequency.
• The VHF digital link frequencies 136,725 MHz, 136,775 MHz, 136,825 MHz, 136,875 MHz, 136,925 MHz and 136,975 MHz.
• The ACARS frequencies 131,525 MHz, 131,725 MHz and 131,825 MHz.
• Where offset carrier operation within a 25 kHz channel spacing is utilised (e.g. VOLMET).

25kHz channels are also 8.33kHz channels. Are you saying that those channels won't be used????

They will be used - actually some are being used now - but under another name and with less bandwidth.

Actually 121.5 still uses 100 kHz frequency spacing. It was not affected in the earlier splits from 100 kHz to 50 kHz to 25 kHz, and it's again not affected now.

https://en.wikipedia.org/wiki/Airband

What about SafetyCom on 135.475?

How does that work, since the bandwidth of an AM signal is +/- the highest modulating frequency, which is about 3kHz? Or is it just more selective filters in the receiver?

Mainly narrower filters in the transmitter section. As I stated before: if one transmits on, say, 119,000 Mhz with a 25 KHz filter than one will also be received/heard on 119,0 - 8,33 and 119,0 + 8,33 - which is not what is intended.

But also narrower band filters on the receiving side, for the exact same reason, mutadis mutandis.

Are you sure? The bandwidth of the transmitted signal is about 6kHz and a reasonably modern 25kHz radio would not interfere with the adjacent .833 channels.

Good try! There are two slightly different things here. The permitted bandwidth of the transmission and the fact that 121.500 is protected by a guard band that can vary by region of the world. The The requirements are laid down in ICAO rules. The bandwith is 25 kHz but the frequency is protected by a guard band that is wider.

The European situation regarding bandwidth is in regulation 1079/2012 where it states 25 kHz channel spacing.

It says in "Amendments to Annex 10, Volume V, Chapter 4" of Oct 2011
4.1.1.1 The block allotment of the frequency band 117.975 – 137 MHz shall be as shown in Table 4-1.
b) 121.5
Emergency frequency
In order to provide a guard band for the protection of the aeronautical emergency frequency, the nearest assignable frequencies on either side of 121.5 MHz are 121.4 MHz and 121.6 MHz, except that by regional agreement it may be decided that the nearest assignable frequencies are 121.3 MHz and 121.7 MHz.

4.1.3.1.6 The emergency channel (121.5 MHz) shall be available only with the characteristics as contained in Annex 10, Volume III, Part II, Chapter 2 for equipment with 25 kHz channel spacing.

COMMISSION IMPLEMENTING REGULATION (EU) No 1079/2012 of 16 November 2012

Article 2
4. The conversion requirements shall not apply to frequency assignments:
(a) that will remain in 25 kHz channel spacing on the following frequencies:
(i) the emergency frequency (121,5 MHz);

No, they are 25kHz frequencies, not channels.

If someone wished to retain a 25kHz set purely on the offchance they needed to call 121.5, or their presence is required on NATO Common, that’s up to them I suppose. But they’ll need an 8.33 kHz set for anything else after 01/01/19.