BackPacker wrote:
"...but then you are interfering with 120.590 and 120.610.
In all fairness, those frequencies are probably not in use yet. But you have no idea if and when they will be. So not good practice to mix 25 kHz and 8.33 kHz frequencies. And most likely illegal anyway."
I understand the point about the interference (and have an 8.33kHz handheld anyway) but almost certain that the adjacent frequencies are not allocated in the UK because the law does not change until next year. From the CAA website:
"On 1 January 2018 the law changes and all aircraft operating in airspace that requires the carriage of a radio must have 8.33 kHz-compatible equipment fitted and operational. After this date all 25kHz radios can no longer be used, unless specifically exempted for a particular channel such as the emergency frequency 121.5MHz. This means that all General Aviation (GA) aircraft must comply with this change to UK law to maintain safe communications with ground stations.
The UK leaving the EU will not affect the implementation of this new legislation."