Timothy wrote:
That is demonstrably not true, in a real life scenario, as I have explained.
This might seem like nit-picking, but I don’t think it’s demonstrably untrue. All they can tell from the ground is that one radio isn’t as good as another. They can make an assumption you’re using a 25kHz radio, and in this instance they guessed right (assuming the 25kHz spacing radio is a modern one). As I said, you may find if you swap the feedlines on the two radios and transmit from the same place, they get readability 2 out of your 8.33 radio and in that case they will guess wrong that you’re using a 25kHz radio on 119.100 because the poor readability was not caused by the radio itself but by an issue with the antenna, feedline, radiation pattern etc.
Timothy wrote:
Firstly on a 25kHz box
What make and model was the box? And how old?
KX 155, unknown vintage (it was a student’s aircraft).
Peter said that no-one on the ground will know if you are using a 25kHz radio.
I did not say simply that; that would be disingenuous.
It is the 25k channels which became 8.33k by adding 5kHz to the real frequency, which can be used with a 25k radio and nobody can tell you are doing it. If one reads this thread, and the other one I linked, this becomes clear.
If the 25k radio is shagged and is way off on the carrier frequency, that’s a different argument completely – even though a lot of people seem to be flying with those.
Sorry, I misinterpreted
if you use a 25k radio nobody can tell
My bad.
Not sure if this is the right thread, but here goes…
Just as a heads-up to anyone planning a flight to Switzerland, most if not all the remaining frequencies in Switzerland changed to 8.33kHz on March 28, 2019. The primary impact is the AFIS frequencies for all the VFR airfields, and the changes are simply to add 0.005 to the previous frequency. So what were previously x.×00, x.×25, x.×50, x.×75 are now x.×05, x.×30, x.×55, and x.×80
The details were published very late, and didn’t make it into the 1904 cycle for Jepp in-panel system navdata or the VAC charts. At least my IFD still has the old frequencies. Since Garmin’s also use Jepp navdata, I assume the same for them. Perhaps someone can confirm. I’ve queried Jeppesen and they say the changes will be reflected in the 1905 cycle.
If ramp checked, are there any requirements to show proof of 8.33 capability?
My data point about using 25kHz setting for a 8.33 “frequency”.
8.33 is still not required for VFR in most of Copenhagen FIR, so GA aircraft radios are often left in 25kHz mode, which I had not bothered to check on the local IFR flight when I was first given a 833 “frequency”. I noticed it was .030 instead of .025, and because I saw the unit was in 25kHz mode, I just used tuned the old frequency. As expected this worked fine, ACC acknowledged that they read me 5/5, and I read them fine also. I have since done it deliberately a number of times without any problems.
But I take note that it may not work if trying to do the same with a 25kHz-only unit.
are there any requirements to show proof of 8.33 capability?
I believe this Q has come up before, with no known answer. IMHO the issue would be settled by an examination of the radio, which implies a really well briefed inspector, which implies it is hardly likely to happen unless you have drawn attention to yourself and p1ssed off somebody big 
There are stories of well briefed ramp checkers but rare; the only ones I recall are from France of police having checklists fo what should appear on an FAA license.
As expected this worked fine, ACC acknowledged that they read me 5/5, and I read them fine also. I have since done it deliberately a number of times without any problems.
But I take note that it may not work if trying to do the same with a 25kHz-only unit.
It all works perfectly. The transmission on 125.030 is exactly identical to one on 125.025. The 0.005 add-on merely tell the receiver in an 8.33 radio to select a tighter selectivity.
Most UK “GA” 8.33 channels have been implemented in this way – adding 5kHz to the old 25k channel.
Peter wrote:
It all works perfectly. The transmission on 125.030 is exactly identical to one on 125.025. The 0.005 add-on merely tell the receiver in an 8.33 radio to select a tighter selectivity.
It doesn’t always work perfectly (on a 25kHz radio) – given that a 25kHz radio is likely an older one, it may have drifted off frequency a little. When using a 25kHz channel, if the transmitter is 2kHz high or low you won’t really notice, but it’ll sound pretty scratchy if you try to listen to the same radio on the equivalent 8.33kHz channel. If it’s 3kHz off it’ll still be readable on a 25kHz receive channel, but it’ll sound unintelligible on the 8.33kHz receive channel as all you’ll have left will be a sideband and very little of the carrier.
