Question for 8.33 rules knowItAll

[MarcK]

I see that this is all a bit of smoke and mirrors. ATC won't say "121.5", instead they will say "121.505" (i.e. the even 25kHz frequency names won't be used), even though the radio will actually transmit/receive on 121.500 MHz. So all of you who have been asked in the past to monitor 121.5 will now have to monitor "121.505".

Similarly, you can't select "118.25" on your radio. You select "118.255" which is really frequency 118.25 MHz. Then when you fly to the US you will have to add 0.005 to each frequency assignment. Except for VOR/ILS?

[Jan Olieslagers]

Bad example: 121,500 remains what it was, see #34.
But right about the 118,255.
VOR/ILS are not affected, AFAIK.

[MarcK]

But will the radio let you tune "121.500"? If you wanted 122.500 the radio wants to display 122.505. Does it know something special about 121.500? As I said, I don't have or need an 8.33 radio, so I haven't actually twiddled the knobs.

[The Fat Controller]

An 8.33 CAPABLE radio can select ANY current ATC frequency including 121.500 and will always be able to do so.

[Andrewgr2]

Unless it is an Icom A220. On this radio you have to go 2 levels into the menu to select a 25khz frequency when in 8.33 mode. A firmware upgrade to make it perform like everyone else’s radios is awaited. In the meantime it will be almost unusable in a mixed 8.33/25 environment.

[BackPacker]

Originally Posted by MarcK

But will the radio let you tune "121.500"? If you wanted 122.500 the radio wants to display 122.505. Does it know something special about 121.500? As I said, I don't have or need an 8.33 radio, so I haven't actually twiddled the knobs.

Yes, the radios are intelligent. If you select 122.500 on the radio, it knows it's a 25 kHz separated frequency. So it'll transmit on 122.500 but on receive will use a 25 kHz wide filter. On the other hand, if you select 122.505 it knows it's an 8.33 kHz separated channel. So it'll again transmit on 122.500 but on receive will use the 8.33 kHz wide filter.

All this is done to make the system fairly idiot-proof. You don't have to worry about 25 kHz or 8.33 kHz in reality. All you need to do is dial-in the frequency ("channel") that's been given to you, and the radio will take care of the rest. Also the 8.33 "channels" that are now being used cannot be tuned on a 25 kHz-only radio anyway, so that would hopefully give a clue to the pilot that he's doing something wrong.

(Unless it's an Icom A220, apparently.)

[MarcK]

Thanks. That makes sense. I hope this "improvement" never crosses the pond.