BFO in the A320

[DC-8]

Hi all!

Could anybody explain me a little bit about the BFO function which is below the ADF line in the R-NAV page of the MCDU?

As far as I know BFO is used two receive A1A modulated NDB's, but I don't know what's the difference between a normal NDB and a A1A one in terms of use. Is there any difference in accuracy or something like that?

This evening I selected MA NDB of LEMD (which is not underlined in the chart, so it is not A1A) in the MCDU with the BFO function active, but I couldn't hear the morse code, just a continuous chime. How would I hear an A1A NDB with the BFO function?

Thanks for your help!

DC-8