BFO in the A320
 

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

BFO stands for Beat Frequency Oscillator. When switched on it allows the operator to identify a NDB that has no modulated ident. Most NDBs consist of a continuous carrier amplitude modulated with an ident, usually at 1020Hz (A3A).
For these BFO off would be normal, however there exist NDBs that ident by defining their ident by simple on and off keying of the carrier (A1A), for these the BFO is needed to beat with the carrier and provide an audio tone that the ear can cope with to positively indentify.


Edit for spelling and improved clarity, posting intoxicated again.

These days it's mostly French Ndbs that require the Bfo on to ident them. Ones that spring to mind are the Toe (Tls) and the Nc (Nce). Without the Bfo, these will not ident aurally or on the Nd.

Cheers,
mcdhu

Yep here in the caribbean, in the French territories, you have to use the BFO mode to ident the NDBs. (Guadeloupe & Martinique)

Ok, thanks a lot for your help. Now I understand!

Nice flights!

DC-8

Thank you so much for explaning! I'm flying this type now for quite some time and nobody ever could explain it to me.

thanksfully,
Dani

BFO
 

Wodrick is correct...

If the radio transmitter were a simple AM broadcast transmitter, you would not need the Beat Freq Oscillator.

For example, there is a guy on the microphone with a high-pitched voice (underpants too tight) saying Dit-Dit-Dah-Dit (morse code)...then, you would be able to receive the message without a BFO.

But, if the transmitter were a simple morse code transmitter...like the Titanic sending a morse message for help...you'd need a BFO to receive. (In this case, the transmitter only transmits when sending a morse character. In the case of an AM broadcast transmitter, the transmitter is transmitting all the time...even when the guy talking is pausing for a breath.

By the way, when you receive SSB (single-side-band) on your HF, your receiver has a BFO operating. Without the BFO, you would be unable to receive side band. (This is because SSB is one side band [half of what you have with an AM signal] and has 'surpressed carrier'...which is close to a morse transmitter, in that, between words, the transmitter is transmitting a low-power signal. They do this for better effectivity...it concentrates the transmitter energy more into the words spoken...and doesn't waste the energy on a carrier...or both side bands.)


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