bfo

[luc]

can someone explain what is the difference between a bfo and non bfo adf?

[Grendel]

Some low freq beacons are modulated in such a way that an additonal oscillator to produce an audio frequency tone.

The Glossary of "Aircraft Radio Systems", J. Powell says that a Beat Frequency is the difference frequency resulting when two sinusoids are mixed in a non linear device, ie modulator.

Some very basic low freq beacons, mostly in the third world, are unmodulated and the bfo switch on the receiver applies a reference radio frequency to the incomming signal and you hear the diference, or audio portion.

[DC-8]

Hi,

Try this link: http://www.pprune.org/forums/showthread.php?t=236803&highlight=BFO+in+A320

[411A]

On some older ADF's fitted in airline aircraft, those with continuous tuning versus digital selection, the BFO was used to tune the exact center of the desired frequency.
It was very useful on some occasions, especially when doing manual (instead of automatic) bearing exercises.

How long ago?
DC-4, DC-6, DC-7, Constellation, and many older B707 aircraft.

[BizJetJock]

Grendel,
Are you counting France as the third world in that?:ok: Most French NDB's require the BFO to ident.

[luc]

thank you. all clear now. apart from the bit about France and thirld world...

[sugs]

Shortly line checking to France and wondering if anyone can answer the following, as Aerad FIS does not elaborate and looking at various charts, there seem to be inconsistencies. How do you know whether an NDB on an AERAD approach chart is A1 (ie requires BFO for ident), before you actually get in range to discover no ident. I previously thought it was the lack or presence of upper 'commas' but can't seem to find where this info is located. Thanks in advance...

Sugs

[OzExpat]

Now this might be a radical idea but it occurs to me that if you don't hear the ident without BFO selection, it might be an idea to select BFO and listen again. I've found this to be quite a successful plan, pretty much anywhere in the world, if the navaid is actually working. Of course, you probably should start thinking about that while you're at least 30-50 miles (50-80 Kms) away from the navaid.

If you think ahead, a bit, that shouldn't be too much of a problem.

[keithl]

Nice thought, OzEx, but it might not do for someone doing a Line Check. These Checkers! They expect you to know in advance. Your suggestion is trial-and-error, and that doesn't always go down that well...

[sugs]

Thanks for the suggestion OzExpat. However as my question clarified (if read carefully), I was wanting to discard this logical technique for a process based on knowledge. Keithl has got the idea. It's a checker thing...
Thanks again

Sugs

[excrab]

Sugs,

The information is in the aerad enroute supplement (yellow), com section. All the frequencies for each airfields nav aids are given, along with the type of modulation - for example all the locator beacons for CDG are listed as A1A. The explanatory notes on com page 1 has a long explanation of NDB emissions and when to use the BFO which I won't try to reproduce here, but as has been stated previously most french NDBs are A1A or N0NA1A and need the BFO to ident them.

Hope that helps. Now that you know you could ask the line trainer the same question at the start of the check. If he/she doesn't know then they could be kept busy for hours on the jump seat searching through the ops manuals and thus not notice what you are doing wrong in the mean time.

[sugs]

Thanks excrab! Quality answer; have been searching Flight Info Supp, and should have thought to look in the other. I knew it had to be somewhere, but still feel that it used to be interpreted directly from the chart in some way. Maybe not anymore.. Thanks again for your time,

Sugs

[IRRenewal]

It's been a while since I used Aerad, but on a Jeppie plate the identifier of an NDB requiring the use of the BFO is underlined.

Pretty sure Aerad do something similar. There should be a legend booklet with your Aerad manuals, otherwise check a UK plate and a French plate and see if you can spot a difference.