ADF ident audio frequency?

[GarageYears]

I have a rather specific question regarding the operation of ADF receivers within Europe and specifically the UK. Currently I'm working on the comms system for a Level D FFS and have been asked to look at the ADF simulation.

We are looking at a defect report that states the audio tone used to replay the ADF ident is the wrong frequency. According to the ICAO, FAA regs, etc, the audio tone that is keyed to make the ident audible is either 400Hz or 1020Hz.

On all previous simulators we have used 1020Hz without comment, and have only used 400Hz in conjunction with the BFO or Tone switch to receive older non-modulated carrier NBDs.

However this time the test pilot we are working with has stated that the ADF tone is incorrect (the higher 1020Hz one), and that all ADF stations in the UK (and possibly much of Europe) should be heard using the lower 400Hz tone.

For reference, 1020Hz is the tone frequency used for VOR/ILS tones, while 400Hz is used for the ILS outer marker.

It would be very helpful if any pilots reading this could offer their opinions.

I realize that trying to recall what one tone versus another sounds like after the fact is tricky, but right now I have nothing.

Thanks, GY

[hetfield]

As far as I remember it's 1.020 Hz.

cheers

[DFC]

In the UK, 400Hz is required.

[eglnyt]

The modulation frequency for NDBs in the UK is 400Hz (CAP670 Section 2 Nav 02)

[hetfield]

ADF
Identifying Tone
Q. Are there any NDB (Non-Directional Beacon) stations that still use 400 Hz tones for the Morse Code identifier? ICAO (International Civil Aviation Associaton) states that in addition to 1020 Hz tones, 400 Hz may also be used.

A. The ICAO world standard does specify that an NDB audio ident may be either 1020 or 400 Hz. But in many years of flying and tuning hundreds of NDB's we've never heard a 400 Hz tone.

Practical Avionics

[GarageYears]

Thanks to those that have replied so far. I also found the Practical Avionics article, but I suspect they are US-based.

However thank you "eglnyt" - that CAP 670 document has exactly what I needed, and indeed confirms that NDBs within the UK are 400Hz.

Now I wonder how all those previous sims were certified or at least wonder why this has not been DR'd before?

Is there a similar document for Europe? Is that under EASA control now?

Thanks, GY

[411A]

One has to ask...what does it matter what the frequency of the tone is...you either ident the frequency, or not?

And, some don't.

[GarageYears]

I suppose you could ask the CAA, FAA or similar why it matters?

A Level D FFS is supposed to represent the original aircraft as accurately as possible. If the ADF tone is 400Hz in the UK and 1020Hz in the USA it should be accurately represented in the simulator. Otherwise the device is imparting negative training at some level, whether it matters to you personally or not. Learning to hear the difference between a DME ident (1350Hz) and an ADF at 400Hz probably is important to some.

- GY

[Loose rivets]

Yes, I recall hearing the very first DME idents. Even to my young ears it seemed very high after the melodious 400 cps. Oh, okay, Hertz.


Take the middle C on a piano and the A above it. Your 400 Hz will be very roughly between the two.

[BOAC]

It is very important - I know several KOS's (and some younger 'clubbers) who cannot hear the DME ident - that's if they listen!

[Loose rivets]

In the cold light of dawn, I realized that I'd erroneously remembered middle C as >361 Hz, but it's >261. So, very, very roughly between C and A

Interesting where the Soprano voice is expected to reach. Just about sing along with the DME they could. So, quite a waste of time young clubbers going to hear them.



Piano key frequencies - Wikipedia, the free encyclopedia