Transponders
This is a cross post from some of the other forums. It's been put here too to increase visibility and hopefully, generate a useful reply! Any assistance will be gratefully received.
As we all know, the transponder modes used by light aircraft in the UK are Mode A (aircraft identity), Mode C (altitude reporting) and – in the near future – Mode S (Selective reporting).
Mode B is mentioned by one internet source as being used in some countries instead of Mode A, while the sources all appear to agree that Mode D is not internationally established. Arising from that, I have several questions for the technical types:
· What is the difference between Mode A and Mode B?
· Are 3/A4096 transponders interoperable with Mode B interrogators (and vice versa)?
· What is Mode D?
So far as Mode S is concerned, can someone confirm for me that, despite the transponder automatically sending a unique address indicator to ATC, the pilot still has to enter a Mode A squawk code (possibly merely to identify who is controlling the aircraft or its task)? The photo’s I’ve seen of Mode S transponders still have the Mode A setting dials. Some of the articles on the internet are a little unclear and imply that a squawk still has to be input.
Can anyone assist, please? If anybody can suggest where I can find out more (particularly on the Mode B and Mode D points) I’d be grateful.
P
(PS I’m aware that the civil transponder system is a development of the military IFF system; that the military use Modes 1-4 inclusive and that the only Mode that IFF and transponders have in common is Mode 3 which is similar to Mode A (hence the oft seen 3/A prefix)).