If you are thinking of buying a transponder, Paul, you should buy a mode S
transponder. You are correct that a lot of the ATC units you may contact
will not be Mode S equipped, but they will still recieve the mode A and
mode C (4 digit assigned code and altitude). Buying a non-mode S
transponder would be a waste of money, as you will need it to enter
certain areas and types of airspace in the UK. A transponder mandatory
zone means a mode S transponder mandatory zone.

At 19:15 12 September 2009, Andy Melville wrote:
As a very uneducated pilot,following Paul Remdes suggestions, I was
considering buying a Transponder mode S but then various people said
local
airports didnt have mode S yet so it woulld be a waste of time for some
time to come..is this true?
If I buy mode S can it be accessed/ used by the current systems?
Some easy to understand stuff would be most welcome!
Regards from UK