As a person on the 'other end' of the SSR can I ask a few questions?
PM me if you want to answer to me privately.
How much is a Mode-S transponder?
How old is your current transponder?
How often do you get your Mode A/C transponder serviced? (Do they check power output, receiver sensitivity?)
The reason why I'm asking is that many older transponders on small aircraft are difficult to elicit a response from (due to some aircraft only having one antenna and the aircraft masks it in a turn and/or possibly poor maintenance) and when the primary is having difficulty in seeing the aircraft too it renders these aircraft as invisible!
So wouldn't a new well-maintained Mode-S transponder make sense?