You're right Werner, the purpose is to adjust some parameters as frequency for a RF transmitter. The commercial HF transceivers have these coders.
It's also like the one we can found on some RF generators or function generators.

I'm still thinking that the coder+agilent choice is too expensive for this kinf of application. The adjustment tool will have the same cost than the device itself !

That's why I'm looking for a low cost solution. As I've seen low-cost coders for less than 1.5 euros, it gave me some good hopes. But now with that it has been said ...

Regards
Stephane