I have a mini ir extender (transmitter of smarthome ir mini extender set or terk ir-4) could somebody help me to modify this units rf frequency from 418kHz to 433.92mHz.
Thanks

Why? That would help answer the question.

On the other hand -- what kind of circuit does it use?

Here's the 1980 garage-door transmitter adjusting routine --

Start with the 418 mHz receiver that should have come with the transmitter. Open it up and probe around while transmitting, and find a place where you can connect an oscilloscope probe and see some kind of signal directly related to RF from the remote being picked up by the receiver.

Once you have that, open up the transmitter and see what you can adjust. If the signal is crystal controlled, you are out of luck. If there is a fixed capacitor and a coil in the air, you will have to gently tweak the coil open to raise the oscillation frequency. If there is a trimmer capacitor, note its position and then adjust it. In either case, watch the scope for signs of the signal dropping off. If the signal drops off, then you have found something that adjusts the transmitting frequency.

Now open up the 433.92 mHz receiver, probe for a place that gives you a signal when it is receiving RF, and tweak the transmitter, looking at the scope for signs of a signal. If you get one, adjust the transmitter for the highest signal indication on the scope.

If this does not work, then set up the original 418 mHz receiver and see if you can get the transmitter back to the original frequency. If you can't, then that piece is trash. Sorry.

Ernie

Thanks,
I will try it.
I will use it with palm remote and powermid to control x10 in europe. This small unit is only produced in us freq. I have to modify it.
If somebody knows usefull links, please let me know.
Thanks Ernie