How is called a potentiometer like this?

I have a little project to do and I'm seeking for a potentiometer that can make infinite rotations (even if the cursor value doesn't change anymore). I have one in my radio and as it turns at maximum, it is slightly harder to turn it. If anyone knows what do I mean please tell me.

(nah, it's not an encoder)

I think you have a potentiometer with a slipping-clutch mounted on the shaft. Mentor 716. Safety Slip Coupling | Conrad.com

also google for "endless rotation potentiometer"

Skiermaxhtc:
I have a little project to do and I'm seeking for a potentiometer that can make infinite rotations (even if the cursor value doesn't change anymore). I have one in my radio and as it turns at maximum, it is slightly harder to turn it. If anyone knows what do I mean please tell me.

(nah, it's not an encoder)

What kind of radio? I cracked open a big old one my parents had and the knob was attached to the variable capacitor by a string and pulleys. When it hit the stop the knob would just rotate inside the string loop.

Continuous rotation variable resistors do exist. As said above they are usually expensive because they are for specialised applications and are of high quality. The output is in the form of a sin wave change of resistance as you rotate.

I think though if you think you have one in your radio, it will not actually be a continuous rotation variable resistor but instead a rotary encoder. These are used in a lot of audio equipment because they give digital signals to work with the modern fashion for digital control and processing of audio. The fact that they rotate continuously is incidental.

It can't be a rotary encoder, it has extra resistance past the endstops.

Here's a picture of what I mentioned. The big knob near the top corner is connected to the variable capacitor (the bunch of plates in a row on the left) by a string and pulleys. The big knob on this old radio has exactly the property you described: Once it reaches the endstop it will still rotate, but with slightly more resistance. It obvious to see where the extra resistance is coming from. Since the string can't move any more, it's sliding on the shaft of the knob, which produces friction.

Also note that it's usually not a variable resistor that controls tuning in an analog radio, but a variable capacitor.