hello.
im trying to reduce a noise when recording with a mic.
clearly it is a radio signal from some station, could you tell me some possible reasons.

If you are saying that it is captured as you record, it means that some cable is acting as an antenna, perhaps the microphone cable. The input of your microphone preamp is then demodulating the RF signal. Or, if it is the cable from the preamp to the soundcard, the demodulating is occurring at the soundcard's analogue input. Something nearby may be receiving and reflecting or re-broadcasting the signal.

Sometimes just altering your (the equipment's) position will alleviate this. Possibly something needs to be shielded or grounded (yourself maybe). You may well need to experiment with moving and altering bits of your recording apparatus until it goes away.

how can i get 'grounded'?

im surrounded by a lot of things that could be doing the antenna thing.
by now i get a very low quality, i found my mic in a lost box, i use one adapter in the plug in.
what are the things or specifications i have to look foward in a mic.? (the mic is to record guitars with distortion and clean, voice)
with an adapter i lose quality?