Ciao FISICO,

te faccio un esempio
codice:
<script language="javascript">
function DecheckRadio(rr){
  if(rr.length){
    for(i=0;i<rr.length;i++)
      rr[i].checked=false
  }else rr.checked=false
}
</script>
<form>
<input type="radio" name="NomeRadio" value="1">
<input type="radio" name="NomeRadio" value="2">


<input type="button" value="deCheck" onclick="DecheckRadio(this.form.NomeRadio);">
</form>