<script language="javascript"><!--
function clear_all_radios(){
    var lb = "\x5B";
    var rb = "\x5D" 
    var elements = document.getElementsByTagName('input');
    var elnum;
    for(elnum=0;elnum<elements.length;elnum++){
        var el = eval("elements"+lb+"elnum"+rb);
        if ( el.type == 'radio') {
            el.checked = false;
        }
    }
}
//--></script>
<p><a href="javascript:clear_all_radios()">Clear All Radiobuttons</a><
+/p>
[download]

Thanks to jZed for the parent node, upon which this code is based.

See also: planetscape's Free Nodelet Hack: Check or Clear all "Delete" Message Checkboxes in Your Message Inbox