$re = '/\sx\s(?:[0-9]{2}\s){2}(.*?)\s[\w]{3,}/';
$str = '22.665774 Fr RMSG 0 0 1 1 18 11 Rx 0 308002 5 20 1d6 x 20 20 a8 4f 35 40 1b 00 0f 08 f7 89 ff fa ff f3 35 80 49 00 00 00 00 30 00 00 80 ab 4b 54 40 f0 00 fc 714a81 1 40937';
preg_match_all($re, $str, $matches, PREG_SET_ORDER, 0);
// Print the entire match result
var_dump($matches);
Please keep in mind that these code samples are automatically generated and are not guaranteed to work. If you find any syntax errors, feel free to submit a bug report. For a full regex reference for PHP, please visit: http://php.net/manual/en/ref.pcre.php