Advertisers Tune In to New Radio Gauge In 14 locations around the Washington area, MobilTrak devices are sensing which radio stations drivers are listening to by picking up electronic signals emitted from car antennas. &lt;br&gt;&lt;FONT face="verdana,MS Sans Serif,arial,helvetica" size="-2"\ color="#666666"&gt;&lt;B&gt;-The Washington Post&lt;/B&gt;&lt;/FONT&gt;