This unit clamps on the bottom of my 260 (Series 6) VOM. It is called "Communications Tester" Model 658. It measures SWR -RF Power -% Mod -RFS. It has a slide rule on it's face and a telescoping rod antenna. It has SO-239's on either side, and jacks for RF out and also AM Monitor. It has scaling up to a KW. Sadly, Simpson doesn't have any paper on it. Thanks in advance for any info. at all. Happy Holidays to all. (((((73))))) Les ---===WB6ORZ===---