This is a string of attenuators that was attached to a transponder tester. It consists of one Comant CI-511 12db attenuator, plus two generic (Mini-Circuits) 6db attenuators (for a total of 24db) connected to a coax cable. I believe the ATC600A transponder tester requires 34db, so it might not be sufficient for said tester, so be sure you know what you are doing. Sold as is, no returns or refunds.