2-Port Cable and Antenna Analyzer for Tower Top and Duplex Applications Performance enhancing design trends such as high sector to-sector isolation, tower-mounted amplifiers and duplexed antennas add new complexities to site installation, deployment, maintenance and troubleshooting cables. To help simplify performance verification for these systems, the Site Master ™ Handheld Cable and Antenna Analyzer Model S251A features a second test port for isolation, gain and insertion loss measurements.