The DC-Blocker must be used if you want to measure active powered antennas like GPS or satellite dishes. It prevents the RF-input of the SPECTRAN to be destroyed by the DC-voltages. Simply connect the DC-Blocker to the RF-input of your SPECTRAN and you can measure directly on GPS, satellite antennas or even DSL/ISDN etc. lines.
Fits to all Spectran HF & NF Analyzer.