If your cable TV picture is distorted or the audio is accompanied by a hum, a ground loop may exist on your line. A ground loop occurs when your electronics have more than one path to a grounding source. Electrical noise is introduced to your cable TV system, and results in poor quality video and audio. A homemade ground loop isolator blocks DC and low-frequency AC current from the line, allowing the higher-frequency video and audio signals through.
Check the DC continuity of both transformers. Set the multimeter to the highest resistance setting. Depending on the transformer, apply the positive probe to the F-connector threads or shield and the negative probe to the terminal forks or screws. The meter should read infinite resistance, or zero continuity. At least one of the transformers must block DC continuity.
Connect the female transformer's terminal forks to the L-shaped male transformer's terminal screws.
Connect the coaxial TV cable to the female F-connector. Connect the L-shaped male F-connector to the female input of your TV or VCR.
A transformer should block DC continuity, in theory. Test the transformers for zero continuity to verify there are no manufacturing defects.