Headphone attenuator - This relatively easy project is ideal for SWLs and licensed. Some modern radios have a headphone ¼" jack socket output with high signal but also high residual irritating background hiss. Turning the volume down does not help. Instead, I install two 510Ω (550Ω preferred value) resistors (one for each channel) in the plug of the headphones. You can get large body plugs or make up an external patch lead (see photograph below) with the resistors in series with the typically internal red and white wires of the cable avoiding the third wire commonly known as the shield or screen. That would be less invasive to the headphones.


The resistors are quite fragile so you may pot the inside of the plug cover with silicone sealant to provide strength and insulation after soldering. The white plumbers' PTFE tape helps to secure the cover to the jack plug when assembled. I did try 330Ω resistors on my first attempt but the hiss from some radios required 550Ω.

This simple attenuation enhances my enjoyment of the hobby when listening in a quiet room and enables me to cause minimum distraction to others. If operating contests then it is invaluable to minimise listening fatigue which in this time of similar radios and ancillary equipment could prove to be a tie-breaker. Information and photograph also available on my website

73 Bob G4PVB
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