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Aircraft Strobe Noise

Q. I replaced my rotating beacon with a strobe in my Cessna 182. The strobe makes an awful noise in my radio. I don't notice it as much during the day but at night it is awful. On long flights I've had to turn the strobe off. How do I get rid of the noise?

A. Strobes can product two types of radio interference; a high-pitch warble followed by a pop. Each type requires a different fix. The popping noise radiates from the strobe and is picked up by the antenna. You need to distance the strobe from the antenna or shield the strobe from the antenna. If you have a Whelen strobe then you can buy a shielded lens from Whelen that should eliminate most of the popping noise (15-17 dB attenuation). The high-pitch noise conducts from the strobe, through the aircraft's electrical system and into your radio. The wiring to your strobe probably consists of an unshielded power lead to the strobe and the airframe used as the ground return path. By placing a suitable size ferrite choke on the power lead as close to the strobe as possible you can eliminate almost all the high pitch noise. The ferrite choke blocks the high frequency signals that cause radio noise.

The Radio Shack ferrite choke (part number 273-104) works good. You can snap it apart, loop the strobe power lead around it as many times as possible and snap it back together. Ferrite material is heavy so you need to support the choke to prevent vibration from breaking the wire connection. I have also used small ferrite beads that slip over the wire but these are less effective for strobe noise.

Another solution is to use a Electronic Noise Filter such as the Lonestar LS10003-06 (available at Sky Ranch) This is a compact (6 oz.) low pass double PI type DC power line filter and is FAA/PMA approved.