A few weeks ago I started a thread about the loss of signal to two GPSs on a flight to Duxford. Amongst the suggestions, was the possibility that the radio in the aircraft could be the cause. Well it was. We flew the same aircraft this w/e and experimented.... When one of the radios was tuned around 119MHz, both GPSs lost the satellites. There are two sets, a Narco and a vintage King. The Narco was the culprit.
So thanks to the person who made the suggestion, and a warning to others using a portable GPS - be aware!
