Looked using my Rediffusion off-air tuner this morning. With a monitor locked to my lab SPG I could see faint traces of something down in the noise on some channels. I checked my SPG yesterday against off-air subcarrier (last chance!) and found that the master oven oscillator was well within 0.1ppm. Hence any off air reception would be effectively stationary on the screen.
Then the penny dropped. I was picking up radiated shash from my lab equipment. Moving the aerial lead around the SPGs etc varied the effect
