I'm using an AVR Mega32 in the DIP40 package to interface with 35 MHz remote control radio transmitters and have found that there is an enormous radiated emission from the AVR at the second harmonic of the
16 MHz crystal. According to my spectrum analyzer the 32 MHz emission is 40 dB at 25 cm, while the output of the transmiter at 1 m with the antenna down is only 45 dB.This noise is reducing the effective range of the remote control from nearly 1 km to less than 100 m before the receiver can no longer hear the transmitter. I've verified that the AVR alone is causing the problem; on a breadboard with just the microcontroller, decoupling caps and crystal the noise levels are identical. There is no radiated noise at 72 MHz, so it works fine with the US transmitters.
I've tried a variety of replacement chips, chokes, caps and shields to no avail. I even tried a Mega128 in TQFP packaging and found a similar amount of noise. Does anyone have any further ideas?
Thanks,
-- Trammell