Just been testing some kit with a DSP banging away at 150MHz and an AVR at 8MHz and was surprised to find that the AVR (Mega64) is much noisier than the DSP. Although we've managed to stamp out most of the noise (by removing a cap from an input rather bizarrely), you can see sniffing about with the spectrum analyser, the Mega64 running 8MHz is producing a surprising amount of 8MHz noise and a rather odd 160MHz harmonic on a line connected te a switch on a rotary encoder.
Anyway, my question is really on whether other people see the Mega64 as a noisy device? (I have good ground planes, decoupling etc and as the 150MHz DSP is quiet as a mouse I don't believe it's a layout problem.) Also, would sticking a Mega325P - which looks like it's the same pinout - give me any improvment? I instinctively think that a lower power device might radiate less, but that could well be fallacious thinking!
Many thanks. :)