who can i make 555 timer as a noise generator for the band 35-45kHz?

Answer 1

I think you meant 'How' not 'Who' ☺

If you set it up to run as an astable multivibrator at around 1 or 2 khz and then feed the square wave produced into a bandpass filter with a passband of 35 to 45 khz, you should get a 'fair' approximation of random noise (actually, the sum of the Fourrier components of the 1 or 2 khz 'almost' square wave coming out of the 555).

But what you get won't really be all that terribly 'random' since it will be multiples of the 555's basic frequency. If you ran 2 (or more) 555's at frequencies that were not multiples of each other and then combined them in a simple analog adder and fed -that- through a bandpas filter, you'd get a lot 'flatter' power spectrum over the 35 to 45 khz band of interest.

HTH ☺


Doug