tht is correct the VCO will give it the input frequency ... but u see the comb pattern is seen after the FFT of an impulse generated, this i plan to achieve by using a step recovery diode... i read the HP application notes available.. but then i dont see which step recovery diode to use and hw will the circuit actually look like.. so was also thinking of looking on the lines of sfwre implemtation done using MATLAB.... also hw to use a band pass filter to get almost unifirm power distr thru out the comb pattern.... so further help will be appreciated.. thx..