Comb generator design

I am trying to design a comb generator circuit of frequency range 30 MHz to 1GHz in NI multisim student version 13. I have designed a circuit with voltage regulator for which 5V is fed to the 74ls04d hex invertor. I am using 11 MHz crystal oscillator. The output of hex invertor gives square wave output which i gave to high pass filter to get spikes then gave it to the clipper circuit to clip off the positive spikes. when i observe the output in spectrum analyzer the impuse response is not repeating on a step size of 11MHz.What is the reason behind it and how can i sove it? Also how can i replace the diode of clipper circuit with step recovery diode?

hmmm. you are mixing up a LOT of different concepts.

A hex inverter will basically put out a square wave. If you are driving it at 11 MHz, you should see 33 MHz, 55 mhz, etc odd harmonics, and little even harmonics.

I do not knowhow good your simulator is, but a LS logic gate will not have much harmonic content above 50 MHz...they are just not that fast. There ARE gigabit logic chips that can switch that fast, and THAT is what you need to use to get harmonic content up to 1 GHz. you need a fast rising edge to get high frequency content.

Your highpass filter sounds good. I would them follow it up with a medium power amplifier stage, and see what comes out.

A step recover diode will not do much unless you USE it properly. the key to a step recover impusle generator is driving a series inductance with a big SINE WAVE, and then hitting a shunt mounted step recovery diode. The SRD will conduct on the positive half of the sine wave, and momentarily conduct on the negative going half but then suddenly, as the last charge carriers are swept out, the diode current will drop to zero. THe current in that series inductance needs to then go somewhwere, and it produces a whopping big voltage spike....that has a lot of harmonic content.

if you want to generate a spike with a lot of harmonic content, try an XOR gate (a fast one), like this:

Width of the spike output will be approximately the delay time. Delay can be a transmission line, or a gate(s). if you play around with FFTs, you will find that to get a high frequency harmonic content out, you need a NARROW PULSE WIDTH.


http://www.potatosemi.com/potatosemi...t/PO74G86A.pdf

What could be the simple circuit diagram of PO74G86A and crystal oscillator ? Is it ok if i use PO74G04A instead of 74LS04D hex inverter? I tried using PO74G04A and got only few harmonics as in fig why is it so?
http://obrazki.elektroda.pl/7336649700_1498973932.png
http://obrazki.elektroda.pl/8687529400_1498973005.png