The first gate is biased as a XTAL oscillator. I picked 10 MHz but any HF junkbox rock will probably do. Pretty standard stuff.
The second gate is a simple buffer for the oscillator output. Makes sense.
The third gate delays the signal of few nanoseconds, enough to produce -hopefully- a glitch in the 4th gate output. Will it work?
The R-R-R network is a simple ~10dB ~50ohm attenuator pad to match the impedance to 50 ohm loads (D.U.T. - Devices Under Test - mainly HF/VHF filters in my case).
According to my paperwork the comb peaks should be separated of half the XTAL frequency.
I've always wanted to put to a good use TTL gates propagation delay! Let's see...
