It was back in 2007 when I designed and built a simple comb generator to test the wideband response of RF filters.
An interested builder asked me for further details about my circuit, but it was so simple and flexible that the only help I could provide was to complete the circuit diagram.
The circuit shown above generates an uncalibrated and non-constant "RF comb" from the XTAL frequency well up to the 500 MHz region. The comb is good for relative measurements, such as peaking a filter.
Comb peaks were observed to be spaced as much as the base XTAL frequency: the smaller the rock, the more dense the spectrum will be. Note that you might need to increase C's across the XTAL for lower frequencies.
An alternative for much more dense comb in HF is the "VE3DNL Marker Generator", do a web search for references and diagram. I think both of these circuits should be in every builders' shack.