Video Tutorial: Basics of an RF Comb Generator...

[w2aew]

...what it is, how it works, and some basic applications and uses for it...

[awallin]

nice video. +1 and thumbs up! 

questions:
1. in optical frequency combs (with which I am more familiar) there are two parameters, an offset-frequency, and the repetition rate. the comb teeth are at:
f_out = f_offset + n * f_rep
Are you saying that the offset-frequency of an RF-comb-generator is always zero? i.e. the teeth are exactly at:
f_out = n*f_rep ?

2. If you put a narrow-band filter around the n:th harmonic of the output, you'll get more or less a sine-wave at n*f_rep.
Is this n*f_rep sine-wave always phase-coherent with the input? i.e. there are  no cycle-slips and there will always be n cycles of the harmonic for each cycle of the input waveform, and the relative phase will not drift?
This has to do with my first question, since  in optical frequency combs you need to use phase locked loops to stabilize both f_offset and f_rep  in order to get phase-coherent output.

AW

[w2aew]

nice video. +1 and thumbs up! 

questions:
1. in optical frequency combs (with which I am more familiar) there are two parameters, an offset-frequency, and the repetition rate. the comb teeth are at:
f_out = f_offset + n * f_rep
Are you saying that the offset-frequency of an RF-comb-generator is always zero? i.e. the teeth are exactly at:
f_out = n*f_rep ?

For a simple SRD based comb generator, yes.  For more theory on the SRD based comb generator, check out the HP Frequency Counter Teardown and Repair video by TheSignalPathBlog.

2. If you put a narrow-band filter around the n:th harmonic of the output, you'll get more or less a sine-wave at n*f_rep.
Is this n*f_rep sine-wave always phase-coherent with the input? i.e. there are  no cycle-slips and there will always be n cycles of the harmonic for each cycle of the input waveform, and the relative phase will not drift?
This has to do with my first question, since  in optical frequency combs you need to use phase locked loops to stabilize both f_offset and f_rep  in order to get phase-coherent output.

AW

It will be reasonably stable with respect to the input, but you have to remember that the phase noise gets multiplied up with the harmonic, so you'll probably need to clean it up.

[German_EE]

From some research this afternoon step recovery diodes appear to be very rare and expensive devices, I therefore went looking for an alternative and I found the following:

http://www.ke5fx.com/cg.htm

This RF Comb Generator uses reasonably easy to obtain components with a pulse width of about 1nS and output beyond 2,5GHz.