BYPASS CAPACITORS

[KL7OF]

    Reading in the '77 ARRL HANDBOOK about bypass capacitors and there is this table that shows the approximate series-resonance frequencies of ceramic disc bypass capacitors.  (page 553)  with short and long lead lengths.  Cap values from .1 to .0001.  Freqs from 13mhz to 165 mhz.   Example:  .0001 uf with total lead length of 1/2 inch =165 mhz.  does that mean that the .0001 will bypass all freqs up to 165mhz or just those close to 165mhz?  
   The standard seems to be .1 or .01 for bypassing lines in HF amateur circuits.  These values only bypass lower HF freqs.  In HF amplifiers there always seem to be some VHF gremlins to be dealt with.  Usually handled with parasitic chokes in the plate and screen circuits, but can bypassing other connecting wires with bypass caps that act in the vhf range be helpful.?   example : Would it be helpful to bypass an amp plate supply with 2 caps, one to bypass HF freqs and one to bypass VHF freqs?  filament lines, AC lines, Control and relay lines, lines coming in....lines going out.......??      From the handbook........

1/2 inch total lead length ceramic disc cap

Uf        Mhz  

.01      15
.0047   22
.002     38
.001    55
.0005   80
.0001   165    

[w8khk]

Steve,

In an article written by Steve Summer on page 65 of the May 1963 QST, the technique of using the capacitor lead length as an inductor to provide a series resonant bypass is described in reasonable detail.

I sent some data to your email address in QRZ, hopefully it will be helpful.

73,
Rick

[Opcom]

Tis true.. caps have different resonant frequencies and that can be affected by lead length and tack length on SMD boards.

Debugged many a DSL modem design because of our customers' overseas manufacturers' unauthorized cap substitutions. They subbed to cheaper or different caps than specified and/or slightly changed track length and it messed up the filter tuning, decreasing performance at the longest line lengths. What a nightmare of extremely picky stuff that was. A worthy job though.

Today's caps may have slightly different series resonances than the caps of the handbooks' days, even with same lead length. I forget now the instrument used to analyze that.