Re: [SI-LIST] : Cavity Resonant frequecy and radiated EMI

About this list Date view Thread view Subject view Author view

From: Doug ([email protected])
Date: Sun Sep 24 2000 - 20:51:41 PDT

There are several modes to resonance in a cavity.
Need to know height, width, and length to accurately
predict anything.

Regards, Doug

"KHOO,KENG-KOK (HP-Singapore,ex4)" wrote:
> Hi all,
> I have somne questions on the cavity resonant frequencies. I found a formula
> in Noise Reductions Techniques in Electronics System by Henry Ott Pg.199
> that says
> f = 212/L,
> where:
> L is the largest dimension of the cavity in meters
> f the lowest resonant frequency in MHz
> I have a rectangular box with L=140mm so f = 1.514GHz.
> There is a cable running out of the enclosure and the cable lenght inside
> the enclosure is 210mm and 430mm on the outdside of the enclosure. Radiated
> EMI measurement shows cable emission around 100-150MHz.
> Enclosure
> 210mm | 430mm
> --------------|----------------------------------
> Inside | Outside
> Ferrite core works well in reducing the 100-150MHz emission when it is put
> on the outside of the enclosure but did NOT have any effect when put on the
> inside portion of the cable.
> Questions:
> How do I relate the 1.5GHz resonant frequency to the 100-150MHz emission
> from the cable?
> Have I interpreted the formula wrongly?
> Where did the 212/L formula came from?
> Thanks a lot.

**** To unsubscribe from si-list or si-list-digest: send e-mail to
[email protected] In the BODY of message put: UNSUBSCRIBE
si-list or UNSUBSCRIBE si-list-digest, for more help, put HELP.
si-list archives are accessible at

About this list Date view Thread view Subject view Author view

This archive was generated by hypermail 2b29 : Tue May 08 2001 - 14:29:34 PDT