Re: Transmission line-like resonances at ~30MHz

From: Chris Carlen (crcarle_at_BOGUS.sandia.gov)
Date: 02/10/05 

Date: Thu, 10 Feb 2005 07:35:14 -0800

Joel Kolstad wrote:
> I have a design on an FR-4 PCB that has a few long traces on it, about 12"
> each. When I examine those trace's responses on a network analyzer, they
> have significant (>15dB) dips at 30MHz, then 90MHz, 150MHz, etc... this led
> me to suspect that the traces were behaving like quarter wave transformers
> (the traces have various components connected to them, but they're all
> supposed to be pretty high impedances), but if I assume an effective
> dielectric constant of ~2.35,

I think FR-4 has mu_r = 4.7 

-- 
_______________________________________________________________________
Christopher R. Carlen
Principal Laser/Optical Technologist
Sandia National Laboratories CA USA
crcarle@sandia.gov -- NOTE: Remove "BOGUS" from email address to reply.

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