Hi, Venu does not have any board detail. If you have a high frequency Scope we can calculate the Er as follows. Find a visible PCB track on the top layer ( call it microstrip ). Feed a fast rising edge on one end of it and observe the rising edge at the two end of known length ( L) of the microstrip. Find the skew between the two signal. the propogation delay in ps of microstrip is roughly t = L * 85 * sqrt ( 0.475 * Er +0.67 ) ps , L is in inch For example, if L = 4 inch skew t = 570 ps Then , Er = [ ( t/ 85*L)^2 - 0.67 ] / 0.475 = 4.3 TDR can also be used. Thanks Vikas Shukla jeff_latourrette@xxxxxxxxxxx wrote: Venu: One other tiny issue with microstrip is that in addition to frequency dependence, the effective dielectric constant is also very geometry dependent, on width and to a smaller extent the thickness: epsilon(eff) = (epsilon(r)+1)/2 + [(epsilon(r)-1)/2]*f(W/h) - [(epsilon(r)-1)/4.6]*(t/h)/sqrt(W/h) where, epsilon(eff) = effective dielectric constant epsilon(r) = dielectric constant f = frequency W = microstrip line width h = height (of dielectric between ground and line) t = microstrip line thickness from Bahl & Bhartia "Microwave Solid State Circuit Design" Basically the wider and thinner the microstrip line, the more of the field is contained in the dielectric, beneath the trace and the higher the delectric and slower the velocity of propagation. High impedance (narrow) microstrip lines have more of their field in the air, which also makes them more susceptible to crosstalk. Cheers, Jeff LaT -----Original Message----- From: Tim Hochberg [mailto:tim.hochberg@xxxxxxxx] Sent: Friday, July 18, 2003 7:06 AM To: cclewell@xxxxxxxxxxxxxx; 'Peterson, James F (FL51)'; si-list@xxxxxxxxxxxxx Subject: [SI-LIST] Re: Finding Er (Permitivity) Another issue is that, for microstrip, this is going to give you the effective dielectric constant, not the actual dielectric constant. If you can use stripline instead, this won't be a problem, otherewise your going to need to try to recover the dielectric constant from the effective dielectric constant. This will be a little bit approximate since the effective dielectric constant is frequency dependant. However, the dependence is week, and there are effective dielectric calculators floating around on the web, so you should be OK. Regards, Tim Clewell, Craig wrote: >Jim, > >I've got a big bat . > >You are correct...sorry about that. > >Thanks for the clarification. > >Craig > >-----Original Message----- >From: Peterson, James F (FL51) [mailto:james.f.peterson@xxxxxxxxxxxxx] >Sent: Friday, July 18, 2003 9:25 AM >To: cclewell@xxxxxxxxxxxxxx; 'kamal_elx@xxxxxxxxxxx' >Cc: si-list@xxxxxxxxxxxxx >Subject: RE: [SI-LIST] Re: Finding Er (Permitivity) > > >craig, > >it might be a pretty big ballpark!! >you would have to square the equation to get Er. > >Vp(m/s)= 3e8(m/s)/sqrt(Er) >so >Er = (3e8(m/s)/Vp(m/s))^2 > >regards, >Jim > >-----Original Message----- >From: Clewell, Craig [ mailto:cclewell@xxxxxxxxxxxxxx > ] >Sent: Friday, July 18, 2003 8:40 AM >To: 'kamal_elx@xxxxxxxxxxx' >Cc: si-list@xxxxxxxxxxxxx >Subject: [SI-LIST] Re: Finding Er (Permitivity) > > >Venu, > >If the board is a Microstrip you can do a quick measurement of the delay and > >use this value to calculate the E'r. > >Use E'r = 3e8(m/s) / vp(m/s) > >where vp = propagation velocity = inverse of the delay. This should get you > >in the ballpark > >Regards, > >Craig > >-----Original Message----- >From: Kamal EC [ mailto:kamal_elx@xxxxxxxxxxx >] >Sent: Friday, July 18, 2003 7:25 AM >To: si-list@xxxxxxxxxxxxx >Subject: [SI-LIST] Finding Er (Permitivity) > > >Hello Everybody, > >I am having a PCB Board for which I want to calculate the Permitivity. I >don't know what material is used for the pcb. >I don't have any details of the board, except the fabricated board. > >Is there any method by which i can calculate. > >Regards, >Venu > >_________________________________________________________________ >It's new, it's here! 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