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Hi Steve ... inline -joel Stephen D. Anderson wrote: From what I recall, there was much discussion on the ending frequency earlier on. 15Ghz was agreed upon by many people that believe otherwise. I want to be careful not to open that up again :)! Think 50Mhz to 15Ghz :). I don't know where this came from ... certainly not from me. Back drilling helps to eliminate effects from resonance structures, reflections, and potential standing wave concerns ... from my perspective. And I'm sure there are many other perspectives based on individual experience. Regardless of back drill, and WITH reasonable design practise, the channel can very by up to 10dB in the band above 5Ghz, and up to 5dB below it from mfg process issues with the glass. I would reverse your percentages. 1dB variance is easy to see from mfg. The reason we paid so much attention to Dk and Df is to put the effects into perspective and make sure they are included: - etch width - XY shrinkage - drill deflection - material thickness tolerance - resin structure variance - thermal effects - humidity - copper geometrical variance - copper thickness Including all this gives us the original SDD21 numbers I submitted for use. I think the model I submitted last gives us the changes at the lower freq with minimal effect on the upper frequencies. Though, I do agree with Joe that we could create a two piece equation if the higher freq variance really hurts. I perfer to keep one equation and one set of variables ... but that's just me. Take care -joel
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