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[Discuss-gnuradio] interpolation and output level

From: Chuck Swiger
Subject: [Discuss-gnuradio] interpolation and output level
Date: Tue, 08 Mar 2005 08:46:33 -0500

Hi - Just curious whats the mechanism behind this: using a usrp xmit
interpolation of 64 we get max signal level, and it drops off a lot if changed, say to
40 or 80. With interp=64, sample rate of 2000000, sig ampl of 6000, center
at 14000e3 and freq of 72e3 my output is 3v peak (external amps).
Change it to interp=80, sample rate of 1600000 it drops way down to .6v peak
(-14db). Try 50, 3200000 and get .5v peak out. Even stranger using interp=60
gets 2.7v peak but 68 it's down to .6v.

This came up trying to dovetail sample rates between audio and the usrp.
64 doesn't come out an even multiple ( 2000000 / 32000 or 48000 ). Using
80 seems good ( 128000000 / 80 / 50 = 32000 ) just the signal level is way


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