veex_veex 23/05/2013 17:41 Page 2
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Echo Margin
The Equalizer Coefficients will also reveal the presence of an Echo, (a.k.a. micro-reflections). The Equalizer will cancel such an echo, and in doing so the Equalizer Coefficient which corresponds to the delay of the echo will be much higher than the surrounding ones, 'sticking out of the grass'. The relative amplitude of this Coefficient is an indication of the seriousness of the echo, and its position gives the delay of the echo, hence its round-trip distance. The Echo Margin is the smallest difference between any Coefficients and a template defined by Cablelabs, as a safety margin before getting too close to the 'cliff effect'. It is normal to notice relatively high Coefficients close to the Reference as this corresponds to the filters in the modulator/demodulator pair and to the shape of QAM signal. include the Linear distortions to ??F?6FRF?R?V?F??bF?R6?v???'WBF?R?FV??GV?F?"6???B?W&FR&?W&?v?F??WBF?RWV??W"???FF?F????F?RWV??W"W6W2?U"2F???F?FF?fV?6?6V?F?R??V"F?7F?'F???2?6??6WVV?F??B?26??fV??V?BF?F?7F??wV?6??U"???????V"F?7F?'F???2????g&??V??WV??VB?U"???????V"?B??V"F?7F?'F???2??F?RV??WV??VB?U"?26?7V?FVBg&??F?R?U"?BWV??W"7G&W72?F?RV??WV??VB?U"?2?v?2v?'6RF??F?R?U"?6???F?ffW&V?6R&WGvVV?F?RGv???F?6FW2?GF?R??V"F?7F?'F???2??&vRF?ffW&V?6R??F?6FW2F?W&R&R7G&??r??V"F?7F?'F???2?WfV??b??V"F?7F?'F???2&R6?6V??VB'?F?RWV??W"?WV??F????2G???2&?6W722?BG&6?2??V"F?7F?'F???2'?G&???BW'&?"WfV?gFW"6??fW&v??r??&vW"??V"F?7F?'F???2??V?G2?&vW"G&6???rG&?6?V?G2??V?6R?F?W&R?2??&R&?&&??G??bG&?6?76???W'&?"?&R?dT2?"?7DdT2$U"??6?Vff?6?V?G2f?"V6?F&R&V?F?fV?7F&?R?v?W&RF?W?&RW?G&7FVBg&??F?RFV??GV?F?"?&V6W6RF?R6??f?wW&F????bF?RWV??W"?2???v???F?V?F?6??F?R??GVFR?B?6R&W7??6W2?bF?Rf??FW"6?&R6?7V?FVB??F?W"??f?&?F????2?6?f??&?Rg&??F?R6?Vff?6?V?G2?W6VgV??V7W&V?V?G2g&??F?RWV??W ??bF?RWV??W"6?Vff?6?V?G2&R&WG&?WfVB???6R?B?26??fW&vVB?v??BW6R6?&R?FR?bF?V??v?F?F?RWV??W"2f??FW"??B?2?'f??W2F?6?7V?FRF?R&W7??6W2?bF??2f??FW#???GVFR?B?6R&W7??6W2??W2F?Rw&?WFV??&W7??6RW?G&7FVBg&??F?R?6R????6R?&v???F?R??vW"F?R?U"?F?R?&vW"F?R&?&&??F?W2?bW'&?'2??G&?6?76????&R?dT2?BF?V??7B?dT2???U"FVw&FW2V?F??W'&?'2&R6??V?W&?W2F?BFWVFR6?v??&V6?fW'??2?????vW"?76?&?R?6?fbVffV7B?????6R?&v???2FVf??VB2F?R??V?B?b???6RF?B6?&RFFVBF?6?v??????F?W"v?&G2???r?V6??U"6?FVw&FR?&Vf?&R?BvWG2F?vW&?W6?6??6RF?F?R6?fbVffV7B???GVFR?Bw&?WFV??&W7??6W0??WV??W"7G&W72?BV??WV??VB?U ??F?RWV??W"6?Vff?6?V?G26??G&??F?R??V?B?b6?v????vW"?g&??V6?FF?B?2fVB??F?F?RWV??W"V???FW2f?'GV??????V"F?R&VfW&V?6RF?'?7V???rF?R?vW'2?F?7F?'F???2?bF?R??6???r?6?v???F?W&R?2?vW"WV?F?F?R?vW"?bF?R?6R??GFW"v?W&RF?R6?v??&W7??6W2&R??rvf?Br???V"F?7F?'F???2??F?R??6???r6?v???6??6WVV?F?WV??W"&W7??6W2&RF?R?6R??GFW"?26W6VB'???7F&??G??bF?R6%F?W6R?vW'2vW&R6WBFF?fV?F?&??6R6?R2F?B?bF?R6?v??W?6WBf?"???fW'&?W"?bF?R?6?v??26VV?BF?RFV??GV?WBF?R??V"F?7F?'F???2?6?R??GVFR'WB6????f?"F?v?v&B6??R?bF?R6?v???F?R?F?"?F??2??7F&??G?6?V?B&Rf?V?BBF?R??6?FR?6R?WV??W"?2?Wv&B6??R?F?R&W7??6W2???GV?F?"?BW?6??fW'FW"?"??F?RF?RWV??W"7G&W72?2FW&?fVBg&??F?R&R6?7V?FVBg&??F?R6?Vff?6?V?G2W6??r?&V6V?fW"?F?R?6R??GFW"??G&?GV6W2WV??W"6?Vff?6?V?G2?B??F?6FW2??r?F?V?F?6?f7Bf?W&?W"G&?6f?&?2?6??&6??Bf?'F?&?FF????bF?R6??7FV??F?????V6?F?RWV??W"?2F?v?&?F?6?6V?F?RfW'F??rg&??F?RF??RF????F?F?Rg&WVV?7?v?W&RF?R7??&??6?W7FW'2V???vFR?BvWB??V"F?7F?'F???2??B?2v??&???F?6F?"?bF??????F?Rg&WVV?7?7??bF?R6?7V?FVB6??6W"F?F?R7??&??( ?2&?V?F'??WfV?GV????V"F?7F?'F???3?F?R??v?W"F?Rf?wW&R?F?R&W7??6W2?2F?&V7F?&V?FVBF?F?R6???r6??R7??&??2v???7&?72F?R&?V?F'??B?W727G&W72?W&??B?bF?RWV??W"?7??&??W&??B?6W6R?W'&?"??G&?6?76????F?R??U"???GV?F???W'&?"&F????2F?R&F??F?R??GVFR?Bw&?WFV??&W7??6W2FV??GV?F?"?2?6R??6????F?G&6??bF?R?6?v??F???????V"F?7F?'F???2?V?f?7V??RF?RVffV7G2?bf??FW'2?F??W?W'2??6Rf&?F???2?bF?R6'&?W"??BV6??G&6?2?bF?R??6???r?6?v????U"6??V?BG&2?7V6???WG2??F?R6?v??F??g&????B???rFW&?G&?gB2vV??26??R6??'B?FW&???6?VF??r?F?R???GV?f&?F???2?WF??"3F?"WF?F?RFW7B???B?????'WB?B6???BG&6?&?"&?6?&G2G??6?w&?WFV????6?VFRFWfV???V?B?bfW'?f7Bf&?F???2&?fR?G2&W7??6R?2?&vR?V?&W"F?R4Eb?V7W&V?V?B???&W7??6R?6?????bw&??W2r7WW&???6VB??&?"&?6?&G2?2?fW"#FV6?????w????Vf7GW&FV??GV?F?"?F?Rv?FV&?Bv?FW"G&V?B?F?Rw&?WFV???V'2?bW?W&?V?6R??F?R??r7W?'B??B??GFW"?2??&RF?vV&?Rf&?F????2W7V??W?&W76VB4Eb??GW7G'??26?6?W2??&?WF??r76?7F???'&?v&?B??GFW"???v?2s?v?V?6V?V7F??rV?f?V?FW"?b?V??F?6R?&?"???G2%4TR?W&F??r?WGv?&??2F??V????G2f?"FV??g2?V?v??VW&??r??F?R?2g&??F?R????7FFRv?R?bG&FR??fg2&WGvVV?g&WVV?7??????f?"F?RG&V?B?Bf?V?F??r?V?&W"V??fW'6?G??B??4TR???&?WFW'2?F??V?7&?72F?R&?B???Bf?"?bfTU??&?"?2W?FV?g&??F?RvV?&v???vRF?W6RG&FR??fg2????G2v?f??r?V??&??W26?fRW?W&?V?6R??$b?BD?54?2??7F?GWFR?bFV6?????w??&?"?fW2????GW7G'?7F?F&G2&Rf?VR?fW"fW'??'&?rFW7B?B?V7W&V?V?BWV??V?B?F??F?vV?&v??B?2?7F?fRFVf??VB'?45DR?6&?V?'2?&?B?v??6??2??B6?v??f?6?B?&?.( ?2&W7??6?&??F?W2BfTU??V?&W"?bF?R45DR??BE42?UU$??TD?3P??