4-WIRE DDS Disturbers Near-End Crosstalk Calculation

T1 disturber model from T1E1.4/95-007R2, Annex B (p142), modified for DDS AMI, verified in lab,

              ;in KHz

     ;-3 dB point of the first-order LPF for TX shaping in KHz

       ;-3dB point of the transformer modeled as a single-order HLP

        ;f is in KHz

             ;A is the TR62310 driving pulse amplitude in Table 9.4-1

PSD (dBm/Hz) of a DDS Disturber vs f (KHz)

        ;f is in KHz

               ;n = number of DDS NEXT disturbers (1, ... , 23)

PSD (dBm/Hz) of DDS Disturber NEXT vs f (KHz)

Low-frequency integrated DDS NEXT power (spot power for df = 1 Hz) (dBm) f must be < 20 KHz for this model:

High-frequency integrated DDS NEXT power (spot power for df = 1 Hz) (dBm) f must be > 20 KHz for this model:

Total power (dBm) is:

Comparison of DDS spectrum at various OCU (loop data) rates:

        ;f is in KHz

PSD (dBm/Hz) of Various DDS Disturbers vs f (KHz)

Conclusions: From 4 KHz to nearly 20 KHz, 19.2K bps DDS has the greatest PSD (note that 19.2K bps DDS was first defined in the August 1993 version of TR62310). Beyond 20 KHz, 56K and 72 K bps DDS contain more energy than any subrate, and (except for very narrow regions) at least 20 dB more power than the subrates 12.8K bps and lower (where additional band reject filters are specified, see note below).

NOTE: If OCU rates of 2.4, 3.2, 4.8, 9.6, or 12.8 Kbps present a high PSD in the 24 to 32 KHz or 72 to 80 KHz band, TR62310 specifies additional filtering (up to 17 dB in the 24 to 32 KHz band, and up to 9 dB in the 72 to 80 KHz band) for these OCU rates. This additional filtering is not included above.

PSD (dBm/Hz) of Various DDS Disturbers NEXT vs f (KHz)