Patent ID: 7450633

Claim:
A digital line tester comprising: a wander generator for generating a clock signal having wander which satisfies a defined time deviation characteristic; a transmission unit for sending a digital signal synchronized with the clock signal output from said wander generator to a digital line under testing; a reception unit for receiving the digital signal returned from said digital line under testing and restoring a clock signal of the received digital signal; an error measuring unit for measuring errors in the digital signal received by said reception unit; a time deviation measuring unit for measuring a time deviation characteristic of the clock signal restored by said reception unit; a display device; and display control means for displaying a result of measurements of said error measuring unit and the time deviation characteristic measured by said time deviation measuring unit on said display unit in such a manner that it can be compared with the defined time deviation characteristic, wherein said wander generator comprises: center frequency information setting means for setting data for determining a center frequency of the clock signal; characteristic information setting means for setting characteristic information of the defined time deviation characteristic; a fluctuating signal sequence generator unit for generating a fluctuating signal sequence having a power spectrum density distribution characteristic of frequency fluctuations corresponding to the defined time deviation characteristic based on the characteristic information set by said characteristic information setting means; an adder for adding the data set by said center frequency information setting means to the fluctuating signal sequence output from said fluctuating signal sequence generator unit; a direct digital synthesizer for outputting a frequency signal corresponding to an output of said adder; and a clock signal output circuit for waveform shaping an output signal of said direct digital synthesizer to output a clock signal; wherein said fluctuating signal sequence generator unit comprises: noise generating means for generating a white noise signal based on a pseudo random signal: impulse response processing means for calculating an impulse response of a transfer function for approximating a power spectrum of the white noise signal output from said noise generating means to the power spectrum density distribution characteristic of the frequency fluctuations based on the characteristic information set by said characteristic information setting means; and convolution processing means for convoluting a result of the calculation by said impulse response processing means with the white noise signal output from the noise generating means to generate the fluctuating signal sequence having the power spectrum density distribution characteristic of the frequency fluctuations.