The main reason for interest in the PRTS for frequency response measure­ments is that the signal discriminates against nonlinear effects (it is anti­symmetric). Because several binary signals also have this property, they are preferred over the PRTS for future applications since the practical problems of inputting a three-level signal into a system are often significantly greater than problems with a two-level signal. Nevertheless, there has been some interest in the PRTS signal, and a discussion of its characteristics is included here.

f See the literature (32, 38, 49, 50, 56-61).

2. The power spectrum becomes flatter as Z increases, as with the PRBS and n sequence.

3. The absolute magnitude of the harmonics decreases as Z increases, as with the PRBS and n sequence. Again, the same bandwidth relations (see Section 2.12) apply.

4. The PRTS is antisymmetric.

The PRTS can be generated using a digital shift register with modulo-3 adder feedback. Signals can be generated for Z = 3" — 1 for integer values of n. Table 3.3 gives feedback connections that provide PRTS signals. Figure 3.10 shows two cycles of a PRTS signal (Z = 8). It should be noted

that while construction of a PRBS generator is simple and requires only the use of standard digital logic components, no comparable components are available for ternary logic. Thus the algorithm for PRTS generation is useful for implementation with a digital computer, but not as a basis for construct­ing a simple signal generator.