the following statement is taken from the telemetry standard IRIG Standard 106-11:

The RF signal is typically generated by filtering the baseband non-return-to-zero-level (NRZ-L) signal and then frequency modulating a voltage-controlled oscillator (VCO). The optimum peak deviation is 0.35 times the bit rate and a good choice for a premodulation filter is a multi-pole linear phase filter with bandwidth equal to 0.7 times the bit rate.

Could anyone explain what “optimum peak deviation” means? Is it a parameter of filter? Are such constraints difficult to achieve?