AN3218

Interferer waveforms

Doc ID 17543 Rev 2

3/6

Figure 1.

Comparison of spectra, 25 MHz span

It can be seen that the heavily filtered 15.4 signal generated by the signal generator is not

representative of either type of modulation technique, and therefore does not give a useful

measure of real performance.

At 10 MHz there is a difference between the two modulation methods of about 10 dB. This

means that the vector-modulated signal could show a better ACR if the receiver's own

rejection is high enough. However, quoted alternate channel measurements should still use

an ideal signal since a system designer cannot know what type of transmitter is used in the

interfering node(s).

Note that the standard specifies using an 802.15.4 signal of pseudo-random data for the

interferer. This is not the same as using a signal generator to generate an MSK signal with

pseudo-random chips, although the effect on ACR is small. The difference between random

MSK chips and random 15.4 symbols is the dip in the spectrum at 0 Hz offset.