What SA settings can I use during modulation BW measurements in ETSI?
For the Modulation Bandwidth measurement method ETSI says the following:
"The spectrum analyzer SHOULD be set to: peak detector function and max hold trace mode."
With applying these above SA settings the phase noise can cause compliance issues. In the 868 MHz frequency band the 1 MHz offset (-36 dBm/100 kHz) in case of high power (+27 dBm) Si446x radio boards, meanwhile the 6 MHz offset (-54 dBm limit under 862 MHz) in case of Si4010 crystal less operation can get close to the limit.
This is the real concern, because the exact wording of the standard says MAX HOLD *should* be used on the spectrum analyzer. This is not a requirement, but a suggestion, otherwise there would say *“shall be used”*. The standard calls for spurs as results of mixing, and suggests to use MAX HOLD to catch them during transmit bursts. BUT, it does not make sense to measure noise in MAX HOLD. Noise is measured using averaging (RMS detector and/or trace averaging). So an expert test house does this measurement in 2 steps. First in MAX HOLD, and 2nd using averaging (if no spurs are visible).
With applying trace averaging the phase noise level (of Si446x, Si4010) will be under the limits with nice margin.