Operating Manual R&S SMIQ - Volume 1 - Rohde & Schwarz

SMIQTest Procedures5.3.16 Digital Standards (Options)5.3.16.1 Adjacent-Channel Power Measurement with Higher Resolution5.3.16.1.1 Broadband SystemsEspecially in measurements using the LOW-ACP filter (option SMIQB47), results are influenced by theinherent noise components of the analyzer. The procedure described below allows the measurementlimit to be extended beyond that of standard settings. The adjacent-channel power measurements are made with the RF analyzer (Table 5-1, item 2)using the CHANNEL POWER marker function. To measure the channel power, set the CENTER FREQUENCY to the carrier frequency, SPAN toabout twice the symbol rate, POWER MEAS SETTING/CHANNEL BANDWIDTH to about 1.4 timesthe symbol rate (unless otherwise specified), TRACE/DETECTOR RMS, SWEEP/TIME MANUAL to1 s, REF LEVEL to approx. 3 to 5 dB below the PEP of the SMIQ, ATTEN AUTO LOW NOISE. Notedown the channel power P Chan .Note:The dynamic range of the FSIQ is at its maximum with reference levels close below a10 dB limit, for example -1 dB and 9 dBm with –11 dB. To measure the adjacent-channel power, detune the CENTER FREQUENCY by the channelspacing, set CHANNEL BANDWIDTH and SPAN (1.4 times the CHANNEL BANDWIDTH) anew ifthe adjacent-channel power is measured with a different bandwidth. To prevent a switchover of theanalyzer attenuator, activate REF/RF ATTEN MANUAL. Reduce the REF LEVEL by 20 dB (unlessotherwise specified). For some measurements the PLL bandwidth of the FSIQ must be setmanually. This is done under COUPLING/MAIN PLL BANDWIDTH. Read the adjacent-channelpower ACP. The measurement must be made for both sides (plus and minus the channel spacing);the worse value is the result to be taken. In critical cases, the inherent noise of the FSIQ must be determined and subtracted. To this end,press RF OFF on the SMIQ and read the inherent noise power PFSIQ from the FSIQ. If the inherentnoise power is below the previously measured power by more than 0.41 dB and less than 10 dB, theadjacent-channel power can be corrected as follows: P Corr = 10 *log10(10 (ACP/10) - 10 (PFSIQ/10) ) The relative adjacent-channel power in dBc is ACPR = P Chan – P Corr . If the inherent noise power is less than 0.41 dB below the previously measured power, the powermeasured is the inherent noise power of the FSIQ; the component contributed by the SMIQ cannotbe exactly determined, it is more than 10 dB below the measured value. If the inherent noise poweris more than 10 dB below the previously measured power, a correction is not necessary since thenoise component of the FSIQ is negligible. Since intermodulation products of the analyzer can be introduced especially in the first adjacentchannel, the measurement should be repeated with a 3 dB attenuator at the analyzer input at leaston preparing the test setup. The results must not be altered by this measurement.1125.5555.03 5.45E-9