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

Test ProceduresSMIQ5.3.5.4 Broadband NoiseTest assemblyTest methodConnect spectrum analyzer to RF socket of the SMIQ.Operate the spectrum analyzer in the CHANNEL POWER mode.Set SPAN to 400 kHz, channel bandwidth to 350 kHz, detector toSAMPLE, attenuator to LOW NOISE, and PLL bandwidth withCOUPLING/MAIN PLL BANDWIDTH to LOW. For reference levelmeasurement, set the center frequency of the analyzer to the testfrequency, set the reference level to the test level, and read thechannel power. Then measure the reference level by shifting thecenter frequency of the analyzer by the desired offset (for example5 MHz). The channel power now displayed must be converted to 1 Hzbandwidth and referred to the carrier power. By performing ameasurement without input level, the analyzer’s inherent noise can bedetermined and subtracted if necessary.Measurement Determine the channel power with the center frequency of theanalyzer set to the test frequency and note it down as P ref . Increase the center frequency by the offset (5 MHz). Inhibit the switching of the attenuator with REF RF ATTENMANUAL without entering a value so that the input mixer is notoverdriven. Lower the reference level of the analyzer by 20 dB, read the newchannel power P noise and note it down. Minimize the output level on the SMIQ by means of RF OFF, readthe channel power P res and note it down.Evaluation If the power P res is lower than P noise by more than 0.41 dB and lessthan 10 dB, the inherent noise power of the analyzer can besubtracted. To this effect, convert the two power values into mWaccording to the formula PmW = 10 (PdBm/10) , then subtract P res fromP noise . Reconvert the corrected power into dBm according to theformula PdBm = 10*log10(PmW). If the power P res is less than 0.41 dB below the power P noise , theanalyzer resolution is not sufficient for a precise measurement.The true result is in such case certainly more than 10 dB below themeasured value. If P res is more than 10 dB below P noise , P noise neednot be corrected since the noise component of the analyzer isnegligible. Convert the power P noise to 1 Hz bandwidth according to theformula P1Hz = Pch - (10*log10(channel bandwidth)).The difference between the (possibly corrected) power P noise indBm and the power P ref in dBm is the broadband noise floor indBc.Recommended test frequenciesRecommended test levelsSee Table 5-2, at least * frequencies.Pcw min with unmodulated carrier and Pvm min with vector modulation atfull-scale level (0.5 V DC at I or Q input)1125.5555.03 5.22E-9