Figure 1 shows a spectrum measurement performed with a high-end signal and spectrum analyzer, which no longer belongs to the newest generation and has an intermediate frequency of 404 MHz. The frequency difference between the input signal and the image-frequency signal is 808 MHz. With this 500 MHz bandwidth input signal, it is just still possible to test if it complies with the EIRP spectrum density mask according to ETSI TS 102 524 V1.1, by subtracting the reference measurement spectrum from that of the actual measurement. If the input signal had a bandwidth of 1 GHz, that would no longer be possible because the input signal and image-frequency signal would superimpose on each other. The influence of the image-frequency signal would strongly distort time domain analysis of the signal (I/Q data), where correction using a reference measurement is not possible.
Spectrum analysis: able to handle wideband-modulated signals
Modern signal and spectrum analyzers such as the R&S FSW equipped optional LO/IF connectors for external mixers have a major advantage compared to conventional instruments. With an intermediate frequency of 1.3 GHz, the analyzers have an image-free frequency range of 2.6 GHz. This makes it easy to measure the EIRP spectrum density mask of wideband-modulated signals, even if their bandwidth reaches into the GHz range. Together with the harmonic mixers from Rohde & Schwarz, e.g. the R&S FS-Z90 (60 GHz to 90 GHz), the achievable dynamic range is truly unique. The mixer has a typical conversion loss of 23 dB at 80 GHz, resulting in a displayed average noise level (DANL) of approximately –150 dBm/Hz for the complete test setup, including the R&S FSW. A 1 dB compression point of nominally –3 dBm results in a dynamic