The “External LO” block is use to add noise on the LO signal of 2GHz specified in the “ad9361_tx” block mask, while the “Ideal Source” complex sine signal of 2MHz (look under the mask) is the modified input to the modular found in the subsystem “ad9361_tx/ad9361_tx/RF_TX”. The noise skirt is specified in the “External LO” block, while the bandwidth of the signal is related to the “Step size”, Tstep, found in the “ad9361_tx/ad9361_tx/RF_TX/Configuration” block. The Configuration block is also use to specify the simulation frequencies.
The “ad9361_tx/ad9361_tx/RF_TX” has three Inport blocks. The blocks “Inport_I”(real part of complex baseband) and “Inport_Q”(imaginary part of complex baseband) specify that the complex sine signal resides on a DC carrier (Carrier frequency = 0). If the carrier frequency is not DC, then the complex baseband signal is handled as I+jQ. The “ad9361_tx/ad9361_tx/RF_TX/LO Signal” block specifies the LOFreq and the “ad9361_tx/ad9361_tx/RF_TX/Outport” block specifies that the desired output carrier frequency is ‘RF’. The output carrier frequency of interest should be DC+LO=LO=RF=2GHz. The original baseband signal, after system processing, will reside on this RF signal. However, a baseband signal is I=jQ where the carrier is implied but not shown.
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