Where is the Rx and Tx Image Rejection adjustment?
A. Operator manual image rejection adjustment is NOT required with a DDC base transceiver. The reason one has to deal with image rejection on QSD/QSE is because the IQ signal is in the analog domain and the two analog channels are always slightly different. The perfect quadrature relationship between IQ cannot be maintained since the I and Q analog channels will always be slightly different from each other – just the nature of having two different analog channels. PowerSDR from Flex deals with the image rejection using a sophisticated algorithm. In the DDC/DUC architecture you don’t have IQ in the analog domain, just a plain real signals. The IQ decimation all happens in the digital domain – since it’s all math, there’s no difference between the I and Q channel processing so there are no image issues. This is not to say it’s perfect … it’s only as perfect as the number of bits used in the processing and A/D and D/A channels and a properly constructed FPGA code base.
