Actual example of AGC in SDR hardware In the CIAO H101 block diagram the RF Input from the antenna comes in via a dual antenna switch (selectable antenna inputs) to a LNA or low noise amplifier and is split off from the LNA to two mixers with the DDS LO IN between them. The mixer I/Q outputs each go to their own AGC control and then to their individual Low Pass Filters then to the sound card. (LNA: This means there is a analog front end or RF amplifer stage ahead of the QSD section.). So there are AGC Controls in the hardware one for the I and the Q. And so there is AGC control in the software for the audio as well as in the hardware and this primarily is advantagous for the AM Synchronous mode I understand. And both AGC controls work off of the tuned to signal in the software (I believe) and so the AGC in the hardware is not sampled and provided for in the hardware which would not be desireable there. Software derived then means that a strong adjacent signal will not over ride the AGC in the hardware. This scenario was not foreseen in the discussions we had here. I suspect however that the hardware AGC does work in the other modes as well but is not acting in the synchronous sideband manner, meaning the individual I and Q AGC would be slaved to track each other. This also makes me wonder more about the idea of using seperate I and Q noise blankers in the hardware? But I know of an example of that already in software. I have seen noise appear only on one sideband across all of the AM station signals and on the same side band in each, and this then meant to me it was a phased noise: and this destroyed the signals and the remedy was to switch from AM to the unaffected side band. The software that has dual I and Q noise blankers (SharpDSP Mini Console) unfortunately does not have a spectrum display to see and study this effect when it ever occurs again to see if the dual noise blankers will remedy this. I thus can not test that idea if I can not see it.
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