Following on from last month's experiments with simple phasing receivers and SDR, we will take a closer look at some of the available PC-based SDR software. We will also have a go at building some good old-fashioned analogue phasing equipment.rnWhen most of the stages of a radio receiver or transmitter are implemented in software, it is possible to build a radio with very advanced features using very simple analogue hardware. Ideally, the only analogue circuitry employed would be limited to a low-pass filter to remove alias signals and a high performance ADC (analogue to digital converter). The RF signals would be sampled directly at the receiver front-end and converted to digital form. You can think of such a receiver as being equivalent to a PC sound card with a very, very high sampling rate and a maximum input frequency measured in MHz instead of kHz.
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