Uses for a software defined radio

I developed between 2004 and 2009. As such, it is not representative any more for all my SDR activities, which have continued since then, though mostly on the software side. Since summer uses for a software defined radio, I have been experimenting with the new way of building a radio receiver known as “software-defined radio”. Updated April 2013 What is Software-Defined Radio?

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Traditionally, radio receivers were built using analog hardware, like capacitors, coils and quartz crystals for filtering, and a diode as a detector. The local oscillator is simply a crystal oscillator at 4 times the desired receive frequency, followed by a two flip-flop circuit to divide the frequency by four and produce the 90 degrees phase difference between the two signals. Thus, in this example signals between 7080. PC is probably also a good idea. Connection to the PC using ethernet. The latter simply is a software implementation of what would be an IF filter, a product detector and a BFO in a hardware implementation: basically, an SSB or CW demodulator. Note the carrier and the sidebands on both sides of it.

At the top left is a preliminary version of the VCO. In a later version, it should cover 60 – 120 MHz. Update October 2005 Since the last update in February, much work has gone into developing an electronically tunable preselector. The purpose of this was to prevent noise from the digital part from entering into the analog part, but this is not very successful. In fact, it is unclear what route this noise takes, but it sure doesn’t seem to be blocked by this new shield.

Before continuing building, I’m now redesigning the software. It used to use just one FFT to go directly from the input signal to a spectrum with 50 Hz resolution. My computer however isn’t fast enough to do that at 2. D converters, FPGAs and 0603 SMD components. 5 mm grid of the IC pins is not a problem: “kitchen-table” etching techniques turn out to be good enough for producing 0.

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