Just thinking aloud here,
Over the past 20 years, the amateur radio scene has seen a disruptive change in hardware design brought about by software defined radio. Hams pioneered it in fact. Here's an article that introduced it to many of us https://sites.google.com/site/thesdrinstitute/A-Software-Defined-Radio-for-the-Masses
. No more superheterodyne circuitry.
The sdr principle is simple: On receive a small part of the radio spectrum (say 3.7-3.72 MHz) is mixed with an RF oscillator (say at 3.7MHz). After low-pass filtering the difference signal spans 0-8kHz or maybe as high as 0-192kHz. Actually two signals are produced, 90deg out of phase with each other using a Tayloe detector (Dan Tayloe perfected it). These two signals are digitised by a cheap stereo, low-noise 24bit sound card chip into two streams of integers, usually labelled I (in phase) and Q (quadrature).
From there on, the signal path is all digital until the sound output dac, amplifier and speaker. The platforms that hams have used range from multicore PCs, through RasPIs down to DSPIC33 chips. A pal of mine in northern England has developed an HF radio with the DSPIC33 - he can be heard most weeks chatting with other hams all over Europe. He gets good signal quality reports. He's also a keen cave explorer, and has developed 'cave radios' for surface-to-ground communications and for cave surveying. (VLF signals penetrate rock to a degree). He runs his radios at between 8k - 16ksamples/second - adequate for the 3kHz wide signals used on-air.
He's programmed the dsp on a 70MHz dspic33 in C, on a sample-by-sample basis - he doesn't process arrays of samples due to compute/memory constraints. The DSPIC is used to control the radio hardware as well - tuning, band change etc. He's recently switched to using a dual-core DSPIC and split the tasks. One core does the hardware control and the other the DSP. He still complains that the cpus are only 16 bit and that requires all sorts of maths tricks to avoid signal degradation. Quite a lot of original work and also looking back to the older dsp techniques for ideas - he's very clever to get so much out of that cpu.
So it begs the question: what could be achieved with a 200MHz 32 bit P2 with cordic engine and dsp instructions? The signal processing breaks down into a number of stages - maybe around six - for which the COGs would seem to be a natural fit, data being handshaked between the stages in a pipeline. Probably an external A/D would still be needed for receiver input because of very low noise requirement, but the P2s' internal converters could be used for mic input, speaker output and possibly transmit output (the latter then being mixed up to the required RF band by other circuitry). DSP sample rates might improve on the 16ksample/s that my pal achieved. 32bit arithmetic with 64 bit intermediate results would be much easier to manage. There might be enough processing time spare to do a spectrum display - always good for searching for signals.
Most of the DSP primitives would be assembly code for speed. Gluing the primitives together to make the complete radio - TAQOZ every time - forth is great for interactive prototyping. To provide stimuli and measure responses, the programming language LabView for Windows is fantastic and the Community edition is free for non-commercial use. It suits hardware engineers very well; like forth you get quick results. High speed serial link(s) could link P2 and PC during development to exercise the dsp in real-time. For a standalone radio, then there are plenty of small displays we know the propeller can drive and would make good front panels.
The latest SD radios use very high speed A/Ds to convert the whole
of the short wave band to a digital stream which is then processed by a large fpga. Both these devices are power hogs, expensive and a dog to develop - the fpga tools are very slow. Thus this technique is not the best for portable narrowband equipment, but great for high speed data and the intelligence community!
If we stick to the lower speed sdr technique, the P2 is more simple to program than most cpus and well suited for battery operation, 2-3W at most. Not forgetting it would save quite a few other parts too.
I'm looking forward to see how much 'radio' can be squeezed into the P2 - I'm sure it's more than people think. Any other radio heads - have you been thinking about this too?
Cheers, Bob G4BBY