terry.lynch wrote: > Philip, I think your idea of using the microchip dsp is really neat!.I > hope it works out for you.Please let us know how you get on.Best > wishes, terry lynch.
Well, it's not just the Microchip dsPIC.. it's the dsPIC and a PIC18F4550 to do USB interfacing and handle the front-panel controls. One chip decodes, the other talks to the human at the keyboard. The plan is to do AM/SSB in software on the DSP, but have a bypass option that disables the FFT processor and feeds the raw audio straight into the 4550. RF-wise, my plan is to hack together a dual-conversion tuner with IF1=10.7MHz and IF2=455kHz, then downconvert the 455kHz IF to 12kHz for the DSP. Technically I suppose that makes it a triple-conversion receiver, but who's counting? :) I'm dead-set on using an Analog Devices DDS synth for the tuning control. More specifically, an AD9913 - 1.8V, low power, and good to 100MHz. I'm planning to rig it to a 10MHz reference clock (internal/external switchable, just in case I decide to build a GPS-locked OCXO frequency source in the future) and boost that to 200MHz using the onboard PLL. So over the 0-30MHz SW range, that's a worst case of 6.6-recurring steps per cycle. Lowpass that at 30MHz and the harmonics fade into the background fuzz. I'm planning to use a couple of salvaged 10.7MHz and 455kHz ceramic filters I 'liberated' from a pair of Superdrug "half price" SW/AM/FM radios (which are awful on SW, reasonable on AM, and fairly good on FM). By that I mean, they suffer terribly from image response on SW and AM... This is all up in the air at the moment and likely to change at short notice, but it's a little bit of fun that should help keep me from going mad from boredom :) -- Phil. | (\_/) This is Bunny. Copy and paste Bunny [EMAIL PROTECTED] | (='.'=) into your signature to help him gain http://www.philpem.me.uk/ | (")_(") world domination.
