SDR_Exciter

A MicroController based SDR IF

Introduction
After a joyfull discussion on building a SSB VHF tranceiver i got triggered again.
One of my first tranceivers actualy was a 2M transverter driven by a converted all mode CB radio.
Another quiet plessant rig was my 2M to 6M transverter somewhere in the late 80's.
These day's i've done lot of stuff using software defined radio.
Initialy GNU/Radio, later made my own SDR framework, to be followed by experiments based on MicroControllers and of FPGA's.
Anyhow, the discussion drove me into the idea of creating a SDR based multi mode exciter to be used for....
yeah i dunno.... how about a VHF radio capable for 50MHz and 70MHz.
I wonder where this road leads me to as most people only try shortwave.
Then again, my first SDR experiments somewhere in 2004 where at no less than 2.4GHz.

Hardware
Initialy i took a PIC32MX220F032D but i found out this CPU lacked some features really needed for my approach.
So i dropped that one, still here a image of the first experiment.

Initial experimental setup

Being wiser now i selected a PIC32MX440F128H installed on a Olimex Arduino board.
I do not use anything of the Arduino stack for this project, just use the hardware as a kind of breakout board.

Here is an image of my initial setup.

The same idea using another MicroController

I started only a day ago since i made this image, and currently i have 3 PWM outputs, playing a sine wave of which one is shifted 90' to test the quality of the cheapass hilbert transform function i created.

CPU Choice
Most people use ARM Microcontrollers for embedded SDR radio's.
I'm not in any way fond of ARM MPU but i do have a strong preference for PI32MX controllers.
Reasons for this are:
• One of the few 3v3 CPU's that can stand an awfull lot of rewrited while developping.
• MIPS 5 stage pipeline architecture, making them damm fast
• MIPS architecture for which all instructions are 5 clockcycles offering predictable executing time, reducing apperture errors.
• Challenging if you are like me stupid enough to try assembly on them
• No framework forced, although with newer CPU's MicroChip also tends this way.
• They are cool !

Software
I'm not using any kind of libraries, framework or equivalent crap
as i keep on noting SW bugs on cheapass SDR radio's that are i direct result of all kind of nonsens caused by not willing to read a datasheet, and not understandig how it is done.
It's a spare time project so time is no issue.

More to follow