I've made and messed with a lot of stuff. Not only radio, but other electronics as well. Here are some of the more interesting ones.
Firstly, an AFSK demodulator that takes an audio signal made up of tones signifying 0 and 1. I don't have a schematic for this, but here's a picture of it in operation:
It's not a great photo, but you can see on the oscilloscope the 0 and 1 output square waves (when they're both low, it's a space between bytes). And you can see the circuit and my walkman hooked up to it. I don't have a record of it, but I also wrote a program for the Arduino that decoded ASCII from this input.
I have no photos or anything to go with this, but this circuit from aaroncake.net was something I played around with a whole lot when I first started out. I learned a lot from it. The whole site is pretty cool, and there's a giant database of various circuit schematics. You should check it out.
More recently I've been experimenting with AM transmitters/receivers. It's a lot easier than FM to modulate and (especially) demodulate. I've been mostly using frequencies around 27MHz, because that's an ISM band. I do realize that there are no unlicensed bands in Canada, but until I get an Advanced ham radio license, it'll have to do. Besides, it's so low power that I can barely pick it up from inside the house, let alone from a distance. And I don't yet know how to actually increase the power output, because RF is black magic and I still can't even wrap my head around how current flows in an antenna when there is no closed circuit. Anyway, I've got some schematics here:
Those are the latest schematics. If you're an experienced electrical engineer, or even an inexperienced one, you might look at those and think "Wow, this guy doesn't have a clue what he's doing". And you'd probably be right; I have no idea what I'm doing. But I'm trying to learn! That's what this is all about.
So, with these I have managed to transmit an SSTV image from one room to another, with rather good results:
That's a screenshot of the receiving end. The physical setup was, for lack of a better description, really ghetto. I unfortunately don't have a photo, but the transmitting end was a breadboard hooked up to a power supply with a long piece of wire attached to the final stage. The receiving end was also a breadboard, sitting on my desk, using a USB cable from a broken mouse as an antenna. Again, I have no clue how antennas work and this seemed to do well enough.
I also managed to blink the LED on an arduino remotely with these circuits. I transmitted an audio tone, and used a comparator on the receiver to decide when the tone was there and when it wasn't. This worked okay except the whole thing is just so god damn temperamental that the slightest disturbance in the force or whatever would it from functioning.
And I'm not even exaggerating. So much as standing too close to either of the circuits, moving either of the antennas, or even touching something electronic/grounded in the same room as either of them (seriously, I'm not joking), would upset the circuits and they'd need a moment to settle down again. I suspect a problem with the grounding, and I also don't know how that works so I'll need to read up a bit more before I try this again, since I think I've gotten about as far as I can without really understanding how radio works.