Is it possible to do simple wireless on an Arduino, digital, or analog (SDR)? I would like to hook one pin to an antenna (or piece of wire) and generate signals with simple modulations (analog or digital).
here there's a nice tutorial on how to obtain it.
Basically it sets the registers so that a pin outputs a PWM signal at 800 kHz and then modulates that signal in code by just switching the pin and off (pinMode set to INPUT or OUTPUT). If you plug a cable (20 cm and on) to pin 8, and tune your radio to 800Khz you'll hear some noise going on and off.
If you read down the forum you'll see people suggesting how to actually send tones, by putting a very small delay (delay(1)) between the on/off of the pin.
In this link they guys have ogn further and they even implemented a morse code library.
Now I am trying to figure out a way to do the same for a receiver.
Based off of what you have said, the simplest way to achieve what you want to do with your Arduino would be to use a WiFi shield, and setup the Arduino to function as a web server. I have included two links: the first link shows you Arduino's sponsored WiFi shield and explains the basics of how to use it. The second link addresses your question of using the Arduino+WiFi shield to generate WiFi signals, by setting it up as a web server. Both links contain sample codes from Arduino that you can copy and paste. Assuming that you are using the native Arduino software, you can also go to: File > Examples > WiFi > WiFiWebServer, and the same code from the Arduino websites that I listed will be there for you to use.
Personally, I would always recommend that whenever you want to accomplish a certain task, such as WiFi signal generation, displaying characters on a LCD, or anything else, you search for a shield to use for that application. Shields always make life extremely easier. I hope this helps. :)