My foxhole radio
blog.jgc.org
blog.jgc.org
Edit: I answered the wrong question here, thought he was talking about the coat hanger I used in the crystal radio set. In the case of the WiFi antenna it matters a lot!
Here's a site with a few different wifi antenna designs and some antenna modeling: http://www.lincomatic.com/wireless/homebrewant.html
This site has a calculator for cantenna dimensions: http://www.wikarekare.org/Antenna/WaveguideCan.html
My mistake for misinterpreting the question.
Have you looked into creating an earpiece/speaker? it's the "weak link" in such a basic setup.. always wondered if something could be cobbled together.
So you need to filter out the carrier part of the signal. Diode only allows current to flow one direction, and the rest of circuit allows it to discharge slowly (it has some capacity).
When there is unmoduled carrier wave (silence on radio), there is balance between the current that flows thoruhgt diode, and the current of discharge, so the voltage on speaker is more or less constant (probably not on 0 level, but it doesn't matter).
When carrier wave is modulated to half the amplitude, speakers gets less the voltage.
So speakers vibrate with voice wave frequency, not carrier wave frequency, so you can hear the voice.
Imagine you want to measure the daily sea level, and it's very windy (big waves). You can't just measure it once a day, because depending on the moment you'll measure high or low level of wave, and you want the average level. So you make a container that is filled by waves throught one-way pipe, and you drill small hole in the bottom of that container, so it leaks at a constant rate. When you tune the size of hole in the bottom, and the size of one-way pipe correctly, you can measure level of water in this container, and it will be proportional to the average level of water in the sea.
You can even make an oscillator from some of these negative resistance materials by just biasing the crystal with the right DC voltage and connecting a parallel LC tuned circuit. The basis for a simple transmitter!
OR you can use the high impedance earpiece form an old telephone instead of a crystal earpiece which will give a fantastic, clear and loud output.
My grandfather used to put his "cans" from his crystal set in a pudding bowl and it acted like a speaker -- several people gathered around could hear it at the same time.
A 300pf variable capacitor across the coil will also give you quite effective tuning.
http://www.crystalradio.net/crystalsets/hassell/index.shtml
Newpaper will be 'fun' to work with as its moisture content will vary with environmental conditions, making its dielectric constant not very..erm..constant - unless you impregnate it with wax or a lacquer.
(Made plenty of crystal sets during my teen years in the mid 70s-80s)
I have a "crystal" radio (uses a modern diode) all built on a paper towel tube. The coil is wound on the tube like usual but at the other end of the tube there's also a layer of foil and a smaller tube with a layer of foil that slides inside that to make a variable capacitor.
Also, I find that inserting a ferrite rod into the coil (or winding the coil around the ferrite rod to begin with) makes tuning much more effective (sharper) and makes the audio signal much stronger. A steel or iron 6" nail also works if you want to dispense with the ferrite rod.
I made a single transistor regenerative set next and because the local BBC signal was so powerful I literally didn't even need an antenna at all!
Another single transistor was all that was required to drive a speaker loud and clear.
The high value resistor in parallel with the earpiece provides a working load for the circuit. Without it the audio signal is largely being shunted by the large internal capacitance of the crystal earpiece.
The resistor is not required if using a high impedance moving coil or moving iron earpiece such as that from an old telephone.
Trust me, if using a crystal earpiece the resistor makes a big difference.