Can you hear a radio transmission through a fan?
Answer: it’s possible.
So, here’s the deal. MacGyver needs to communicate with this kid on a nearby plane—but he doesn’t have the radio speaker turned on. How do you tell someone to turn on the speaker if they don’t turn on the speaker?
There are two parts to this answer. First, you need to build an AM radio transmitter. This isn’t too difficult—especially for MacGyver and all the stuff he has in the Phoenix jet. Here is a build similar to the one in the show.
Fine. But what about hearing it in a fan? The short answer is that the fan can act like a foxhole radio. Yes, that’s a real thing. It’s a type of radio that soldiers could build using some basic items. But the key to all of this is the diode. A diode is basically a one-way valve for electric current (I said “basically”—so, don’t freak out about that definition). Why do you need a diode? It’s because you can’t “hear” radio frequencies.
Let’s look at AM radios (because FM is a bit more complicated). AM radio stations broadcast at different frequencies for different channels. These frequencies range from 500 kHz to about 1500 kHz. But if you just convert these electromagnetic waves into sound, you wouldn’t hear anything. Humans can only detect frequencies up to about 20 kHz. So, how do you fix this?
The answer is amplitude modulation (the A and M of AM radio). Here is an example of how this would work. Suppose I have a radio frequency of 3333 Hz (I just mostly randomly picked that value to make a pretty graph). Imagine this radio signal is just a cosine function that oscillates with that frequency. Now suppose that I constantly change the amplitude of this radio signal. The amplitude ALSO changes with some frequency—let’s say this amplitude frequency is 150 Hz (typical human voice frequency). Here’s what that would look like (here is the code if you want it).
But this won’t work. You can’t “hear” the 150 Hz signal—the problem is that the average of the AM signal is zero. It goes up as much as it goes down. It won’t work. That’s where you need a diode. This diode only allows the receiving signal to go “one way”. Here’s what that same AM signal looks like when you put a diode in.
Now for that diode. You could use a diode—or an LED light (which is a diode). Old crystal radios use a crystal mineral. If you don’t have that, you could use a pencil with a razor blade. Apparently, this kind of connection acts like a diode. Oh, you could also do this with the metal connection in the brushes of an electric motor—like in a fan.
Here is a story about a guy that thinks he’s crazy because he hears voices in his fan. I guess it’s true. Also, there is the famous (but maybe not true) story of Lucille Ball hearing Japanese spy radios through the fillings in her teeth. Here is the Snopes link for that.
One last comment. If you think “oh, this is awesome—I’m going to go listen to a radio station with my fan.” Nope. It’s probably not going to happen. You need a fairly strong AM radio signal that is tuned to your untunable fan. On top of that—the brushes in the motor of the fan have to be JUST RIGHT for it to work. It’s still plausible.
A defibrillator uses electrical currents to do something with the electrical nerve signals to the heart. I guess they can trick the heart into restarting if it has stopped. Fine—but how do you build one (note: don’t build one)?
Of course as with most things (especially dealing with living humans) this can get tricky. You want to run electrical current through the heart area, but not too high. Also, it’s probably best to have an alternating current—it’s complicated.
The simplest (and oldest) designs use a DC battery along with an inductor and a capacitor to make an oscillating electric current. MacGyver should be able to use the DC power from the plane as the “battery”. If you want to start with a higher voltage, you could charge up some capacitors and then reconnect them in series to pretty much get whatever voltage you want. The inductor shouldn’t be too hard to find either.
Electromagnets are real. I guess you already knew that. The basic idea is that an electric current creates a magnetic field. If you make the wire into a coil, the magnetic field due to each loop will add together to make an even stronger overall field. Oh, more current is better.
But would this work in real life? Of course it depends on many things. The most important thing is the current. How much electrical current could you get out of an airplane?
I’ll be honest—calculating the current needed for an electromagnet is really tough. The magnetic force depends on the type of material being attracted (probably steel), the distance, the size of the coil, and the current. But still, I think you could get at least something like 1000 Newtons (a little bit more than the weight of a person). This might be enough to help a small airplane stick to the top of a truck. It’s plausible.
But let me just leave you with the BEST use of an electromagnet. Allen Pan made this AWESOME version of Thor’s hammer. It uses an electromagnet and a thumb sensor so that only Allen (who is obviously worthy) can pick it up.