Back in the 20th century, putting tin foil on the end of an antenna was believed to improve reception. Results could be questionable, and for most people it didn’t work very well. Today’s antennas are more sophisticated so you could actually be hurting your chances of a strong signal by doing this.
Let’s back up a little and explain why this might have worked.
A lot of people think of an antenna like a net, or like flypaper. The bigger it is, the more likely you’ll receive something. That’s sort of true, but mostly not. Antennas actually need to be a specific length in order to receiver specific signals. Generally this is a fraction of the actual wavelength of the signal. It’s common to use 1/4 of the wavelength because it’s a fairly manageable number. Antennas also need to be parallel to the signals they’re receiving, meaning that the best placement for “rabbit ears” isn’t the typical “V”, it’s flat like this:
When you adjust a “rabbit ears” type antenna what you are really doing is changing the amount of the antenna that is actually parallel to the signal and therefore it’s like you’re changing the length of the antenna. When you add a flag made of foil to the antenna, you’re also changing its shape and sometimes, just accidentally, you can do it in a way that improves reception.
Of course, the “rabbit ears” type antenna is rarely seen anymore, because it was designed primarily for indoor VHF reception, and most stations today are UHF. UHF broadcasts use smaller waves and as waves get smaller, it becomes possible to use one antenna for a larger group of frequencies. That’s why today’s antennas are smaller and simpler, often consisting of a single loop or X-shaped element. Putting foil on one of these will usually simply make them worse.
So, keep the foil on hand for holiday dinners, but you won’t need it to watch TV any more.