It depends on the strike and what you mean by protection. It's a safe bet that it won't work in many cases because it's not grounded.
There are different interpretations I can think of for this claim, as lightning surges come in different ways, for example:
- A lightning strikes your TV antenna or home directly
- A lightning hits the grid creating a much minor surge
In the first case, you definitely need more protection than the second. Tying knots in either the coaxial or the power cord will not make your TV protected against picking up lightning from the antenna or the house itself.
A lightning contains a lot of energy. When a lightning hits a TV antenna, that energy has to go somewhere. If your TV is attached to the antenna, it goes through it and then to the ground. Whether there are knots or not, energy is conserved and your TV is fried.
Dr Bob Howlett, Reader in Electrical and Electronic Engineering, University of Brighton:
Whether you plug your television in or not when there’s lightning around – it’s an interesting question. I think it’s one of those questions where the answer really is, it doesn’t make too much difference.
-- Lightning on TV
Clearly if unplugging a TV set doesn't make a difference, then tying a knot won't either.
Diverting energy to ground is the most important form of protection and this is obtained by grounding your equipment and your house properly, and installing a lightning rod.
Can we create an effective minor surge protector by tying knots in a cable?
The answer is that it probably won't work -- again, commercial surge protectors work by sending the extra current to the ground instead than your TV. Knotting a cable does not connect it to the ground.
They work by having a gap of air between line and ground. When a voltage goes over a specific level, the gap is filled with a spark which sends energy to the ground, short circuiting. Some versions can be directly connected to ground.
Another kind of spark gaps, but filled with a specific gas for better performance.
Metal Oxide Varistor is a voltage dependent resistor
- At low voltages it is open circuit (megohms)
- At some specified higher voltage, the resistance falls to a low value (a few ohms or less)
While of course this is a general overview of how surge protection actually works, it doesn't prove that knotting a cable doesn't work, but it shows that it's unlikely to work because it's not grounded.
Sources (they are the slides I'm summarizing here):