I am accessing the Internet, downloading PDFs, and much more, but how?
The servers are far away, but how do I download data if it is far from my computer? I can watch football matches live on television, because of radio & TV waves, but what waves are responsible for Youtube live videos, for example?
Internet signals are mostly transported via cables. Some satellite links exist but they are less common. So we have cables and signals within them. Some cables are made of conducting metals others are glass fibers. The signals in the glass cables do not have the same properties as the ones in the metal wires, they are basically light that is sent through a dedicated path. So then we have the metal cables and signals within them. And indeed signals in metal cables have the same properties as radio waves. Whether the wave in the cable contains digital or analog data does not really matter, cables transport waves and waves are inherently analog. Basically you can model a cable with two endpoints as two antennas that are connected to each other. For an antenna the ground serves as one wire - the mass - and the metal piece pointing into the sky is the other wire. So first you replace the ground with an actual wire and connect the two antennas that way, then you connect the two metal ends that were pointing to the sky, and voila you have a cable. The thing with a cable is that it can transport signals of very low frequency as well as high frequency. Antennas are only suited for high frequency waves, the so called radio waves.
The waves that carry signals for the internet are the same kind of waves used for radio and TV. It is also the same kind of wave as for visible light, x-rays, and gamma rays. The difference between these waves is frequency and wavelength. Radio and TV use waves longer, lower frequency waves than you can see. X-rays and gamma rays are shorter and higher frequency.
Another difference is that light often travels through vacuum. But it also can travels through some substances. Air and glass are good examples. Light can be reflected from mirrors.
Transparency is dependent on frequency. Low frequency waves can travel through some substances that are opaque to light. For example, a garage door opener emits a radio signal that goes through the garage door to a sensor in the garage.
Cables that carry the internet signals are coaxial. They have a central metal wire and an outer metal sheath. These act like a mirror. The area in the middle is transparent at the frequency of the signals. So the cable is a long transparent tube with mirrors. Though at long wavelengths, it is better to treat the signal as a wave than as rays.
Some internet signals are wireless. These are carried by radio waves without a cable.
When you receive your radio-wave TV signal over the air using an antenna, the electro-magnetic wave is converted to electrical AC current that includes the same frequencies as the radio-wave. This antenna captures the radio (aka TV) electromagnetic wave via the Electric field strength part of the electromagnetic wave.
The Antenna is connected to your TV set via the transmission line which could either be twin-lead or coaxial cable. More modern implementations likely use coaxial cable. The electromagnetic signal derived from the actual RF wave captured by the antenna is now moving through the coaxial cable at slightly slower speed. The speed of the wave is usually around 90 percent or so of light-speed due to the dielectric losses in the cable (twin lead offers a faster speed due to less losses).
So, when the signal is in the transmission line, it is just like an Internet signal that comes over cable or phone line. It is a modulated AC (alternating current) signal. With all TV in the US today and many other places, this is a digital modulated signal rather than the old style analog signal -- however, the signal itself moving through the wire is an analog voltage changing signal.
The transmission side of the TV or radio signal is also an antenna. Thus, the electromagnetic wave travels through space (atmosphere) from transmission antenna to receiving antenna. But, the electronics on the transmitting side also uses transmission line (usually coaxial cables) to deliver the signal to the transmitting antenna.
Therefore, if you were to extend that transmitting transmission line to your home and connect directly to your receiving transmission line (probably reduce power as well) then you have a system very much like the Internet connected via wires and switches (aka Routers).
So, not that much difference between the Internet wires based signaling system and the use of space born electromagnetic waves.
Internet fiber optic cables transmit via E-M waves in the light domain, instead of the radio domain. The frequency of the light is typically around 1500 - 1600 nm. A single fiber can also carry multiple frequencies (wavelength multiplexing). These different wavelengths are about 0.8 nm apart.
Although some radio waves might be used in your downloads (esp. if you have a wifi connection) it is primarily light waves in the 1500-1600 nm range.
For reference, the longest VISIBLE light is about 780 nm (dark red), so these would be infrared wavelengths of light that are sent through the fiber optic cables.
Most if not all commercial and government networks use DWDM transport fiber optic systems that transmit and receive signals at 1310nm, 1550nm, or 1625nm across the globe. At certain points on the network these signals are broken down or demux’ed down into multiple frequencies of light. The internet companies can then assign or lease each frequency out to each customer as a circuit depending on the A and Z locations the customer requires. This is how Youtube, Facebook, Amazon, and others provide access to their services globally. These companies spend million annually for these circuits and the internet companies like Lumen Technologies, Verizon, and AT&T spend millions of dollars, constantly building to keep up with demand. SpaceX is the latest company to get into the business of internet access. SpaceX receives 100 gigabyte per second circuits via Lumen fiber optic network then is transmitted up to SpaceX satellites to link to all of their customers on the ground.
