TV Has Changed A Lot

That's quite an understatement. But in this explainer, I'll focus on one specific aspect of how TV has changed -- and that is how OTA (Over The Air) digital TV works today compared to before.

If you want to take a deep dive into all things TV, then here's some further reading: TV Today, Beyond Socket TV, Cutting the Cord.

I try to keep my explainers shorter than my full articles and focus on one specific aspect of a thing. So in keeping with that spirit, I'll just lay out some helpful facts about OTA broadcasts and their pros and cons.

If you want a deeper understanding of how analog and digital OTA works then you can continue past the simple explainer that's coming up next.

The Simple Explainer

Most people watch TV via streaming or cable TV. But even today's TVs can receive broadcasts over the air. But like any other wireless system that suffers from the intrinsic complexities of wireless, OTA TV is no different.

Signal quality is affected by many things: 1) Distance to transmission towers, 2) Environmental obstruction (buildings and terrain topography), 3) Bad weather (heavy rain and/or lightning), 4) Radio frequency interference from other devices, 5) Multipath issues (when reflected signals arrive slightly later), and numerous other causes.

With today's digital over the air broadcasts, a poor quality signal can manifest itself in these ways:

• Pixilation: Numerous square blocks that aren't fully detailed
• Motion smearing: Fast moving action leaving a trail of previous frame artifacts visible
• Stuttering audio or dropouts
• Audio that sounds "robotic" or you hear strange digital "brap"-like noises
• In severe signal loss, a black screen and/or no sound

Your options to cure are rather limited. If you are farther away from the transmitter, have a lot of tree cover, or if your exact locale is situated topographically in a bowl or low parcel of land, then raising the antenna could well fix that. The amount of elevation is highly dependent on local conditions and would require some experimentation. Honestly, this is probably your best and only fix.

Signal amplifiers might work, too, depending on what exactly is contributing to poor signal quality. If it's just due to attenuation from distance but otherwise clean then an amplifier may help. But if quality issues are due to radio interference or signal multipath issues, amplification will not help.

RFI (Radio Frequency Interference) can make amplification less likely to work. But that is a whole separate thing that I won't get into here.

It's also possible that nothing will fix your particular problem. That's one reason why terrestrial OTA TV broadcasting is seldom used compared to wired methods.

So that's your quick answer. See you later!

Or... if you are interested in why, proceed onward...

Nerd Alert!

In the old days before cable TV, people watched exclusively OTA broadcasts. Those broadcasts originated from tall antenna towers that were in your area, usually within a maximum distance of 25 to 40 miles, give or take, depending on how powerful they were and the topography.

Signals were received by either indoor "rabbit ears" antenna sitting atop a large boxy TV set, or better, a mast-mounted antenna on the roof with a cable that ran down to the TV set -- and a lightning arrestor if you knew what was good for you.

TV transmissions in those days were analog. Briefly, analog (in this context) means the content (TV show) being delivered is encoded on the transmitted signal by carefully altering the signal itself. That is, by modulating certain characteristics of the waveform such as amplitude and frequency.

Analog transmissions are generally more forgiving when conditions aren't ideal, such as the transmitter being far away or path obstructions such as buildings and trees. You might see some snow or static on the screen. Audio usually fared better because sound is less demanding than video when being transmitted and due to the way audio is encoded (FM rather than AM).

But that was then. Analog TV broadcasts in most developed countries is dead today. Now it's all digital.

Here's a simple analogy to help describe how analog and digital transmission is different but yet ultimately achieves the same result.

Analog

Imagine you and a friend are having a conversation. When you speak, your vocal chords are modulating the content (words) onto a pressure waveform. That waveform is transmitted to the other person via air molecules. In this case, it's a sound wave, not a radio wave, but the principle is the same. Your friend's ears hear the sound and decodes the modulated signal.

Digital

With digital transmission, the content is transmitted in a fundamentally different way. Instead of directly encoding the content onto the waveform, it is symbolized by converting to a series of 1's and 0's -- and then that is what's encoded onto the waveform.

Again, you and a friend are having a conversation. But instead of using actual spoken words, you are "speaking" by making a beeping sound with your voice. But not just any old random beep beep, like a backup alarm on a truck. Instead, you are using Morse Code for your beeping. As you might remember, Morse Code is communicating by using short and long beeps or, as we might say, dots and dashes. Again, this is using symbols to represent content.

Instead of saying "Hello" by enunciating its phonemes (heh-LOH), you would say "hello" by making a monotone "beeping" sound. In Morse Code, a dot is "beep" and a dash is "beeeeeep". (same sound, just a little bit longer -- 3x longer to be technically correct)

You could also think of the dot as a digital 0 and the dash as a digital 1.

So "hello", sent in Morse Code, would go like this. Each letter has a brief silence after it to mark the end of the letter.

H= "beep-beep-beep-beep" or "0000" (then a brief silence)

E= "beep" or "0" (then a brief silence)

L= "beep-beeeeeep-beep-beep" or "0100" (then a brief silence)

L= "beep-beeeeeep-beep-beep" or "0100" (then a brief silence)

O= "beeeeeep-beeeeeep-beeeeeep" or "111" (then a brief silence)

n.b. Morse Code does not use binary 0's and 1's! This is just an allusion to illustrate these two things (dots/dashes and 0s/1s) are serving a similar function.

Do you see what's happening here?

You have digitally communicated the word "hello" using Morse Code. Because the content was symbolically (digitally) represented, then it doesn't matter what audible sound you make as long as you can make two different sounds.

Instead of making the "beep" or "beeeeeep" sound, you could just have easily said "0" and "1" instead. As long as you followed the rules of Morse Code, your partner will understand (assuming, of course, they know Morse Code).

I know that was a bit laborious. But understanding the fundamental difference between analog and digital encoding is interesting and useful to knowing how digital TV differs from analog TV of yesteryear. Not just TVs, but the nature of how all digital systems differ from their analog brethren.

The digitalization and symbolization of data also means we can include error correcting measures. Error detection and correction is core to digital transmission and is what makes it possible to transmit a perfect copy of the source.

Practical Advantages to Digital

As I said farther up, analog transmission is more forgiving as signal quality declines. The quality decline you see and hear on a TV set is more or less linear with the decline in signal. Not exactly so, but not far off, either. And because of the nature of analog, error correction really isn't possible.

But digital transmission, on the other hand, have very different failure modes. For digital TV broadcasts, there are "Forward Error Correction" codes added to the content data packet before transmission. These FEC codes can help your TV reconstruct data that was corrupted or went missing during flight resulting in an error-free display.

If the transmitted packet is corrupted badly enough then you'll notice artifacts on the screen and may hear some weird noises. That should autocorrect when the next packet arrives, assuming it wasn't similarly corrupted.

There are different levels and kinds of reconstructive FEC codes that be be applied. Alas, explaining all that is beyond the scope of even this nerdy part of the explainer.

Another thing that digital can do is what we call the ACK/NAK handshake. When a data packet is sent across a network, the receiver verifies the packet mathematically to ensure it's error-free (among other things). If the packet is errorfree, the receiver sends an ACK (Acknowledge) back to the sender. The sender now sends the next packet and the process repeats itself.

If an error were introduced during transmission, the receiver would detect that and respond to the sender with a NAK (Negative Acknowledge) whereupon the sender would resend the same packet.

Most of the internet relies on this ACK/NAK handshake to ensure data reaches its destination safely and errorfree.

But over the air digital TV can't do that because it's a one-way flight only. Your TV cannot respond to a TV transmitter tower, after all. That's why OTA TV transmissions have Forward Error Correcting codes.