How do radio/tv signals travel?

[Average Joe]

Sorry didn't know where else to post this.

I'm reading this book right now, 'Multimedia Information Networking' that's basically all about data communications.

I've looked at some of this stuff before, and it always goes into really fine details about error detection and packet labelling and Pulse Code Modulation... all that ****.

What I'd really love is a general overview of how a signal gets from the radio/tv station to my house, in reasonably straightforward terms.

Like, what's the difference between an analog and digital signal in the air? Is it just a difference in the complexity of the waveform, digital being ^^^^ and analog being /~^^~~ ? Why is it even called digital when there clearly isn't 1s and 0s flying through the air!

Anyway, say it's a movie playing on terrestrial TV. So does the video signal go through a DAC at their station, then it gets amplified and beamed round in a circle at 100 Mhz or whatever, to be intercepted by your antenna and go through an ADC into your tv. I hope that's right, it's the difference between digital and analogue that get's me.

And this must be one meaty signal to be able to get over hills, round buildings and so on... what amplifies it?

Cheers, I'd just like a better overall picture before getting lost in all the finer details.

 

[peterhuang913]

Wow, this is complicated. But for signal strength, I think it can go over hills because the cycling of the data is very slow. That is that the wavelength is very long. As for the rest, I don't know.

 

[Average Joe]

Hehe, yeah it's something I'm sure many people take for granted. It seems like a simple concept but it's not really.

About the wavelength/cycle, I checked BBC1s signal frequency in the UK and it's 751.25Mhz - 757.25Mhz so the wavelength would be absolutely tiny.

Hmmn, well I'll try to find some more simple info. If I do I'll post it back, I really want a good mental image of how it works because I'm sure other stuff will fall into place more.

Cheers mate.

 

[peterhuang913]

I guess they either send the signal to satellites which blasts it back down or they send it to the sky which refracts and scatters the signal to the who region.

 

[superdave1984]

They send it through those little black cables.

 

[peterhuang913]

They send it through those little black cables.

I got that part, but him and I are confused on the airwave communications part.

 

[mikesgroovin]

They travel, trust me.

 

[NayNay1991x]

We have Some Big aerial where Everyone connects there Digital Freeview boxes and normal TV Channels its called Waltham transmitter in UK i drove near it and its very Tall must be over 400 feet high or more

 

[mssssee2]

Well Fm Signals are from about 85- 106 Mhz radiosignals, they can travel really far, about 50-100KM with no interruption. Tv signals are UHF from 175 to 850 Mhz, they also travel so far, but they need a big antenna to amplify the signal. They consist of the transmiters and the receivers, the transmiter sends the signals radially to the area and the receivers can get that signal, sometimes many transmiters are connected with underground cables to ensure better signal quality. Sorry I don't know anything else important cause we missed that chapter in Physics.

 

[Average Joe]

Well, sometimes it's easy to forget how amazing google is!

I've been making the mistake of treating radio waves the same as sound waves. Radio waves carry electricity, sound waves don't. I think I pretty much know how it works although there still might be some holes in the idea.

_____

The video signal goes through a Digital to Analogue Converter (DAC), and is converted from 1s and 0s to a varying voltage level.

This electrical signal is amplified and bandpass filtered so only the necessary frequencies are sent.

The signal is transmitted by an aerial at a frequency of 300-3000 MHz (Ultra High Frequency, or UHF). This is a relatively long wavelength in the electromagnetic spectrum, being 10cm to 1m long.

This signal bounces off charged particles and moisture in the atmosphere. If it's needed to travel longer distances, the signal can be amplified by a 'repeater' antenna. I imagine that a repeater will also bandpass filter the signal before retransmission.

Once the signal reaches your house, your antenna picks up the signal and feeds it down your wires. This signal then goes through an Analogue to Digital Converter (ADC) in your digital TV-box ready to be displayed on your TV.

_____

Note:

Radiowaves travel close to the speed of light: 300,000 Km/s.
'High Frequency' signals between 3 MHz and 30 MHz 'hug' the earth due to their longer wavelength.

The difference between digital and analogue is just the complexity of the waveform. One reason a digital signal is more reliable is because it's simpler, and therefore more distinguishable from noise interference.

You could use that crude example I gave earlier; Digital waveform - ^^^^^^^^^^, Analogue waveform - ^~~^\_/~^^~.


http://www.explainthatstuff.com/television.html
Radio waves - Wikipedia, the free encyclopedia
Techie Stuff - Analogue and digital terrestrial TV in Oxford