Communicating information a2 application topic

Hello, can someone please explain to me about the bandwidth , the one highlighter in pink?
I am quite confused about it.
Thanks a lot.


Posted from TSR Mobile

*the one highlighted in pink.


Posted from TSR Mobile

I'm not sure the info on that sheet is all correct tbh - usually the term 'sidebands' is used for the power at frequencies surrounding the carrier, not 'side frequencies'

The points I think it's trying to make is that

* the bandwidth depends on the highest audio frequency you want to transmit (also FM transmits stereo channels - more bandwidth is required for stereo too)
* the number of broadcast stations possible in a frequency range depends on the number of bandwidths you can fit in that range.

e.g.AM/ LW broadcast frequencies run from 153kHz to 279kHz - the range is 126kHz which allows you to have 14 channels each 9khz 'wide'
FM/VHF frequencies run from 88000kHz to 108000kHz - the range is 20000kHz which allows you 100 channels each 200kHz wide.

obviously LW and VHF have different propagation characteristics - LW stations are likely to interfere with each other over greater distances.

Hey, thanks a lot but I don't really get that part on the LW stations are likely to interfere with each other over greater distances. If each have a bandwidth of 9kHz wide which are different, how is this possible?


Posted from TSR Mobile

I don't like the article at all. Not very explanatory and quite confusing.

The longer the wavelength, then the less susceptible the signal is to atmospheric attenuation, obstruction by large obstacles (buildings, trees etc.) causing shadows behind them, signal reflection causing multiple signal paths and hence signal cancellation at the receiver etc.

Because of the longer range of LW transmission, signals intended for a limited local regional area can therefore unintentionally interfere with signals from another transmitter in a different region because both transmitters operate on the same frequency.

For instance (illustration only not real): 200KHz LW transmissions in Berkshire (music), interfering with signals from 200KHz LW transmissions in Hertfordshire (local news), interfering with signals from 200KHz transmissions in London (documentary). They all transmit at the same carrier frequency with reception intended only for their immediate local regions only, but because of the longer range of the LW signals, they can be picked up by receivers at the other locations also and hence the wanted signal is overlaid with the unwanted signal.

The problem gets worse for SW and LW at night because these frequencies can bounce of the ionosphere and be tranmsmitted many hundreds or even thousands of miles over-the-horizon to interfere with local signals.

Ionospheric bounce is exploited in over-the-horizon radar, which can detect objects/vessels over large parts of the earths surface.

Thank you very much in your help. I was just wondering about the example that you have stated. From what I know, each station has their own specific bandwidth of frequency . Although they are all LW , they are transmitted at different frequency. Thus they will not interfere with the others, no?



Posted from TSR Mobile

In the 21st century, the UK no longer uses LW, MW. Even the BBC is closing down FM transmissions to free up bandwidth.

on the contrary - my car radio receives nothing else .

probably I shouldn't have said obviously before, being rather old I played around with radios quite a lot when I was growing up before the web was invented. iirc everyone did and they'd have a feel for what stations you could get.

analogue radios are going to go the way of bicycle dynamos and all the other stuff that's useful for physics teacher explanations.

I always quite liked getting foreign stations tbh - felt a bit subversive. with DAB you only get to choose between the stations that the man has decided are appropriate for you.

lol. of course you are right, I should really have said 'started' the long road to analogues demise! boo hoo.

I hate DAB, iPods and most digital audio with a vengeance. I started out my love of electronics as a teenager through messing around with valve equipment and would avidly buy wireless world and practical electronics from Menzies every month. I am not old enough for Radio Caroline or the birth of Radio 1 even. But the BBC FM live concert broadcasts will be sorely and sadly missed when the switch over finally happens. My Quad ESL's will lose a part of themselves on that day. Thank goodness for vinyl.

Can't remember it either tbh though I do remember when medium wave stations were all known by wavelength rather than frequency.

which of course gives you a way of working out c if you can remember the before and after jingles