A2 Physics Communication help!!
Can anyone explain the highlighted text? And what exactly is meant by the LW, SW, MW and VHF and all, how are those related to AM and FM transmission?
(edited 4 years ago)
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Lw sw mw vhf are names given to radio frequency bands allocated for broadcast radio... You can look them up on Wikipedia but I don't think the examiners expect you to remember them and the definitions are slightly different in different parts of the world anyway.
The important ideas are that you can filter off high frequencies from music and speech at the transmitter and its still recognisable, just not very enjoyable or high quality to listen to... The benefit is that you can fit more radio stations in to the limited bandwidth of the low frequency lw and mw bands.
Otoh because the vhf broadcast band is about 20mhz wide there is space for lots of stations broadcasting music without needing to filter off the higher audio frequencies. So more choice and better quality sound.
The important ideas are that you can filter off high frequencies from music and speech at the transmitter and its still recognisable, just not very enjoyable or high quality to listen to... The benefit is that you can fit more radio stations in to the limited bandwidth of the low frequency lw and mw bands.
Otoh because the vhf broadcast band is about 20mhz wide there is space for lots of stations broadcasting music without needing to filter off the higher audio frequencies. So more choice and better quality sound.
Original post by Joinedup
Lw sw mw vhf are names given to radio frequency bands allocated for broadcast radio... You can look them up on Wikipedia but I don't think the examiners expect you to remember them and the definitions are slightly different in different parts of the world anyway.
The important ideas are that you can filter off high frequencies from music and speech at the transmitter and its still recognisable, just not very enjoyable or high quality to listen to... The benefit is that you can fit more radio stations in to the limited bandwidth of the low frequency lw and mw bands.
Otoh because the vhf broadcast band is about 20mhz wide there is space for lots of stations broadcasting music without needing to filter off the higher audio frequencies. So more choice and better quality sound.
The important ideas are that you can filter off high frequencies from music and speech at the transmitter and its still recognisable, just not very enjoyable or high quality to listen to... The benefit is that you can fit more radio stations in to the limited bandwidth of the low frequency lw and mw bands.
Otoh because the vhf broadcast band is about 20mhz wide there is space for lots of stations broadcasting music without needing to filter off the higher audio frequencies. So more choice and better quality sound.
Can you explain what is meant by bandwidth? And how/why exactly does FM have a greater bandwith than AM, how does that give FM some advantages and some disadvantages over AM?
I'm sorry, I know I'm asking for a lot. But I'm finding this topic quite difficult. And the text in my book and other resources isnt helping much. Thanks.
Bandwith is an amount of radio spectrum - it's quite simple to calculate for AM (2 times the maximum audio signal frequency you're going to transmit)
with the maximum signal frequency limited by low pass filters at the radio station to 4.5 kHz, the bandwidth required for each radio station is 9kHz
it's not simple to calculate the bandwidth of an FM signal but for audio limited to <15kHz it comes out at 200kHz - i.e. it's less efficient bandwidth use than AM but is judged to make up for that with immunity to interference from motorbike engines etc.
as the text says 9kHz is quite a large amount in comparison to the width of the low frequency bands.
LW broadcasting needs to fit in between 148.5 and 283.5kHz (there are international conventions about this) the difference between the highest and lowest LW broadcast frequency is 135kHz so there is space for 15 stations of 9kHz bandwidth before you have more than one station overlapping on to another and causing interference. That's a different number to the text you clipped in btw - there are other uses made of frequencies between 30kHz and 148.5Khz such as radio time signals
You would not be able to fit even one FM station with a 200kHz bandwidth in the allocated LW broadcast band.
FM broadcast stations are allocated much higher frequencies between 88MHz and 108MHz so there is enough space to fit 100 stations requiring 0.2MHz bandwidth each.
Additionally LW and MW radio signals can be detected at distances beyond a line of sight - so you can run a national LW station like Radio 4 with just one transmitter or a national MW station (like Radio 5) with 2 transmitters whereas to get national coverage with VHF FM stations requires many transmitters (eg classic radio) each covering a small area within its line of sight.
...
with the maximum signal frequency limited by low pass filters at the radio station to 4.5 kHz, the bandwidth required for each radio station is 9kHz
it's not simple to calculate the bandwidth of an FM signal but for audio limited to <15kHz it comes out at 200kHz - i.e. it's less efficient bandwidth use than AM but is judged to make up for that with immunity to interference from motorbike engines etc.
as the text says 9kHz is quite a large amount in comparison to the width of the low frequency bands.
LW broadcasting needs to fit in between 148.5 and 283.5kHz (there are international conventions about this) the difference between the highest and lowest LW broadcast frequency is 135kHz so there is space for 15 stations of 9kHz bandwidth before you have more than one station overlapping on to another and causing interference. That's a different number to the text you clipped in btw - there are other uses made of frequencies between 30kHz and 148.5Khz such as radio time signals
You would not be able to fit even one FM station with a 200kHz bandwidth in the allocated LW broadcast band.
FM broadcast stations are allocated much higher frequencies between 88MHz and 108MHz so there is enough space to fit 100 stations requiring 0.2MHz bandwidth each.
Additionally LW and MW radio signals can be detected at distances beyond a line of sight - so you can run a national LW station like Radio 4 with just one transmitter or a national MW station (like Radio 5) with 2 transmitters whereas to get national coverage with VHF FM stations requires many transmitters (eg classic radio) each covering a small area within its line of sight.
...
Original post by Joinedup
Bandwith is an amount of radio spectrum - it's quite simple to calculate for AM (2 times the maximum audio signal frequency you're going to transmit)
with the maximum signal frequency limited by low pass filters at the radio station to 4.5 kHz, the bandwidth required for each radio station is 9kHz
it's not simple to calculate the bandwidth of an FM signal but for audio limited to <15kHz it comes out at 200kHz - i.e. it's less efficient bandwidth use than AM but is judged to make up for that with immunity to interference from motorbike engines etc.
as the text says 9kHz is quite a large amount in comparison to the width of the low frequency bands.
LW broadcasting needs to fit in between 148.5 and 283.5kHz (there are international conventions about this) the difference between the highest and lowest LW broadcast frequency is 135kHz so there is space for 15 stations of 9kHz bandwidth before you have more than one station overlapping on to another and causing interference. That's a different number to the text you clipped in btw - there are other uses made of frequencies between 30kHz and 148.5Khz such as radio time signals
You would not be able to fit even one FM station with a 200kHz bandwidth in the allocated LW broadcast band.
FM broadcast stations are allocated much higher frequencies between 88MHz and 108MHz so there is enough space to fit 100 stations requiring 0.2MHz bandwidth each.
Additionally LW and MW radio signals can be detected at distances beyond a line of sight - so you can run a national LW station like Radio 4 with just one transmitter or a national MW station (like Radio 5) with 2 transmitters whereas to get national coverage with VHF FM stations requires many transmitters (eg classic radio) each covering a small area within its line of sight.
...
with the maximum signal frequency limited by low pass filters at the radio station to 4.5 kHz, the bandwidth required for each radio station is 9kHz
it's not simple to calculate the bandwidth of an FM signal but for audio limited to <15kHz it comes out at 200kHz - i.e. it's less efficient bandwidth use than AM but is judged to make up for that with immunity to interference from motorbike engines etc.
as the text says 9kHz is quite a large amount in comparison to the width of the low frequency bands.
LW broadcasting needs to fit in between 148.5 and 283.5kHz (there are international conventions about this) the difference between the highest and lowest LW broadcast frequency is 135kHz so there is space for 15 stations of 9kHz bandwidth before you have more than one station overlapping on to another and causing interference. That's a different number to the text you clipped in btw - there are other uses made of frequencies between 30kHz and 148.5Khz such as radio time signals
You would not be able to fit even one FM station with a 200kHz bandwidth in the allocated LW broadcast band.
FM broadcast stations are allocated much higher frequencies between 88MHz and 108MHz so there is enough space to fit 100 stations requiring 0.2MHz bandwidth each.
Additionally LW and MW radio signals can be detected at distances beyond a line of sight - so you can run a national LW station like Radio 4 with just one transmitter or a national MW station (like Radio 5) with 2 transmitters whereas to get national coverage with VHF FM stations requires many transmitters (eg classic radio) each covering a small area within its line of sight.
...
What exactly does the sentence "on the long wave (LW) and medium wave (MW) wavebands, the bandwidth on an AM radio station is 9 kHz".
Similarly, what does "On the very high frequency (VHF) waveband, the bandwidth of an FM radio station is about 200 kHz" mean?
Whats the point of mentioning wavebands really? I'm sorry, but my understanding of the topic Telecom is really poor.
Original post by UnknownCookie
What exactly does the sentence "on the long wave (LW) and medium wave (MW) wavebands, the bandwidth on an AM radio station is 9 kHz".
Similarly, what does "On the very high frequency (VHF) waveband, the bandwidth of an FM radio station is about 200 kHz" mean?
Whats the point of mentioning wavebands really? I'm sorry, but my understanding of the topic Telecom is really poor.
Similarly, what does "On the very high frequency (VHF) waveband, the bandwidth of an FM radio station is about 200 kHz" mean?
Whats the point of mentioning wavebands really? I'm sorry, but my understanding of the topic Telecom is really poor.
each AM station needs a 9kHz 'slice' and each FM station needs a 200kHz 'slice'
at typical VHF frequencies around 100MHz a slice 200kHz wide isn't a big deal and there are plenty of slices available. 100MHz is much bigger than 200kHz
at typical longwave frequencies around 200kHz a slice that is 200kHz wide is going to be a huge problem because the size of the slice required is similar to the carrier frequency... one FM station centred at 200kHz would take a slice starting at 100kHz and ending at 300kHz
but all the longwave stations have to fit between 185.5 and 283.5kHz
This is a general rule btw - if you want a lot of transmitters to all be able to work at the same time without jamming each other it's preferable to use high radio frequency so there's more space available for each transmitter to have a slice - look up the frequencies used by modern systems like wi-fi or mobile phones.
Original post by Joinedup
each AM station needs a 9kHz 'slice' and each FM station needs a 200kHz 'slice'
at typical VHF frequencies around 100MHz a slice 200kHz wide isn't a big deal and there are plenty of slices available. 100MHz is much bigger than 200kHz
at typical longwave frequencies around 200kHz a slice that is 200kHz wide is going to be a huge problem because the size of the slice required is similar to the carrier frequency... one FM station centred at 200kHz would take a slice starting at 100kHz and ending at 300kHz
but all the longwave stations have to fit between 185.5 and 283.5kHz
This is a general rule btw - if you want a lot of transmitters to all be able to work at the same time without jamming each other it's preferable to use high radio frequency so there's more space available for each transmitter to have a slice - look up the frequencies used by modern systems like wi-fi or mobile phones.
at typical VHF frequencies around 100MHz a slice 200kHz wide isn't a big deal and there are plenty of slices available. 100MHz is much bigger than 200kHz
at typical longwave frequencies around 200kHz a slice that is 200kHz wide is going to be a huge problem because the size of the slice required is similar to the carrier frequency... one FM station centred at 200kHz would take a slice starting at 100kHz and ending at 300kHz
but all the longwave stations have to fit between 185.5 and 283.5kHz
This is a general rule btw - if you want a lot of transmitters to all be able to work at the same time without jamming each other it's preferable to use high radio frequency so there's more space available for each transmitter to have a slice - look up the frequencies used by modern systems like wi-fi or mobile phones.
I hope you could answer another question of mine. This might sound stupid, but I'm really confused on it.
Suppose, you have a bandwidth of 9 kHz (AM transmission). A bandwidth of 9 kHz I believe means that the difference between the highest frequency and lowest frequencies contained in the signal is 9 kHz. Suppose, the frequencies of the audio signal are in the range 18-27 kHz (minimum frequency of the audio signal being 18 and maximum being 27 kHz). According to this, the maximum frequency being transmitted is 27 kHz and not 4.5 kHz as I was told it is for AM transmissions having a 9 kHz bandwidth!
I know I'm wrong. I just want to be corrected so I learn what I don't understand. Thank you very much.
Original post by UnknownCookie
I hope you could answer another question of mine. This might sound stupid, but I'm really confused on it.
Suppose, you have a bandwidth of 9 kHz (AM transmission). A bandwidth of 9 kHz I believe means that the difference between the highest frequency and lowest frequencies contained in the signal is 9 kHz. Suppose, the frequencies of the audio signal are in the range 18-27 kHz (minimum frequency of the audio signal being 18 and maximum being 27 kHz). According to this, the maximum frequency being transmitted is 27 kHz and not 4.5 kHz as I was told it is for AM transmissions having a 9 kHz bandwidth!
I know I'm wrong. I just want to be corrected so I learn what I don't understand. Thank you very much.
Suppose, you have a bandwidth of 9 kHz (AM transmission). A bandwidth of 9 kHz I believe means that the difference between the highest frequency and lowest frequencies contained in the signal is 9 kHz. Suppose, the frequencies of the audio signal are in the range 18-27 kHz (minimum frequency of the audio signal being 18 and maximum being 27 kHz). According to this, the maximum frequency being transmitted is 27 kHz and not 4.5 kHz as I was told it is for AM transmissions having a 9 kHz bandwidth!
I know I'm wrong. I just want to be corrected so I learn what I don't understand. Thank you very much.
Because the radio bandwidth available at the frequencies used for AM is limited, the high audio frequencies are electronically removed before modulation (technically this is called filtering) and that makes the bandwidth slice for each station smaller so more radio stations are able to exist.
limiting the maximum audio frequencies to 4.5kHz allows recognisable speech and music - but it doesn't sound like 'high quality' audio
using AM 9kHz radio bandwidth can only broadcast audio frequencies up to 4.5kHz - you get 4.5 kHz going into the frequencies above the carrier frequency and 4.5 below. AM is not very efficient but it it is cheap and simple - which was the most important thing in the 1920s when it was being introduced.
FM radio was developed after WW2 when it was possible to make more complicated circuits cheaply and it has a higher audio cut off frequency.
Original post by Joinedup
using AM 9kHz radio bandwidth can only broadcast audio frequencies up to 4.5kHz - you get 4.5 kHz going into the frequencies above the carrier frequency and 4.5 below. AM is not very efficient but it it is cheap and simple - which was the most important thing in the 1920s when it was being introduced.
Meaning, suppose we have a carrier frequency 200 kHz and in AM transmission (where bandwidth is 9 kHz), our transmitted audio signal in that case for a particular radio station will only have frequencies from 195.5 kHz to 204.5 kHz? And not out of that range (because the audio signal frequencies out of that range are filtered out to fit in more AM radio stations)?
Thank you very much again. You've been of great help.
(edited 4 years ago)
Original post by Joinedup
Because the radio bandwidth available at the frequencies used for AM is limited, the high audio frequencies are electronically removed before modulation (technically this is called filtering) and that makes the bandwidth slice for each station smaller so more radio stations are able to exist.
limiting the maximum audio frequencies to 4.5kHz allows recognisable speech and music - but it doesn't sound like 'high quality' audio
using AM 9kHz radio bandwidth can only broadcast audio frequencies up to 4.5kHz - you get 4.5 kHz going into the frequencies above the carrier frequency and 4.5 below. AM is not very efficient but it it is cheap and simple - which was the most important thing in the 1920s when it was being introduced.
FM radio was developed after WW2 when it was possible to make more complicated circuits cheaply and it has a higher audio cut off frequency.
limiting the maximum audio frequencies to 4.5kHz allows recognisable speech and music - but it doesn't sound like 'high quality' audio
using AM 9kHz radio bandwidth can only broadcast audio frequencies up to 4.5kHz - you get 4.5 kHz going into the frequencies above the carrier frequency and 4.5 below. AM is not very efficient but it it is cheap and simple - which was the most important thing in the 1920s when it was being introduced.
FM radio was developed after WW2 when it was possible to make more complicated circuits cheaply and it has a higher audio cut off frequency.
I have one more question. For e.g the range in the LW waveband is 270 kHz, we can fit in 30 radio stations using AM transmission (keeping the usual 9 kHz AM bandwidth between each radio station). What does carrier frequency mean in this context? How can we think of carrier frequency in this e.g? trying to understand about carrier frequency better. Thanks.
Original post by UnknownCookie
I have one more question. For e.g the range in the LW waveband is 270 kHz, we can fit in 30 radio stations using AM transmission (keeping the usual 9 kHz AM bandwidth between each radio station). What does carrier frequency mean in this context? How can we think of carrier frequency in this e.g? trying to understand about carrier frequency better. Thanks.
not quite sure what you're asking - if there were 30 stations all broadcasting silence you'd have narrow spikes of RF energy every 9kHz with nothing in between (except the background RF from natural sources)
Here's a video that might help you think about it https://www.youtube.com/watch?v=1wUjLWNgqMs
the guy has quite a bit to say and it's not important that you understand all of it... but importantly he's showing the same amplitude modulated signals on two instruments...
1. oscilloscope (black and green screen) which shows amplitude on the vertical axis and time on the horizontal axis
2. spectrum analyser (black and white screen) which shows amplitude on the vertical axis and frequency on the horizontal axis
he's using a 10kHz audio frequency for illustration purposes which means his signal has a higher bandwidth than is used in AM broadcasting - he's just doing a demo of the principles for the camera.
Original post by Joinedup
not quite sure what you're asking - if there were 30 stations all broadcasting silence you'd have narrow spikes of RF energy every 9kHz with nothing in between (except the background RF from natural sources)
Here's a video that might help you think about it https://www.youtube.com/watch?v=1wUjLWNgqMs
the guy has quite a bit to say and it's not important that you understand all of it... but importantly he's showing the same amplitude modulated signals on two instruments...
1. oscilloscope (black and green screen) which shows amplitude on the vertical axis and time on the horizontal axis
2. spectrum analyser (black and white screen) which shows amplitude on the vertical axis and frequency on the horizontal axis
he's using a 10kHz audio frequency for illustration purposes which means his signal has a higher bandwidth than is used in AM broadcasting - he's just doing a demo of the principles for the camera.
Here's a video that might help you think about it https://www.youtube.com/watch?v=1wUjLWNgqMs
the guy has quite a bit to say and it's not important that you understand all of it... but importantly he's showing the same amplitude modulated signals on two instruments...
1. oscilloscope (black and green screen) which shows amplitude on the vertical axis and time on the horizontal axis
2. spectrum analyser (black and white screen) which shows amplitude on the vertical axis and frequency on the horizontal axis
he's using a 10kHz audio frequency for illustration purposes which means his signal has a higher bandwidth than is used in AM broadcasting - he's just doing a demo of the principles for the camera.
I'm sorry, I realise what I was saying didn't make any sense. Anyway, I understand now. Thank you.
Original post by Joinedup
not quite sure what you're asking - if there were 30 stations all broadcasting silence you'd have narrow spikes of RF energy every 9kHz with nothing in between (except the background RF from natural sources)
Here's a video that might help you think about it https://www.youtube.com/watch?v=1wUjLWNgqMs
the guy has quite a bit to say and it's not important that you understand all of it... but importantly he's showing the same amplitude modulated signals on two instruments...
1. oscilloscope (black and green screen) which shows amplitude on the vertical axis and time on the horizontal axis
2. spectrum analyser (black and white screen) which shows amplitude on the vertical axis and frequency on the horizontal axis
he's using a 10kHz audio frequency for illustration purposes which means his signal has a higher bandwidth than is used in AM broadcasting - he's just doing a demo of the principles for the camera.
Here's a video that might help you think about it https://www.youtube.com/watch?v=1wUjLWNgqMs
the guy has quite a bit to say and it's not important that you understand all of it... but importantly he's showing the same amplitude modulated signals on two instruments...
1. oscilloscope (black and green screen) which shows amplitude on the vertical axis and time on the horizontal axis
2. spectrum analyser (black and white screen) which shows amplitude on the vertical axis and frequency on the horizontal axis
he's using a 10kHz audio frequency for illustration purposes which means his signal has a higher bandwidth than is used in AM broadcasting - he's just doing a demo of the principles for the camera.
I've moved on the last topic of the chapter, "communication channels" and have a few questions from satellite communication I'd be very thankful if you helped answer.
I don't really understand what they mean by the text highlighted in red that says " The two carrier wave frequencies are different to prevent the satellites high power transmitted signal swamping it's reception of the low power signal that it receives. There is no interference of the actual information being carried by the waves because this is stored as a modulation of the carrier waves".
In the second highlighted text, please explain the highlighted reasons why satellite communication isn't used without a satellite in the SW and MW wavebands, knowing it can possibly be used.
Thank you very much.
(edited 4 years ago)
The problem of swamping if a satellite attempted to receive and transmit on the same frequencies is hopefully easy to understand. Transmission and reception are both Continuous.
Tbh I don't understand what it says about stored as modulation... The frequencies are selected so that the harmonics of the lower frequency won't interfere with the higher frequency (I. E the higher frequency is not a whole number multiple of the lower frequency)
The second paragraph is comparing long distance communication using satellites to long distance communication without satellites.
There's pros and cons both ways tbh... If you listen to time signal beeps on a satellite telly and an analogue radio at the same time the satellite is behind the analogue radio by a very noticeable amount. This is due to the large distance covered by the sattelite radio waves making a long 2 way trip . That's not really important for some applications like entertainment/telly watching, but is for other applications.
Satellites can do high bandwidth with expensive dish ariels and complicated recievers... but perhaps low bandwidth with cheap, simple (and low energy consumption) recievers is suitable for some applications. .. Such as the radio teleswitch service in the UK or the time service stations like MSF or DCF77
Tbh I don't understand what it says about stored as modulation... The frequencies are selected so that the harmonics of the lower frequency won't interfere with the higher frequency (I. E the higher frequency is not a whole number multiple of the lower frequency)
The second paragraph is comparing long distance communication using satellites to long distance communication without satellites.
There's pros and cons both ways tbh... If you listen to time signal beeps on a satellite telly and an analogue radio at the same time the satellite is behind the analogue radio by a very noticeable amount. This is due to the large distance covered by the sattelite radio waves making a long 2 way trip . That's not really important for some applications like entertainment/telly watching, but is for other applications.
Satellites can do high bandwidth with expensive dish ariels and complicated recievers... but perhaps low bandwidth with cheap, simple (and low energy consumption) recievers is suitable for some applications. .. Such as the radio teleswitch service in the UK or the time service stations like MSF or DCF77
Original post by Joinedup
The problem of swamping if a satellite attempted to receive and transmit on the same frequencies is hopefully easy to understand. Transmission and reception are both Continuous.
What do you mean when you say "transmission and reception are both continuous?"
Original post by Joinedup
The frequencies are selected so that the harmonics of the lower frequency won't interfere with the higher frequency (I. E the higher frequency is not a whole number multiple of the lower frequency)
What exactly happens if there is interference between both the frequencies?
Original post by Joinedup
The second paragraph is comparing long distance communication using satellites to long distance communication without satellites.
Hope you could answer a few more questions from this para. The text says "long distance communication WITHOUT satellites is possible only in the SW and MW wavebands". Why is that? Why isn't long distance communication possible without satellites in the SHF and EHF wavebands?
I wish to ask, are the 3 reasons stated the reasons for why "satellite communication (space wave transmission)" has replaced the use of "sky wave transmission by ionospheric reflection"?
(edited 4 years ago)
Those are all my remaining queries from the chapter "Communications".
Original post by UnknownCookie
What do you mean when you say "transmission and reception are both continuous?"
What exactly happens if there is interference between both the frequencies?
Hope you could answer a few more questions from this para. The text says "long distance communication WITHOUT satellites is possible only in the SW and MW wavebands". Why is that? Why isn't long distance communication possible without satellites in the SHF and EHF wavebands?
I wish to ask, are the 3 reasons stated the reasons for why "satellite communication (space wave transmission)" has replaced the use of "sky wave transmission by ionospheric reflection"?
What exactly happens if there is interference between both the frequencies?
Hope you could answer a few more questions from this para. The text says "long distance communication WITHOUT satellites is possible only in the SW and MW wavebands". Why is that? Why isn't long distance communication possible without satellites in the SHF and EHF wavebands?
I wish to ask, are the 3 reasons stated the reasons for why "satellite communication (space wave transmission)" has replaced the use of "sky wave transmission by ionospheric reflection"?
The radio signal going from the earth to the satellite is very weak when it reaches the satellite due to distance, there is an inverse square law governing intensity... but any emission from the satellite is very close to the receiving antenna on the satellite (satellites are relatively small). The wanted signal from the ground station would be incredibly weak in comparison to emissions coming from the satellite on the same frequency.
---
The ionosphere is reflective at some frequencies and transparent at other frequencies - the frequencies that work for over the horizon terrestrial radio are the frequencies where it's reflective and the frequencies that work for satellite communications are the frequencies where it is transparent.
Original post by UnknownCookie
What do you mean when you say "transmission and reception are both continuous?"
Oh right - you can do 2 way (or more than 2) communication on the same frequency if everyone takes it in turns and only talks one at a time - this is how old school CB radios and walkie talkies work. it's a bit different to using a phone*. when a user wants to talk the radio switches off it's receiver and switches on its transmitter and when they've finished talking the radio switches off its transmitter and switches it's receiver on.
You do need to organise ways to ensure everyone know when they're allowed to talk and to recover from situations where 2 or more people talk at the same time (jamming eachother)
It's got applications where people only want to talk for a small fraction of the time but isn't going to be useful for satellite TV.
-----
*Phone is full duplex - so for example someone can be telling you something sad and you can make oooh ahh sympathetic noises while they're talking and they will be able to hear you - so it's more like having a normal face to face conversation
walkie talkie is half duplex - meaning strict turn taking is required.
Original post by Joinedup
Oh right - you can do 2 way (or more than 2) communication on the same frequency if everyone takes it in turns and only talks one at a time - this is how old school CB radios and walkie talkies work. it's a bit different to using a phone*. when a user wants to talk the radio switches off it's receiver and switches on its transmitter and when they've finished talking the radio switches off its transmitter and switches it's receiver on.
You do need to organise ways to ensure everyone know when they're allowed to talk and to recover from situations where 2 or more people talk at the same time (jamming eachother)
It's got applications where people only want to talk for a small fraction of the time but isn't going to be useful for satellite TV.
-----
*Phone is full duplex - so for example someone can be telling you something sad and you can make oooh ahh sympathetic noises while they're talking and they will be able to hear you - so it's more like having a normal face to face conversation
walkie talkie is half duplex - meaning strict turn taking is required.
You do need to organise ways to ensure everyone know when they're allowed to talk and to recover from situations where 2 or more people talk at the same time (jamming eachother)
It's got applications where people only want to talk for a small fraction of the time but isn't going to be useful for satellite TV.
-----
*Phone is full duplex - so for example someone can be telling you something sad and you can make oooh ahh sympathetic noises while they're talking and they will be able to hear you - so it's more like having a normal face to face conversation
walkie talkie is half duplex - meaning strict turn taking is required.
Need help with this. I know increased bandwidth means more information can be transmitted, but how does that help in reducing the cost of telephone calls?
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