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Low calling capacity

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EngIntoHW

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Hi,

I was wondering what "low calling capacity" means.

I read that by dividing a channel's bandwidth into 3 channels, the calling capacity is increased, but so is the possibility of interference because the channel bandwidth is reduced.

What makes a signal that is transmitted in a certain frequency, to exceed beyond the channel's bandwidth and cause an interference with other channels?
 
Please try googling some of these simple things before asking.

About channel bandwidth interferring with adjacent channels, it has more to do with filters not having perfect brick wall roll offs so we can't make transmitters whose bandwidth is restricted soley to our desired frequency band nor can we make receivers that only pick out frequencies from that band. We could space channels really far apart (which is what they did in the early days of radio before there were better filters and receivers) but that'd be a lot of wasted RF bandwidth. This plays into the dividing a single channel's bandwidth into three different channels because you need sharper filters to achieve the same interference rejected from adjacent channels which is harder to do. This is for traditional AM and FM transmissions. Something similar occurs in spread spectrum though not quite exactly the same.

Calling capacity is exactly what it says it is. It's the capacity of a medium to handle a certain number of calls. "Low" is a relative term depending on the application.
 
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Please try googling some of these simple things before asking.
I understand, I'm really trying to read as much as possible.

About channel bandwidth interferring with adjacent channels, it has more to do with filters not having perfect brick wall roll offs so we can't make transmitters whose bandwidth is restricted soley to our desired frequency band nor can we make receivers that only pick out frequencies from that band. We could space channels really far apart (which is what they did in the early days of radio before there were better filters and receivers) but that'd be a lot of wasted RF bandwidth. This plays into the dividing a single channel's bandwidth into three different channels because you need sharper filters to achieve the same interference rejected from adjacent channels which is harder to do. This is for traditional AM and FM transmissions. Something similar occurs in spread spectrum though not quite exactly the same.
If a channel has 30KHz bandwidth and operates at 800MHz frequency (±15KHz), and then its divided into 3 10KHz channels, then you now actually have:
Channel #1: (800MHz - 10KHz) carrier frequency, 10KHz bandwidth.
Channel #2: (800MHz) carrier frequency, 10KHz bandwidth.
Channel #3: (800MHz + 10KHz) carrier frequency, 10KHz bandwidth.
?

Calling capacity is exactly what it says it is. It's the capacity of a medium to handle a certain number of calls. "Low" is a relative term depending on the application.

I see now, thank you.
So if you divide a certain bandwidth into 3 channels, you actually increase the calls capacity by 3?
and if you then divide each channel into 5 time slots, then you actually increased the call capacity by 15?
 
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If a channel has 30KHz bandwidth and operates at 800MHz frequency (±15KHz), and then its divided into 3 10KHz channels, then you now actually have:
Channel #1: (800MHz - 10KHz) carrier frequency, 10KHz bandwidth.
Channel #2: (800MHz) carrier frequency, 10KHz bandwidth.
Channel #3: (800MHz + 10KHz) carrier frequency, 10KHz bandwidth.
?
800MHz
800MHz + 5KHz
800MHz - 5kHz?

THe way you have it written requires a total of 40kHz bandwidth since each channel has 5kHz of bandwidth to either side of the center frequency. Ch1 and Ch3 center frequencies are smack dab on the very edges of your total available bandwidth.

It's very much like cramming a crapload of low quality videos onto a DVD, or just a few very high quality ones.
 
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800MHz
800MHz + 5KHz
800MHz - 5kHz?

THe way you have it written requires a total of 40kHz bandwidth since each channel has 5kHz of bandwidth to either side of the center frequency. Ch1 and Ch3 center frequencies are smack dab on the very edges of your total available bandwidth.

How come?
f(CH1) = 800MHz - 10KHz
Bandwidth(CH1) = [800MHz - 15KHz : 800MHz + 5KHz] = 10KHz

f(CH2) = 800MHz
Bandwidth(CH1) = [800MHz - 5KHz : 800MHz + 5KHz] = 10KHz

f(CH1) = 800MHz + 10KHz
Bandwidth(CH1) = [800MHz + 5KHz : 800MHz + 15KHz] = 10KHz

Bandwidth(Total) = [800MHz - 15KHz : 800MHz + 15KHz] = 30KHz
 
Wouldn't it be 30kHz? 20kHz between 790kHz and 810kHz, plus two 5kHz sidebands?
 

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