Calculate speed in a copper wire

In summary: The signal to noise ratio at the source is always 30dB... so you can use any rate you want without worrying about range. You just need to find the C value for that rate and then use the equation to find the range.
  • #1
dont_know
3
0
Okey, I have a problem now. I´m suposed to sketch a graf of how long range on a copper wire some different speeds have ex 256 kbit/s etc.

I have 225 channels of each 4kHz and it can transfer 4000 symbols/sec. The effect on each channel is 0.1mW and the noise is -100dBm.

The signal is reduced by 18 db/km

I´m using QAM-256 that means i can transfer 8 bits/symbol. It demands a SNR of 30db. Now i´m going to sketch a graf of the distance of some different speeds.


This far have I come (or am I totally lost?):

The bandwith is 900Mhz and SNR of the channel is 30db (30db = 10 log 1000 = S/N=1000) that gives: C=B log2 (1+S/N) C=900M*log2(1+1000)=7.2 Mbit/s

or a single channel:

C=4000*log2(1+1000)=398.7 kbit/s and then we have 225 channels that makes: 225*398.7=89,7 Mbit/s

Which one is the correct? If one is that say... That is speed att approximate 1 m and then I have to calculate the range of the speed with the 18 db/km?

But what about the symbols and bits? The effect of the channels and the noise?

Feeling quite lost now. Would be grateful for some help!

//Dont_know
 
Physics news on Phys.org
  • #2
C=900M*log2(1+1000)=7.2 Mbit/s

how are you getting 7.2Mbit/s here? I'm getting the same number you got using single channels and multiplying by 225.
 
  • #3
Oh. That is correct. When I checked what I wrote. I see some mistakes from my side. It shouldn´t be 900M but 900k.

I have looked at it on many different angles now. I´m staring to get somewhere now. But the limit in this channel is 8.97 Mbit/s. With the right equation:

C=900k*log2(1+1000)=8.97 Mbit/s
 
  • #4
Not sure if I'm fully understanding the question... it's been years since I did this stuff... But are you supposed to pick rates in bits/s and then plot the range for them... ie the distance when the signal to noise ratio becomes less than 30dB?

So what is the signal to noise ratio at the source... and how does it change with distance... is that what you need to work out?

just thinking out loud...
 

1. What is the formula for calculating speed in a copper wire?

The formula for calculating speed in a copper wire is speed = distance / time, where speed is measured in meters per second, distance is measured in meters, and time is measured in seconds.

2. How do you measure the distance in a copper wire?

The distance in a copper wire can be measured by using a ruler or tape measure to determine the length of the wire, or by using a tool such as a micrometer to measure the diameter of the wire and then calculating the length using the formula for circumference.

3. What units are typically used to measure speed in a copper wire?

The most common unit used to measure speed in a copper wire is meters per second (m/s), but other units such as miles per hour (mph) or kilometers per hour (km/h) can also be used.

4. How does temperature affect the speed of electricity in a copper wire?

Temperature can affect the speed of electricity in a copper wire by increasing or decreasing the resistance of the wire. Higher temperatures can cause the wire to expand, which in turn can increase resistance and slow down the speed of electricity. Lower temperatures can have the opposite effect, decreasing resistance and increasing the speed of electricity.

5. What factors can impact the accuracy of speed calculations in a copper wire?

The accuracy of speed calculations in a copper wire can be impacted by factors such as the temperature of the wire, the material and thickness of the wire, and external factors such as interference or variations in the power source. It is important to consider these factors and use precise measurements when calculating speed in a copper wire.

Similar threads

  • Engineering and Comp Sci Homework Help
Replies
6
Views
1K
  • Electrical Engineering
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
4K
  • Introductory Physics Homework Help
Replies
2
Views
2K
  • Introductory Physics Homework Help
Replies
2
Views
28K
  • Introductory Physics Homework Help
Replies
2
Views
5K
  • Earth Sciences
Replies
6
Views
8K
  • Introductory Physics Homework Help
Replies
5
Views
6K
  • Introductory Physics Homework Help
Replies
1
Views
1K
Replies
2
Views
2K
Back
Top