57
votes
If a square wave has infinite bandwidth, how can we see it on an oscilloscope?
We can't. We see a bandlimited version. That's obvious for two reasons:
perfect square signals cannot physically exist, for changing a voltage within 0 time would require an infinite amount of power
...
- 98.4k
41
votes
Accepted
Was the last mile copper wire not the limitation in dial-up internet service?
Is this...the same ...pair of copper wires that...was formerly used to provide dial-up internet service?
Same wires, but those wires weren't put there for dial-up, they were put there for voice. And, ...
- 3,339
37
votes
Accepted
How am I getting 1 Gbps through a CAT3 cable?
100 feet is not extremely long; so, as Dave says, you've got lucky, and your Gigabit Ethernet hardware is just exceedingly robust.
You have to realize that "Cat3" doesn't put an upper limit ...
- 98.4k
35
votes
Accepted
How is Wi-Fi throughput so high?
You're correct that the actual bandwidth for a single WiFi stream is rather narrow, ranging between 20 MHz for older specs and 160 MHz for 802.11ax. However, the spectral efficiency of WiFi is often ...
- 20.3k
26
votes
If a square wave has infinite bandwidth, how can we see it on an oscilloscope?
You are correct that an ideal square wave needs an infinite bandwidth as it contains frequencies up to infinite frequencies.
But this is theory, ideal square waves do not exist in the real world as ...
- 81.2k
20
votes
Why do FM radio signals occupy greater bandwidth than AM?
They need not, narrowband FM occupies the same bandwidth as AM, for the same audio bandwidth. Transmitted AM bandwidth is fixed at twice the audio bandwidth.
However, wide deviation FM provides ...
- 171k
18
votes
If a square wave has infinite bandwidth, how can we see it on an oscilloscope?
The 'scope won't show a perfect squarewave and if you zoom in on the timebase you should be able to see the rising and falling edges with some slope on them. This will be most obvious on an analogue ...
- 178k
15
votes
Why are USB devices slower than 480 MBit/s
This is a very old topic, but it has no answer yet. This is my attempt:
Why are today's implementations not capable of streaming at 53 MB/s?
The calculations are nearly fine, but you are ...
- 41.9k
14
votes
Accepted
How do I find an ADC circuit's bandwidth experimentally?
The bandwidth is the frequency for which the output is down 3 dB. It it a function of the analog portion of your circuit and does not depend on the sample rate nor the Nyquist rate which are basically ...
- 16.2k
14
votes
How am I getting 1 Gbps through a CAT3 cable?
The Ethernet speed negotiation process takes into account the capabilities of the devices at each end of the connection, but not the cable between them. Essentially, this means that if you connect two ...
- 249
14
votes
Accepted
Why do more transitions imply more bandwidth consumed?
That's because for an NRZ signal the fastest signal you can have on wire is an alternating ...101010... pattern which are the bits themselves. For a 1 Mbps data rate the maximum frequency of the ...
- 165k
13
votes
How is Wi-Fi throughput so high?
The Shannon-Hartley channel capacity equation tells us that:
$$C = B \log_2 (1 + S/N)$$
Where C is channel capacity, B is channel bandwidth, and S/N is signal to noise ratio.
The reason WiFi has made ...
- 56k
11
votes
Why do OOK transmissions have bandwidth?
Only an ideal sine wave with constant amplitude and single frequency that runs for infinitely long in time has extremely narrow bandwidth of a single peak. Having any changes to the ideal sine wave ...
- 165k
10
votes
Why do OOK transmissions have bandwidth?
On-Off Keying (OOK) is equivalent to AM modulation of the carrier with the data bit-stream with a 100 % modulation index.
As a result the entire spectrum of the bit stream is up-converted to the ...
- 3,042
10
votes
Is -3dB bandwidth defined for any type of transfer function?
Is -3dB bandwidth defined for any type of transfer function?
Maybe you do not realize what -3dB actually means?
-3 dB means that the amplitude of the voltage (current as well) has dropped by a factor ...
- 81.2k
10
votes
Accepted
Maximum Ethernet bandwidth through a slip ring
Maximum ethernet bandwidth is about maintaining the characteristic 100Ω (transmission line) impedance of the 10Gbe cable from device to device. As long as that can be done, you could use many ...
- 87.2k
10
votes
Accepted
Can analog bandwidth be modeled as an RC low-pass filter in this way?
Generally, 'bandwidth' without any further qualification means a -3dB bandwidth.
What happens beyond the -3dB point is unspecified. I would expect an oscilloscope, or any analogue data capture tool ...
- 171k
9
votes
Accepted
How do manufacturers limit bandwidth in oscilloscopes?
You should realize that sample rate (1 GS/s) and Bandwidth (70 MHz) are different things!!!
They are related in that a certain sample rate dictates the maximum bandwidth of the signals which can be ...
- 81.2k
9
votes
How am I getting 1 Gbps through a CAT3 cable?
Check the error counters on your attached equipment - managed switches generally keep a track of errors and collisions. It may be that this link is suffering errors, but at gigabit/s, it's still ...
- 883
9
votes
Accepted
Why are coaxial cables typically faster/longer than twisted pairs?
Why are coaxial cables typically faster/longer than twisted pairs?
The truth lies in the motivation for making twisted-pair (TP) cables: -
TP has closely magnetically coupled wires that naturally ...
- 467k
8
votes
Accepted
How to estimate the analog bandwidth?
If your scope's input amplifier has a frequency response of a first-order RC-filter, you can roughly estimate the bandwidth from the rise time:
$$BW ≈ 0.35 / t_R$$
To clarify, bandwidth is defined ...
- 26k
8
votes
Accepted
Op-amp speed: bandwidth vs slew rate
Here you have an answer via a graph which is present in the specification of the op-amp or you can calculate it. (example of LM324 https://www.onsemi.com/pdf/datasheet/lm324-d.pdf figure 7)
LM324 is a ...
- 15k
7
votes
Accepted
Gain-bandwidth product proof for open loop/closed loop opamp
Could you please tell me that if the wikipedia proof is wrong? I don't see any thing wrong with it.
The so called "proof" itself is wrong simply because they are using the Open Loop Gain to ...
- 989
7
votes
Accepted
What physical factor affects the antenna's bandwidth?
There are hundreds of different antennas so for my simple attempt at an answer I'll concentrate on the "dipole" and I'm not going to go into formulas too much.
What physical factor affects the ...
- 467k
7
votes
How do I find an ADC circuit's bandwidth experimentally?
The plots below (taken from here) show why calculating ADC 'bandwidth' from peak sample values may be problematic.
The plot on the right shows what happens when the sampling frequency is below the ...
- 56.8k
7
votes
Is bandwidth a parameter set in software by oscilloscope manufacturers?
Your colleague is basically right.
Some scopes are software upgradeable.
You can upgrade scope bandwidth or memory simply by purchasing a license.
Which means same hardware can be sold with different ...
- 165k
7
votes
How is Wi-Fi throughput so high?
For any given communication channel, the data carrying capacity is determined both by the channel width and by the signal to noise ratio. You could transmit 2Gbps over a 1kHz wide channel if you had a ...
7
votes
Can analog bandwidth be modeled as an RC low-pass filter in this way?
Assumptions aren't great here. For example, I have an old TDS460, which is rated 350MHz, but still has meaningful response up at 600, 800MHz even; it seems to drop off at roughly a 2nd-order ...
- 43.7k
7
votes
Slew rate and Bandwidth for 5 MHz signal
A couple of reasons.
First, the schematic shows no bypass caps on supply.
Second, you have built the circuit on a breadboard. You can't expect high performance analog or digital operation.
Third, it ...
- 165k
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