# Tag Info

57

The two reasons are simple: Eight frequencies are easier to discriminate with simple analog electronics - banks of bandpass filters or even vibrating reeds - than sixteen frequencies. The equally tempered scale is too close to the natural scale, which has simple fractional relationships between the frequencies. Consider that a phone line may be highly ...

51

It is exactly 4× the NTSC color-burst frequency of 3.579545 MHz. Since it is (well, used to be) used in huge quantities in commercial color TV sets, it is both commonly available, and particularly useful when you want to generate a signal to be displayed on such a TV.

49

From the Reuter's article referenced: SARAJEVO, March 7 (Reuters) - European power grid lobby ENTSO-E urged Serbia and Kosovo to urgently resolve a dispute over their power grid, which has affected the broader European network, causing some digital clocks on the continent to lose time. Figure 1. The ENTSO-E System Operations Committee has 5 permanent ...

36

I know that a square can be constructed from sine waves. However, the 555 does not generate sine waves or multiple frequencies, it generates a single square pulse. So where have these harmonic frequencies come from? Congratulations on your explanation of what you are seeing and your experimentation. The key issue is that not only CAN a square wave be ...

36

It's not a bad question and shows quite a common misunderstanding of how Radio Frequency (RF) Systems work. The 900MHz and 2600MHz signals are called Carrier Frequencies. The actual information is contained in the 10MHz bandwidth. The original signal is a baseband signal that extends up to 10MHz. This is used to modulate the carrier signal. The reason we do ...

34

AC and DC are relative terms. If you're looking at a 10kHz waveform for 100ns, you will think it is DC. It works the other way around too: if you forget about what's providing you with "DC", who knows if this waveform is not going to change in the next seconds, minutes, days, years? Think the voltage of a capacitor for example during slow discharge. If you ...

34

How a decrease in electricity production can lead to a decrease of the frequency on the grid on the long term? Isn't the frequency a parameter controlled by the power plant at the end of the day? Answered before: Why do generators have to rotate at a slower frequency if demand outpaces the supply? If the loss of power from some countries causes a ...

31

RF comms do not transmit one bit of information per cycle of the carrier wave - that would be digital baseband communications and it requires incredible amounts of bandwidth. Incidentally, you can buy FPGAs with built-in 28 Gbps serdes hard blocks. These can serialize and deserialize data for 100G ethernet (4x25G + coding overhead). I suppose the '...

30

Very clever, but that's not how it works. By your reasoning you should not only be able to make the frequency infinite, but also 4 Hz, or 100 Hz, or $\sqrt{2}$ Hz, all at the same time, with the same signal. And that's why you can't do that: a repeating signal can have only 1 fundamental frequency, which is 1/period. It would be the same as taking 2 ...

29

Nyquist-Shannon sampling theorem... often mis-used... If you have a signal that is perfectly band limited to a bandwidth of f0 then you can collect all the information there is in that signal by sampling it at discrete times, as long as your sample rate is greater than 2f0 it is very concise and contains within it two very key caveats PERFECTLY ...

29

A square wave can be viewed as a sum of the odd harmonics of a single frequency. A square wave can be generated by summing a bunch of sine waves. A square wave can also be generated by simply toggling the power on and off at the primary frequency of the square wave. In either case, the spectrum will look the same. You cannot tell how a square wave was ...

26

It uses something called a filter. You can build filters out of all sorts of different things. RC filters made out of resistors and capacitors are probably the simplest to understand. Basically, the capacitor acts as a resistor, but with a different resistance at different frequencies. When you add a resistor, you can build a voltage divider that is ...

24

Can I do this circuit practically o_O? Is there any transistor or IC that can oscillate 300 THz? Can I find an inductance (coil) of 0.0025 pH and capacitor of 1 pF? Not quite, no, and no. But this is an area of active research: The Truth About Terahertz. The basic principle of the tuned LC radio emitter is resonance. The techniques for producing high ...

24

This is like asking "how bright is a red light?". It's as bright as it is. You can make a bright red light or a dim red light. As another answer points out, the energy per photon of an electromagnetic signal depends on the frequency of the signal. But you can make a brighter or dimmer (higher or lower power) source at any frequency by emitting more or fewer ...

23

The underlying assumption in your question - that the frequency being measured is the rate at which electrons reverse polarity - is incorrect. The frequency of a signal at the transmitter, receiver, or anywhere in between physically corresponds to the cyclic arrival of a voltage. For example, in a digital application using amplitude modulation (let's assume ...

23

Forget sampling rate for a few seconds... Think about sampling period for a second, which is the time interval between two consecutive samples. This time can be an integer or any real number (as long as it’s positive, of course). Sampling rate is simply the inverse of sampling period. Does it make more sense this way?

22

FFTs work by treating signals as 2-dimensional -- with real and imaginary parts. Remember the unit circle? Positive frequencies are when the phasor spins counter-clockwise, and negative frequencies are when the phasor spins clockwise. If you throw away the imaginary part of the signal, the distinction between positive and negative frequencies will be lost. ...

21

There are turn-on and turn-off losses with every switching cycle, both in driving the switching elements themselves (gate drive loss if we're talking MOSFETs) and in the power train if you're considering a hard-switching topology like the step-down converters pictured in your question. Reducing the operating frequency reduces the number of these events per ...

21

The frequency you tune to is the centre frequency of the spectrum created by the modulation. The input from the aerial is generally modulated down to an intermediate frequency (to make it easier to work with) and then fed into a Phase-Locked Loop (PLL) circuit which creates a signal proportional to the frequency shift from the centre frequency. This signal ...

21

There are many reasons: - Cost: This is probably the biggest reason. The lighting market is quite competitive. There are lots of Chinese players offering aggressively cheap prices. This forces the other brands (even the bigger European ones like Osram, Philips, etc.) to use "cheaper" components to keep themselves in the game. As an employee for one of those ...

20

That "fixed frequency like 103.2Mhz" is a bit of a lie: the radio is tuned to receive a signal in a small frequency band, which width is matched to the modulation depth (variation in the transmitted frequency).

19

If you used single tones instead of dual tones, you'd need 16 of them instead of only 8 as in the DTMF system. Given that they have to be spaced far enough apart for reliable detection, and that you only have the range from 300 to 2700 Hz to work with, you'd probably find it difficult to decode that many different tones reliably using the technology ...

19

How can a decrease in electricity production lead to a decrease of the frequency on the grid on the long term? Isn't the frequency a parameter controlled by the power plant at the end of the day? You can think of the electricity grid as being like a giant mechanism. Induction motors are like belts that can slip a bit. Synchronous motors and generators are ...

19

The short answer: It doesn't. Arduino doesn't send anything close to that high. It can only send a lower frequency (lower bitrate) signal over a 433MHz CARRIER frequency (or any other frequency for that matter) by using another device/module which generates a very high frequency (radio frequency) in order to communicate via radio waves. The 433MHz in this ...

18

On 'one wire' there can only be one voltage present at any instance in time at a certain point on that wire. So if you add two sine waves the sum is no longer a sine wave but something else. The electrons move in the same complex fashion as well. Observe the animation source. The more frequencies you add the more complex the signal becomes. From a certain ...

18

Don't worry. Your PSU doesn't really work with AC. Most modern PSU fist change the AC to DC via a rectifier. The internal electronic then creates an own AC used to transform the voltage to the desired one. The internal AC has a much higher frequence to be more effecient. Most PSUs work with frequencies from 0 to over 60Hz. Even DC with down to 80V is ...

18

What I expected to see was a single peak at 2.5kHz. I don't know why. You need to reset your expectations. Think of this this way: If you just had a single peak, then the input would by definition be a sine wave. But you're feeding it a square wave, so how do you account for the difference? I know that a square can be constructed from sine waves. ...

18

Because the bandwidth of the channel determines how rapidly the symbols on that channel can change, not the carrier frequency. It is the bandwidth of the channel which determines how fast the channel "rings down" from a sudden change in phase or amplitude. So your two 10MHz bandwidth channels can each sustain a symbol rate of no more than $10 \cdot10^6$ ...

17

Yes, you can have AC with a frequency less than 1Hz, in the same way you can have numbers between 0 and 1. Frequency isn't an integer number, but a "real" number. You can quite happily have a waveform of $1 \times 10^{-100}Hz$ if you wanted. You'd have to be quite patient to see it change, but it will change, and given time it would trace an AC waveform....

17

There are two main reasons you are finding this challenging. First, you are using older and more discrete (lower scale integration) parts than would have been used to do this in the era of VGA. But next, you are using them in an atypical way. Specifically, your approach is not pipelined which means that you are having to add up multiple delays when ...

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