# Questions tagged [frequency]

How many times something happens per second, measured in Hz (hertz).

131 questions
Filter by
Sorted by
Tagged with
10k views

### Why do utility companies supply at a frequency of either 50/60 Hz?

It just struck me that Utility Companies world-wide supply domestic users at either 50/60Hz. It could have been selected to be 10 Hz, or 100 Hz ... whatever Was 50/60 chosen at random? Is there some ...
• 3,011
20k views

### How precise is the frequency of the AC electricity network?

If I make a digital clock which first detects the AC frequency roughly (whether it is 50, 60, 100Hz, etc), then uses it as its clock pulse source, how precise would it be? Would it work world wide ...
• 14k
25k views

### How to convert AC to DC

I am designing a circuit that needs to output 5VDC @ 1A. I'm trying to use a wall transformer to step the voltage down to 12VAC. The next step is the diode bridge and ripple capacitor. The ripple ...
• 3,232
19k views

### How critical are UART frequencies?

I'm going to be using an 8 MHz crystal to run my microcontroller at 16 MIPS (PLL 4x, 2 cycle instructions.) However, 8 MHz doesn't divide into any UART frequencies AFAIK... so how critical are these ...
• 31.7k
5k views

### Why is an op amp's bandwidth higher at lower gains?

If I build a resistor network where the op amp has a lower gain, it is able to maintain its gain for a larger bandwidth. Why?
• 653
5k views

### Basic Frequency Control Circuit

How does R4 prevent the output voltage drifting towards one of the supply rails to the op amp? I understand that R4 has to have a high resistance but I do not know why? Here is the schematic which is ...
• 365
3k views

### 15V 3A dc motor PWM frequency setting

What is a suitable frequency for 15V/3A DC motor? Is there any effect on the motor when the frequency is changing? I am confused with this until now and the Internet shows a lot of theory that ...
17k views

### What is the equation for the 555 timer control voltage?

I was just wondering what the equation is to find the 555's output frequency is, when a control voltage is applied to pin 5. That would be very useful for me to know! [Edit By OP] So based on what ...
• 199
6k views

### Negative frequencies: what is that?

I know that when the frequency is 0, the voltage will be pure DC. But in DSP and Digital Communication, I have seen mentioning of negative frequencies which I dont quite understand. For example, like \...
• 2,245
50k views

### Changing the frequency of an AC supply

I am using an AC Power supply, and the frequency of the wall plugs is around 50hz. Is there a way to increase this frequency keeping everything the same?
• 2,326
51k views

### Resonant Frequency from Bode plot

If we have a transfer function that shows no peaking in the magnitude bode plot (Starting from a flatline and then rolling off). Does this mean that there is no resonant frequency? Or do we consider ...
808 views

Is it possible to read a set of frequencies with a PIC in such a way that for each frequency a different function is called? The idea was to send multiple frequencies at different times (no ...
• 249
1 vote
10k views

### Frequency Detection Circuit Design

I want to create a circuit that can detect audio frequencies and flash RGB LEDs different colors depending on the detected frequency. The frequency range will be from 20 Hz to 12 kHz, after looking at ...
• 1,254
13k views

### Serbia, Kosovo power grid row delays European clocks. Why?

According to this article (and a lot more published today on the same topic), Kosovo electricity net production balance has decreased during the last weeks. This has led to a small deviation of the ...
• 733
17k views

### Why does a faster clock require more power?

If you overclock a microcontroller, it gets hot. If you overclock a microcontroller, it needs more voltage. In some abstract way it makes sense: it is doing more computation, so it needs more energy ...
• 2,025
3k views

### How do you visualize negative Frequency in Time domain ?

In the field of Digital signal processing I have seen people using words Complex signals and Negative frequencies. For eg. in FFT Spectrum. Does it really have significant meaning in the time domain ...
• 570
6k views

### Characterization of bypass capacitors

I was reading through a few post including Decoupling caps as well as this app note Xilinx Power Distribution Network. I have a question regarding capacitor values within a power distribution system. ...
• 546
4k views

### How can over 24 GHz communication be possible?

I read the article Google wants the US' wireless spectrum for balloon-based Internet. It says to use over 24 GHz frequency spectrum for communication. Is it ever possible to generate that high ...
• 477
4k views

### Frequency ranges that causes a hazard to humans

I hope many people might feel little awkward to see this question. But I feel this is important. Because in my place where I am living I can get a radio (Audio Receiver) very cheaply. I don't know ...
• 469
15k views

### Maximum sample rate of Arduino Duemilanove?

G'day all! I have an Arduino Duemilanove hanging around spare at the moment and thought I might try a few audio interfacing projects. I'm just wondering what sort of sampling frequency I can achieve ...
617 views

### mains frequency accuracy worldwide

I like to build a device that needs long term time stability. In germany, one of the best simple clocks use the mains power frequency to obtain a time measure. While the frequency is allowed to change ...
• 553
1k views

### Why can an oscilloscope only find frequencies 1/10 of the sampling frequency, despite Nyquist?

The oscilloscope at my university states both its sampling frequency and the maximum frequency that it can detect. However, the maximum frequency is just 1/10 of the sampling frequency! Nyquist's ...
• 143
4k views

### What does 100Ohm @ 100MHz exactly mean in ferrite beads?

I am trying to understand the parameters of ferrite beads and having trouble in understanding the impedance vs frequency parameter. What does 100Ohm at 100MHz exactly mean? Does it mean that the ...
• 425
14k views

### Why is Cat5/Cat5e Ethernet cable rated 100MHz?

As the questions says, is there any specific reason why Ethernet cable is rated 100MHz? For a 100Mbps Ethernet the data rate is 100Mbps, and the baud rate is 125Mbaud, because of the specific line ...
• 425
2k views

### Obtaining Poles and Zeros from frequency response

What is the process of obtaining the poles and zeros from frequency response plot or data. Any reference or Matlab code will be great help
5k views

### Does a bridge rectifier care that much for AC frequency?

As I understand it, a bridge rectifier is a set of diodes that play a trick of logic that keeps the polarity positive. So, within the context of a household DC transformer does it matter what the ...
• 387
2k views

### Electrical Motors and Frequency

I was musing about electric motors after seeing one randomly on TV, and there's something I'm must be remembering incorrectly. It's just a thought experiment, so I'm imagining some theoretical DC ...
• 357
1k views

### looking for a sensor that activates when hit by a certain frequency burst

I have a question that may seem silly, but I am only new at this type of thing:  Is there a sensor that I could connect to an LED (via an integrated circuit of some description, I assume) that ...
137 views

### Is it possible to connect an antenna of the proper length to a CPU and radiate its 4 GHz oscillating current?

Since a 4 GHz CPU has been made to provide that super high frequency, is it possible to connect an antenna of the right length to it and radiate its 4 GHz oscillating current?
• 21
259 views

### Finding frequency of a series of pulses (3 - 60 Hz) without using a microcontroller or frequency-to-voltage converter

I came across an interesting yet challenging problem of finding the frequency of a series of pulses. The pulses can have a frequency anywhere from 1 to more than 100 Hz. The goal is to detect if the ...
• 103
242 views

### Electromagnetic charging

I'm building a circuit that uses a really low voltage and current. I thought that instead of using a standard battery it would be nice if I could use a rechargeable battery and charge it with ...
• 155
451 views

### Parasitic effects on passive elements at high frequency

What would the magnitude response curve for a resistor, inductor and capacitor look like with parasitic effects not ideal components? From what I have gathered they would look something along the ...
• 451
423 views

### Finding the cut-off frequency

Find the cut-off frequency of this filter: My attempt: \text{H}\space_{\left(\omega\right)}=\frac{\text{R}_1+j\omega\text{L}}{\text{R}_1+\text{R}_2+j\omega\text{L}}=\frac{\text{R}_1+j\omega\text{L}...
• 7,436
59 views

### Can't understand concept, range of the pulse (waveform)

I am working on the lab which is allowed to ask other people for hints. In the image, program called "Audacity" is used to capture that waveform. Question 1 In the image it says, "The peak-to-...
• 1
786 views

### Can a smartphone send directly a message to another smartphone 20 miles away? [duplicate]

According to this website, a typical cellphone has enough power to reach a cell tower up to 45 miles away So, can a smartphone send directly a message to another smartphone 20 miles away?
• 11
2k views

### What are 12.000393 MHz crystals used for?

I found them on www.digikey.com, and they're apparently made by different manufacturers, so there must be some use for them. What are they used for? edit and why? The 2400 baud modem doesn't offer an ...
• 9,678
6k views

### Where do overtones in a 555 generated square wave come from?

I have built a 555 oscillator and connected it to a speaker. Using an oscilloscope I adjusted the 555 to generate a 2.5kHz square wave. I then held a microphone up to the speaker and fed the input ...
• 593
5k views

### Are antennas specified for a certain frequency?

"LTE 868 MHz Antenna" Why does 868 MHz stand for? Are antennas specified for a certain frequency or is it necessary for something like input type? For example, I want to transmit a 40 MHz RF ...
• 399
52k views

### Is frequency for dc zero Hz?

We know the frequency of a direct current is zero. The reason is that there is no repetitive pattern. But I was stumbled when I noticed, why can't that straight line be cut into smaller pieces, and ...
• 2,493
2k views

### Why do most flyback converters / LED drivers operate under 100 kHz?

Most of the LED drivers and flyback converters I have come across operate in the 60-100 kHz range. Is there any particular reason behind this - example - ferrite cores not being able to handle higher ...
• 8,276
35k views

### How exactly are radio waves produced from a current in a circuit itself?

I am 17, and I am new to electronics, and I've learned everything online and expect to continue to do so with all the resources. I have dug around and can't find concise answers on this question ... ...
• 111
12k views

### How does an AM radio filter out only the desired frequency?

I understand that electromagnetic waves in the air induce an alternating current in the antenna. I also understand how, once you filter the signal to obtain the desired frequency, you can get the ...
• 238
42k views

### What is Frequency in electronics?

This has been floating in my mind for a while, everything has a frequency. Like a dc-dc converter, my scope is 100 MHz(i know that's a bandwidth but it has the unit of frequency). I understand that an ...
• 8,418
5k views

### MC34063A: Why am I overclocking this chip?

I've decided to get some experience with DC-DC converters and I've obtained an Onsemi MC34063A DC-DC converter. From documentation I've got the datasheet, the AN920 application note and the Excel ...
• 23.3k
2k views

### What frequency stability crystal do we need?

We're designing a simple digital clock and using a 32.768 kHz crystal with a frequency stability of 20 ppm (standard off-the-shelf SMT). We're finding the clock is running fast by about 2.5 minutes ...
• 81
3k views

### Why aren't ferrite rod antennas used in WiFi?

Does it have something to do with soft ferrite's low coercivity, still not low enough at gigahertz frequencies? See, I'm putting together high gain receiver antennas and transmitter antennas. Space ...
• 279
5k views

### Why does a real world capacitor behave like an inductor at frequencies above its self-resonant frequency?

I've come across some graphs comparing the impedance of a capacitor over frequency and it understandably declines as frequency increases -- up until a certain point. Afterwhich, the impedance begins ...
• 777
30k views

### How fast can a transistor switch?

An NPN transistor can be made a switch by applying some power to the base. Is there a limit to how fast I can switch the transistor on and off, or I can switch it on and off as fast as I can turn the ...
• 189
2k views

### Is it true that the power line frequency is kept accurate by atomic clocks?

I've heard rumors that the power line frequency is kept stable and accurate by syncing it with atomic clocks. Is this true? What kind of accuracy does it have? Is this true everywhere?
• 28.7k