# Questions tagged [frequency]

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

997 questions
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### 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 ...
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### What's special about 14.31818 MHz?

While desoldering useful components off of old computer hardware, I found quite a large number of 14.31818 MHz crystals. This seemed odd to me. Why use such an irregular frequency with a very ...
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### 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 ...
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### Can I turn Radio waves into light?

Wikipedia says that the frequency of light is 300 THz. I've made a radio waves transmitter that transmits about 100 MHz. If I increase the frequency of the transmitter to 300 THz, will the antenna ...
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### 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 ...
14k 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 ...
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### 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 ...
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### 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 \...
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### 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 ...
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### Why do push button telephones use dual-tone for signalling?

Here is a related information from wikipedia: For touchtone service, the signal is a dual-tone multi-frequency signaling tone consisting of two simultaneous pure tone sinusoidal frequencies. ...
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### Why is a lower switching frequency more efficient?

I'm designing a 10V to 3.3V step-down converter. Looking at the LT8610, the applications example shows two similar circuits that have different switching frequencies. The Efficiency vs Frequency plot ...
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### 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 ...
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### Why do digital scopes sample signals at a higher frequency than required by the sampling theorem?

In the quest for a not so expensive PC scope/logic analyzer, I have found a nice little device it looks very well done and I know it will do the job. However looking at the specifications, I ...
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### If an FM signal has different frequencies, how does the radio receive the signal in a fixed frequency?

If an FM signal has different frequencies according to the modulation, how does the radio receive the signal in a fixed frequency like 103.2 MHz?
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### Frequency limitation for homebrew CPUs

While looking into some custom built CPUs I've noticed the frequencies at which they operate are relatively low compared to modern CPUs (in the order of several MHz). Is there an electronics ...
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### 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 ...
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### How does RF anti-jam technology work?

I'm pretty certain that RF jammers work by overpowering the target signal with their own higher powered signal at the same frequency. So the question is, how does anti-jammer technology negate the ...
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### 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 ...
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### 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 ...
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### Is current with a frequency less than 1 Hz still considered DC?

We had a big argument last night with vague conclusions. Is the current with a frequency less than 1 Hz considered DC? It would still resemble a wave...
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### 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 ...
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### 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. ...
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### How can a phone wire have multiple frequencies at once?

How can a phone wire have multiple frequencies? In my Networks Textbook about DSL vs Dial Up it says the following: The residential telephone line carries both data and traditional telephone ...
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### Minimum Switching Frequencies in Boost Converters

Why are switching frequencies for boost converters above the 100kHz range? If I understand correctly, as the frequency increases from 100kHz upwards, the ripple current that is created from the ...
38k 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 ...
8k 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 ...
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### 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 ...
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### How is it possible to drive VGA displays at such high pixel clock frequencies?

I'm working on a digital circuit using discrete components to drive a 640x480 VGA display in a 80x30 text mode. For a 640x480 display, the pixel clock is 25.175MHz, which has a period around 40ns. I ...
32k 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 ... ...
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### 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 ...
1k views

### Estimate electrical frequency from clock shift

About 6 months ago I installed a solar power system with 2 Tesla Powerwalls for backup. Today, we got to test out the system with a power outage from an ice storm in the southeast. (We are still on ...
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### 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 ...
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### Is there a device that converts any AC frequency to 60 hz?

If I have something like a windmill generator that generates AC current, but at variable frequency, what device(s) would I need to convert that variable frequency into a constant 60hz frequency, so ...
1k 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?
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### 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 ...
1k views

### Why do spectrum analyzers use envelope detectors?

Spectrum analyzers can usually be represented by the following block diagram: Before entering the video filter, the signal passes through an envelope detector. What I don't understand is why this is ...
1k views

### Is the design decision for different frequencies in PAL and NTSC related to the AC mains power frequency?

In discussion a friend mentioned: In the original implementation of PAL and NTSC they used the AC current as a means providing the frequency for the TV. As the different mains had different ...
10k views

### What happens to RLC circuits at resonance frequency, conceptually

What occurs when $$\omega = \omega_r$$ The circuit frequency equals its natural frequency? So what. And why is it important?
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### What is the unit for resonant frequency?

What is the unit for resonant frequency? where $\omega_0 = \frac{1}{\sqrt{LC}}$? Is it just $HF^{-1}$?
886 views

### Why the resultant period of two signals is the LCM of the individual period of that signal? [closed]

Suppose a signal is constructed using two independent signals(say S1 and S2)both S1 and S2 have two different individual frequencies.The resultant signal that has been constructed has a new frequency,...
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### How susceptive is an inductor to frequency and current?

According to Coilcraft - Testing Inductors at Application Frequencies the inductance of a coil changes with frequency and current. Most datasheets don't give a frequency-inductance plot and current-...
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### Can LEDs or optocouplers be used without a resistor if PWM is used?

LEDs are often connected through a resistor and the purpose of this seems to be to lower the voltage across the LED to around 1.8V. Can PWM be used to lower the voltage instead of a resistor? If so, ...
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### Just how accurate is the frequency of US Wall Outlets? [duplicate]

I have a submersible pump for which I'm trying to determine the variability in flow rate, to high precision. Since this is just an impeller driven by an AC motor, what is the % error in frequency of a ...
1k views

### Difference between internal and external oscillator for a microcontroller?

I am a beginner with respect to microcontrollers, so I just want to ask is there two option for choosing the frequency of the microcontroller: to be internal or external? If there is internal ...
2k views

### 4 Hz Stable Frequency generator

Whats a good circuit/design that will generate a very stable 4Hz signal (to feed into a counter) that won't drift with temp / time. It's not so important that its exactly any particular frequency, ...
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 ...
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### 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 ...
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### What does it mean when they say 50MHz oscilloscope with 250MS/s sample rate?

I want to buy a digital oscilloscope to see how a WiFi module transfers signals and data. But I don't know which specification should I take into account? Actually I don't know what the difference is ...