What is High frequency: Definition and 86 Discussions

High frequency (HF) is the ITU designation for the range of radio frequency electromagnetic waves (radio waves) between 3 and 30 megahertz (MHz). It is also known as the decameter band or decameter wave as its wavelengths range from one to ten decameters (ten to one hundred meters). Frequencies immediately below HF are denoted medium frequency (MF), while the next band of higher frequencies is known as the very high frequency (VHF) band. The HF band is a major part of the shortwave band of frequencies, so communication at these frequencies is often called shortwave radio. Because radio waves in this band can be reflected back to Earth by the ionosphere layer in the atmosphere – a method known as "skip" or "skywave" propagation – these frequencies are suitable for long-distance communication across intercontinental distances and for mountainous terrains which prevent line-of-sight communications. The band is used by international shortwave broadcasting stations (3.95–25.82 MHz), aviation communication, government time stations, weather stations, amateur radio and citizens band services, among other uses.

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  1. M

    B High Frequency Photons: More Mass, More Bend?

    Since high frequency photons have more relativistic mass, should we expect them to bend more than lower frequency lights when traveling through a gravitational field, thus produce a rainbow effect? But we don't seem to experience rainbow effects with star light.
  2. M

    Amplify ferrite core solenoid electromagnetic range

    Hello all, I'm playing around with a PIC + LCC Tank to send - at a 5MHz frecuency - some numeric data via BPSK. The receiver is a loop antenna placed in the ground. The sender antena (L) is a ferrite core solenoid (N=10). As having a larger core, or increasing the Number of coils around the...
  3. R

    What Are Some Options for High Frequency EMF Meters?

    Hello all, I don't know if this is the correct place to post, but I'm looking to detect all electromagnetic waves around me that have a frequency that is under the visible spectrum. The reason is to try and get some kind of idea of what kind of radiation is around me, so that I can be more...
  4. Lnewqban

    Study about high frequency mosquito flight

    Please see article here: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5412966/?report=classic
  5. N

    High Frequency Linear Array BeamForming

    Hi all I am doing some research on High Frequency Linear Array beam forming (for imaging sonar). For that purpose, a linear Rx Array of 100 channels have been constructed with inter channel spacing of 14.3mm. A transmitting Tx probe operating at 420 KHz (approx. 300 cycles CW pulse) is placed...
  6. D

    Can a Coiled Antenna Receive Radio Signals at 30 MHz?

    if an antenna 8.2 feet long was coiled up into a coil could it still receive radio signals at 30 megahertz?
  7. A

    Help with LTSPICE on a high frequency circuit

    Hi, can you please tell me how would I be able to determine the effectiveness of a specific circuit, see in the attached spice file I tried to simulate a circuit , my secondary side is a self generating coil which in spice I had to simulate with mutual inductors aka a transformer, my basic idea...
  8. A

    Active power dissipated by a resistor from DC to RF

    Hello all PF members! I was wondering about the power dissipated by resistor at high frequency which is: ##P=Re\left \{ U\cdot I^{*} \right \}=Re\left \{ \frac{\left |V^{+} \right |^{^{2}}}{2\left |Z_{c} \right |}\cdot (1-\left |\Gamma \right |^{2} )\right \}##, (1) where: ##Z_{c}## -...
  9. A

    Core material for high power high frequency coil/solenoid

    I read the limits of typical ferrite cores and it seems that most sources claim that they tend to work somewhere up to 1 Mhz. Surely they work great under that frequency, but is there any material that could provide a core material for a wide frequency range starting from few tens of Khz up to...
  10. S

    I Running through a complex math derivation of plasma frequency

    Background of problem comes from Drude model of a metal (not necessary to answer my problem but for the curious): Consider a uniform, time-dependent electric field acting on a metal. It can be shown that the conductivity is $$\sigma = \frac{\sigma_0}{1-i\omega t}$$ where $$\sigma_0 =...
  11. M

    High frequency in MEMS devices

    Hello, I am designing a resonant mems accelerometer. It has a resonating beam. We are actuating it by AC voltage + DC voltage. We are going to actuate it at beam's resonance frequency. When I search for papers related to previous studies, I encounter resonance frequencies ranging from 20 kHz to...
  12. Exidor

    Trouble with high frequency astable multivibrator

    I am having trouble getting an astable multivibrator to oscillate higher than 480 KHz. I added a "baker clamp" which gave some improvement, but didn't get me to the target frequency of 816.5 KHz. I am on an iPad and can't post a schematic. I use 2sc6082-1e transistors and bat41 diodes for the...
  13. mertcan

    Can Maxwell's Method Be Used for High Frequency Circuit Calculations?

    Hi, initially I have seen that when circuits are exposed to high frequency kirchhoff laws become invalid. According to my search I can not find any derived circuit equations for that case, instead computational electromagnetism method is suggested using maxwell. Is it the only way to make...
  14. R

    Electrical How to build your own high frequency oscilloscope

    Does anyone know if there is a textbook on the design and construction of high frequency oscilloscopes (up to 10 GHz)? I am guessing they would be some form of ADC circuit with perhaps a mixer and could use a lap top as the "DSP" and display. How would such an O-scope be calibrated/tuned...
  15. blainiac

    High Frequency Electromagnet Possible?

    I was wanting to build a very high frequency electromagnet to test an idea and it requires something in the range of about 1-10 GHz, and I'm unable to find much information on what I'm attempting to do. I understand the impedance will be incredible, along with some other technical issues. Most...
  16. D

    High frequency being transformed to a low frequency

    Hi Physics, I have an idea but before i start. I must know am I right. Is it possible? We have a small room with two objects. The first object is a producer of sound waves out of the human hearing range. This object sends ultra sound waves to the second object. The second object start to...
  17. A

    High K material in High frequency

    Hello all I need a high K material to cancel out E-field in some direction (induced by electromagnetism). This high K material (above 5000) must work in high frequencies above 10MHz. I did use the ceramics but there is no clue that it will work in that range of frequencies or not. I am really...
  18. Manolis

    Driving a neon bulb with high frequency

    I want to produce a 100 volt peak to peak symmetrical AC waveform to light a miniature neon bulb. It strikes at about 90 volts then settles ("clamps") at about 50 volts, according to the spec. I want the frequency to be at least 10 kHz for easy filtering because the circuit will also be passing...
  19. C

    Open Circuit Termination for Waveguides in High Frequency Labs

    Hi everyone, I am trying to understand that why do we use open circuit terminator for wave guides or any RF element such as coupler and etc. I know if we just leave it open, it does not work as open circuit. But why?
  20. Destroxia

    Planck's Law: Low, and High Frequency Limit

    Homework Statement a) Derive the Rayleigh-Jeans distribution by taking the low-frequency limit of Planck's distribution. b) Derive the Wien distribution by taking the high-frequency limit of Planck's Distribution. Homework Equations ## u(f) = \frac {8 \pi f^2} {c^3} \frac {hf} {e^{\frac...
  21. Planobilly

    How to select a ferrite bead to suppress high frequency

    Hi guys, I see ferrite beads used on the input of V1 on some high end tube guitar amp designs without any indication of type and value. Can you give me some idea how to select this component and at what other places in a tube amp it could prove useful? Thanks, Billy
  22. N

    Troubleshooting a High Frequency Mixer: Oscilloscope Output Analysis

    Hi all, I am making a frequency mixer to add together channels of an amplifier I have at 52.892kHz. I am attaching a picture of the schematic and the physical circuit I made along with the output on the oscilloscope I am measuring. Instead of the three outputs shown in the schematic, I am just...
  23. W

    B Simple probability with high frequency

    I'm trying to remember simple probability form high school. I'd like to know how the probability of anyone event changes with frequency. So for example the probability of getting one ace of spades is 1/52; what is the probability of getting at least one ace of spades if the card is put back and...
  24. J

    Phonons driven at high frequency

    Homework Statement For one-dimensional monatomic crystals, the dispersion plot for phonons has a maximum frequency ωmax. If a driving force oscillates the crystal beyond this frequency, the phonon will no longer propagate and will instead decay as it gets further from the external source of...
  25. debajyoti datta

    High frequency behaviour of copper

    Will copper behave as a dielectric in high frequencies?...I tried to answer the question with loss tangent but relative permittivity of copper posed a problem...everyone on internet opines differently about relative permittivity of metals...then I looked at skin depth which decreases with...
  26. Chris Wallin

    A HF pulsed UV light effect on metal alloy

    I'm trying to understand the effect on a metal alloy of UV light (diode or laser) pulsing at about 1MHz. I am assuming that the stirring of atoms will generate heat, possibly moving the alloy to its eutectic point (depending on the alloy) and in particular to atomic motion. Can anyone...
  27. M

    High Frequency that can cause g-sensor damage

    Hello All, Anyone can help, but first allow me to give you some background, I have a project this project is to measure the frequency of the PCB depaneling machine that might damage the sensetive component which is the gyro-sensor. The sensor will damage if the frequency is above 75kHz or 100...
  28. A

    Varied frequency power supply for strobe light

    I'm looking to build a varied, high frequency power supply for a strobe light. Any suggestions on the best way to go about this? I would prefer to have it computer controlled so that I can change the frequency without manual input. Any pointers would be really appreciated! Thanks!
  29. avito009

    Does loud voice mean high frequency?

    As I know: Velocity of sound = wavelength x frequency. If frequency increases wavelength decreases. So even if you shout loudly the velocity of sound won't change only that you will hear a louder voice. So does that mean that louder voice has higher frequency?
  30. baby_1

    High Frequency Transistor Tutorials

    Hello As I read all the above links of Wikipedia about HEMT I have many problems to know better about these kinds of transistor.could you introduce me a good tutorial about HEMT transistors? Thanks
  31. C

    Wide bandgap semiconductor -- why higher temperature tolerance?

    I was wondering if anyone knows the relationship with temperature and frequency tuning in wide bandgap semiconductors. I just want to know why wider bandgaps have higher temperature tolerance and why does that mean high frequencies can be achieved? Explanation with formulas would be great!
  32. I_am_learning

    Absurdly high Frequency resolution of function generators?

    I checked some common commercial high-quality lab function generators and they seem to provide frequency output upto 50 Mhz (not a big deal), but with resolution of 1 uHz ! That means, they can generate signal with 50000000 Hz and also with 50000000.000001 Hz ?? That would equate to time-period...
  33. E

    High Frequency Servo shielding and grounding on robot?

    I have an issue that appears to be relating to noise mitigation and grounding. Some background on myself is I have a mechanical engineering technology degree. But my job requires an ability to work with and troubleshoot electrical issues. Currently a customer is using a Servo motor on an end...
  34. G

    High Frequency signal with fast risetime, its bandwidth

    Hi, I am new to world of electronics and to high frequency Domain. But I am working on a design where I have a coax of 30cm length. I have used an external oscillator to generate 7GHz fast falling pulse. I am using a Controller to control the oscillator. Now I have a pulse of about 350ns...
  35. B

    Create High frequency High voltage signal

    Hi all, For my research I would like to create a high frequency high voltage signal. This signal should be in the order of 1kV-5kV with a frequency of around 10MHz. Can anyone help me with this? I'm not an electronic expert. I only have to apply the electric field, please note that I do not...
  36. T

    Help with high frequency measurements

    Hello everyone! So I am currently working on a project involving classroom equipment from PASCO. (http://www.pasco.com/prodCatalog/WA/WA-9314_microwave-optics-basic-system/#overviewTab) What I'm working on is not exactly related to the the classroom project but closely related to the...
  37. D

    Low and High Frequency Signal Equivalent

    Homework Statement Assume λ≠0. Also bypass capacitor is very large compared to coupling capacitor. a.) Draw the low frequency small signal equivalent and derive lower 3dB frequency formula. b.) Assuming transistor high frequency capacitances, draw the high frequency small signal equivalent and...
  38. E

    Learning GRT: Why the High Frequency Search?

    I am trying to learn GRT so I can answer questions for myself. But I might croak first, so I’ll ask here. That gravity wave interferometer they are building out in Richland, Washington - I obviously haven’t read all the technical papers on their web site, but I am pretty sure one I did read...
  39. G

    High Frequency Versus Low Frequency

    Please correct me if I am wrong in anything below, including clauses. i was trying to find a simple explanation for the frequency and i come up with this , 1) Frequency (Hertz(or s^-1)) = 1/ T (Seconds) F = 1/T => T (seconds) = 1/ F(s^-1) 2) "Place A" is 338 Kilometers away from "Place B"...
  40. A

    Generating a pulse of high frequency and very small duty cycle

    Hey, I wanted to generate a pulse of ON time of about 10-50 ns and time period of around 1us. Don't know how to get such precision ? Thanks
  41. A

    Unable to send current through high frequency transformer

    I am building a transformer of about 9.3 gain operating at 20kHz. One would think this is saturation but if that were the case there would at least be some voltage across the load. The gain of the transformer is as expected for no load conditions but I cannot get this same voltage across a load...
  42. E

    Differential pair, current mirror: high frequency analysis

    Hello, I have a doubt about the high frequency response of the MOSFET (or BJT as well) differential couple in the case it's polarized by a current mirror. Here's a picture of my issue (it shows the semi-differential circuit of a MOSFET differential couple with a "small" common mode ac input...
  43. A

    Producing Alternating current of high Frequency.

    As the title suggests, how are very high frequency AC produced? A AC generator must have a limit to the rotation velocity of the coil, mustn't it? Any help would be appreciated. Thanks.
  44. G

    Charging a Capacitor with High Frequency DC voltage

    Hello All, Could you please explain what would happen if I charge a capacitor with say 30 khz DC 500 volts with a 10000 uf cap. Would a gas discharge tube, varistor, triac of 300 volts connected across the capacitor help to preventing it from exploding? Ged
  45. S

    High frequency noise in smps transformer

    I have assembeled one smps circuit for 25volts, 40 amps. Circuit gives unwanted high feaquency noise at part load. It is silent at no load. What could be the problem. I am not electronic engineer, Electronics is my hobby. Any body can help me.
  46. A

    MOSFET for High Frequency Low Current Application

    Does anyone have some recommendations for MOSFET's that can be used for high frequency low current applications? The ones I found are for high current applications but my application only requires at max 20mA. Thank You.
  47. A

    Use of high frequency in communication

    can anyone tell me why do we use high frequency in communication? why we can't just use low frequency signal for these ?
  48. S

    How did Tesla create such high frequency currents?

    I've read his book and he talks about AC current frequencies of incredibly high magnitudes. How was this achieved? Surely he did not just spin his dynamo really, really fast.
  49. P

    Why does low frequency light appear to travel faster than high frequency light?

    I understand that new findings from the 'magic' telescope, suggest that higher frequency light arrives earlier than low frequency light. The results have been taken from a light source that is very far away. apparently this shows that spacetime is not uniform and that higher frequency light...
  50. A

    Generating High Frequency Signals

    What is the best way to generate a signal with a high frequency (700 MHz - 30 GHz)? Is there a preferred circuit diagram for such a design, or is it better to use a processor of some kind? Is it really heavily based on the length of the antenna (dipole)? I am trying to do it as cheap as...