# Questions tagged [wavelength]

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### Ultrasonic phased array speaker spacing for high directivity and efficiency

(Short version of question(s) below.) I want to make an ultrasonic parametric speaker at 40kHz, I want to drive them all at the same constant frequency to keep the electronics cheap. When simulating ...
• 143
35 views

### How to change the wavelength of LEDs in Proteus?

I have a problem in designing a circuit for my project. Can anyone explain how to simulate an LED with 940, 1550, and 1650 nm in Proteus software? Dors the emission coefficient of LEDs in Proteus help ...
49 views

### Why does short band (high frequency) radio travel longer than low frequency?

In physics, we are taught that longer wavelength (lower frequency) have a lower attenuation in air, and thus is able to travel longer distances. However, when talking about radio channels, short wave (...
1 vote
78 views

### How to calculate far field distance from an antenna

I understand the formula for calculating the far field distance from an antenna is: Distance = (2D^2)/λ Is the D in the above equation the length of the antenna under test (antenna under test is a ...
• 340
52 views

### Tuning current limitation for VCSEL laserdiode

Recently, we have bought a VCSEL laser diode, in which we can vary the wavelength by tuning the voltage and/or tuning current. Also, we got an application note in which it states as follows: "Set ...
• 93
2k views

### What is the meaning of "longer electrical length = more wavelengths"?

Reading a Keysight-note, not sure what is the following selected line means? I read and understood the meaning of electrical length, how it is related to bit in flight and wavelength is not clear.
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383 views

### Why dimension of antenna's elements can be 1/2 and 1/4 or wave length and what about 1/3 or 1/8?

I'm an amateur and looked to the calculators of TV/3G/WiFi antennas. All articles state I can get away with all sizes divided by 2 or 4 (for biquad antenna & the range 400MHz - 2.1GHz dividing by ...
• 375
1 vote
162 views

### Reflection in low frequency conductors (not transmission line)

Is the reflection phenomenon common in RF work with unmatched source/load pairs also present at low frequencies? Or are the wavelengths so much longer than the physical conductor lengths that ...
• 576
93 views

### How do we tell distance to target at the receiver from frequency modulation?

Was thinking about radar and how to tell distance using FM. If you send a wave with a consistent wavelength of 1 meter, and it hits a target 1000 meters away and then comes back, it will have gone ...
• 31
126 views

### What is the impedance looking into a length of coaxial cable that is short-circuited at the far end and a half wave-length long?

What is the impedance looking into a length of coaxial cable that is short-circuited at the far end and a half wave long? I have been told that this the the basis of what is known as a wave guide &...
103 views

### What technique (ultrasound/infrared) should I use to detect seeds inside a fruit? [duplicate]

This fruit is simplistic as there is a thin skin surrounding it. Inside it is a tiny ball of liquid and that is where the dense seed forms. The is seed much more denser in comparison with the liquid ...
180 views

### With so much radio signalling occurring simultaneously (TV, Cellphone, Radio, etc.), how does our atmosphere keep them separated and avoid disruption? [closed]

I know this question has been asked before, but I still don’t completely understand. I understand that different stations are given different frequencies, but waves are able to interfere with each ...
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### Antenna conterpoise or ground plane. Confused about length requirements

I have an appliation where i need to mount a multiband (VHF/UHF/700/800/900 MHZ) mobile antenna (picture 2) on a tower. The spec sheet for the antenna says it used a 4 foot diameter ground plane for ...
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1 vote
57 views

### Antennas- Spacing between Reflectors & Directors in Wavelengths

I’m building an antenna and I want it to connect to channel 6 on the spectrum allocation chart (2.437 GHz). I’ve calculated the lengths of the reflectors and directors but im just a bit stuck on the ...
• 273
1 vote
85 views

### Selection of wavelength for optical reflective sensing

Most of the reflective sensors in the market use either red or near IR wavelength and have a very short range (in the range of mm). Given the reflectance of the Si at different wavelengths and ...
65 views

### Plotting a 20 MHz RF wave in Excel

How can I plot "F1(t) = 20MHz" in Excel? I will eventually put it into mathcad. The amplitude would be a variable as well but lets pick 4.5 for now. Just get the 20 MHz wave to look how it should. ...
126 views

### Why does lumped discipline not hold as dimension approaches operating signal wavelength?

I'm studying some basic introduction to the lumped matter discipline on my own. I completely understand where the first two constraints come from (i.e. lumped matter can only interact through their ...
• 33
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### How can a non-sine waveform can equate to combination of DC voltage?

It has been found that any repeating, non-sinusoidal waveform can be equated to a combination of DC voltage, sine waves, and/or cosine waves (sine waves with a 90 degree phase shift) at various ...
9k views

### Why does 1/4 wavelength have a ground plane and 1/2 wavelength needs none?

Why does 1/4 wavelength have to have a ground plane and 1/2 doesn't? I know that an antenna that has half a wavelength does not need the ground plane (example a dipole antenna) and when using a ...
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