Questions tagged [wavelength]

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How large is difference in range between LoRa devices on different frequencies?

I recently bought Lilygo T-Beam device with frequency 923Mhz for my country. I wonder if there is some big difference in usable range (in km) between low and high ...
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1answer
46 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 ...
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5answers
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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2answers
187 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 ...
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2answers
128 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 ...
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1answer
91 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 ...
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1answer
102 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 &...
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2answers
102 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 ...
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2answers
177 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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1answer
93 views

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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1answer
53 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 ...
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2answers
79 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 ...
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2answers
60 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. ...
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2answers
99 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 ...
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1answer
63 views

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 ...
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4answers
8k 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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2answers
239 views

Lumped parameter vs transmission line model for a piece of cable

I would like to model a piece of cable (less than 5m) over a frequency range of DC to \$1\mathrm{MHz}\$. I am however doubting if I can approximate it by a lumped parameter model (mainly at \$1\mathrm{...
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0answers
184 views

Wavelength on microstrip line

I am trying to calculate the wavelength on microstrip transmission lines. From what I have understand I should use the following relationship: \$ l = c/(f*\sqrt(Er))\$ where Er is the dielectric ...
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1answer
202 views

Blocking RF on same side as PCB antenna?

I have a penta-band GSM transciever on a 4-layer board, along with a matched chip antenna. Similar concept to EE.SX/questions/35836/how-do-components-on-a-ground-plane-of-monopole-pcb-antenna-effect-...