Questions tagged [math]
Questions which may involve math, including calculations about signal levels, the math theory of certain modulations or modes, or anything else.
35 questions
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Calculating SWR for a dipole
I have a dipole wire antenna that is tuned to 14.0 MHz so that it has an SWR there of nearly 1:1. Is there a mathematical formula by which I can compute the expected SWR for other frequencies? I would,...
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Why is the total radiated power of array calculated by sum of square of excitation coefficients different from the result by integral of power pattern
Consider an array with same isotropic antennas, $P_{ele}^n$ is the input power of the nth antenna. As I consider antenna radiation efficiency = 1, the $P_{ele}^n$ is also the radiated power of the nth ...
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How does IQ modulation work (intuitively)?
I'm trying to get my head around IQ modulation. What I understand so far is that each of the I and Q branches of the mixer produce two sidebands with the same frequency components, but in the Q branch,...
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Adding and subtracting dB/dBm/dBi values
I've got a question and any clarification on that would be greatly appreciated.
For calculating the pathloss in wireless communication we usually use the following formula:
PL = pathloss (in dB) + ...
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The HPBW of a helical antenna
can someone tell me what are the formulas of HPBW for a helical antenna?
I've searched a lot and I saw that there are two different formulas of HPBW for the helical antenna,
this one,
$$ \mathbf{(HPBW)...
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FT8 callsign/maidenhead compression encoding
I have set myself a challenge to write a Matlab script as proof of concept to send an FT8 CQ call (not necessarily for live transmissions yet, but I may extend the project). So far I have:
Generated ...
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Solid angle for different E/H plane beamwidths
The solid angle formula calculates the surface area on a unit sphere, from projecting a rectangular patch onto the surface of a sphere.
Image source
This is calculated using the azimuth angle $\phi$ ...
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Why EME with 100W and a single Yagi-Uda antenna is possible?
Recently I've been reading about EME and there was one thing that surprised me. Many sources claim that EME has path loss for 2m band about 252 dB. In the same time they claim (one, two):
Recent ...
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How to calculate VFO/IFO frequencies?
I am trying to build a simple superhet receiver for listening SSB signals.
I read several articles about SSB and got confused so I am looking for some practical explanation.
I have 2 mixers, quartz ...
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dBm signal minus dB
I've got a 27dBm signal that I'm going to put through a 6dB attenuator. How do I work out the resultant signal in dBm?
I've tried Googling that without any luck.
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Exactly why do some SWR meters give a changing reading depending on the length of coax used to connect to an antenna?
Following is my understanding of some theory and the questions are at the end.
Is this right ? ...
A standing wave is an AC waveform oscillating at a particular frequency which has a varying ...
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How can the voltage at the center of a resonant half wave dipole be zero if the input impedance is 75 ohms?
If the input impedance of a resonant half wave dipole at the feed point is 75 + j0 ohms, then if an AC sine wave voltage V is applied to the feed point, how can the voltage at the center be zero ? ...
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The right antenna size
I'm preparing for the USA Technician exam and I was reading in the manual that the ideal size for a dipole is following this strange formula: 1/2-lambda. But based on what I read after, it seems it ...
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What is the equation relating maximum data transfer rates for a given EM bandwidth
I was thinking, since visible light has a much higher EM frequency than radio wave light, its bandwidth also has a far higher max data transmission rate, so people have been researching how to use ...
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How to decode a message with unknown bit rate in interstellar signal
I have a question about FSK modulation I'm going to frame in terms of a hypothetical:
Imagine that you are transmitting a message to an ET in another solar system. The message is encoded in binary ...
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