Questions tagged [antenna-theory]
Designing antennas, selecting antennas for specific applications, properties of a given antenna design.
490 questions
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What is the relationship between SWR and receive performance?
If an antenna analyzer shows 1:1, does that mean it's an ideal receiver as well? And what about the converse, will a well performing receive antenna show a 1:1 SWR?
I've wondered this for a while, ...
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How do Handheld antennas work without ground?
Dipoles have the 2 wires going to each leg of the antenna completing the circuit.
Big AM towers use the second wire as a ground plane
But how do handheld rigs transmit and receive with just one wire ...
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How does the signal know where the cable ends and the antenna starts?
I know very little about antennas. I know, that for a certain frequency the antenna needs a certain lengths for good sending/receiving conditions.
Often the antenna is at the end of a cable. Why doesn'...
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What is the peak voltage at the tips of a dipole antenna?
What is the peak voltage present at the very end tips of half-wave dipole antenna in free space, and how might this peak voltage relate to transmitter type, transmitter power, RF frequency vs. antenna ...
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Why do folded dipoles have greater bandwidth than ordinary resonant dipoles?
This is something I've read in passing, but never encountered an explanation of why. For example, Wikipedia says:
Another common place one can see dipoles is as antennas for the FM band; these are ...
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How does a mag mount antenna achieve a ground plane?
I've been thinking for some time about magnet mount mobile antennas and wondering how they establish their ground plane. Consider that many mag mount antennas have some kind of protective coating on ...
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3
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Why do amateur radio operators call an RF choke a balun?
When using a balanced antenna such as a half wave dipole, with an unbalanced feed line such as coax, an RF choke can be used to block RF current emitted by the transmitter from splitting up at the ...
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How does moving a feedpoint off-center in a dipole affect the resonant frequency and resistive load?
Specifically, I understand that OCF dipoles change the SWR, but does it do this via reactance or resistance, or both?
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What is a "random wire antenna"?
Some antenna tuners claim to match any “random wire” to any HF frequency. Can one really use a random wire as a practical antenna system?
From everything I have heard, the resonance of the antenna (...
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4
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What does the addition of a shield to a small loop accomplish?
A small shielded loop is an antenna with a loop of wire, smaller than 1/10th of a wavelength in diameter, also surrounded by a shield. Often, they are constructed from coax. There is a gap in the ...
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What is the impedance of an end-fed half-wave antenna?
It is my understanding that the feed-point impedance ($Z_a$) of an end-fed half-wave antenna is dependent on at least the following factors:
$L_a$: The length of the radiating element of the antenna.
$...
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Calculating Antenna Length on the FCC Exam vs. in Reality
I have seen the following formulas for calculating half and quarter wavelength antennas:
Formula for $\frac{1}{2}$-wavelength antenna (in free space):
\begin{equation}
\mathrm{Length~(feet)} = \frac{...
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How does a folded dipole work?
A folded dipole is like an ordinary dipole, but with the ends extended and folded back, until they meet. Although it looks like a loop, I'm told it behaves similarly to a dipole.
How does this thing ...
13
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Conductive boom vs non conductive boom: what's the difference on a Yagi?
I designed a Yagi antenna using 4nec2, assuming that I would use a non conductive boom.
If I use an aluminum boom but I insulate the elements from the boom, can I keep the same design? How does it ...
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Are antennas circuits?
For an antenna to work, doesn’t charge have to flow through it? A current must be present. To me it indicates it must be a circuit, but how is a dipole a circuit?
If they are not circuits, then how ...
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