Impedance is the measure of the opposition that a circuit presents to an alternating current when a voltage is applied. This is a force of much interest to the radio amateur especially surrounding the connection to antennas.
Questions tagged [impedance]
102 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, sometimes I want a wide band antenna just for…
K9KRB
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Why do I need to tune an antenna?
I've heard that when an antenna is set up, it needs to be tuned to reduce reflective power back into the radio. Is this always necessary, and if so how would I go about tuning it?
berry120
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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?
Bill - K5WL
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How does an SWR meter really work?
For ham radio operators, the SWR meter is a ubiquitous piece of equipment. There are dozens of standalone models on the market and most modern transceivers and antenna tuners have this functionality built in.
Any ham with an interest in antennas has…
Glenn W9IQ
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Understanding coax impedance
I keep doing research, and trying to grasp it, but when it comes to RF impedances, and coax, I still have trouble trying to grasp it.
So first, I think you have to have a 50 ohm coax for a 50 ohm transmitter to keep the impedances matched. I think I…
Skyler 440
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How can I safely transmit without an antenna tuner or SWR meter?
Just what the title says.
An Antenna Tuner, henceforth AT, is almost a de facto piece of equipment in a shack; working the bands without one is tantamount to leaping off the diving board into a swimming pool with tarantula nests in it ... or…
VU2NHW
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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.
$D_a$: The diameter of the radiating element of…
Robert Quattlebaum
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Why does ice on a wire dipole affect the SWR?
We just had snow and ice overnight and my wire dipole was coated in ice. Why does the ice covering negatively affect the SWR of the antenna?
Ron J. KD2EQS
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How does an antenna transform impedances along its length?
If I insert some impedance (like a loading coil, or a trap) at the base of a monopole antenna, the effect on the feedpoint impedance is easy to predict: the impedance is in series with the antenna, so whatever the feedpoint impedance was, the added…
Phil Frost - W8II
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Why does "high SWR" damage transmitters, instead of "impedance mismatch"?
In the audio realm, where cable lengths are insignificant compared to the signal wavelength, I would understand an impedance mismatch damaging an amplifier as follows:
Take an audio amplifier that can deliver 100 watts of power into an 8 ohm speaker…
natevw - AF7TB
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What is the actual loss in a feed line with high SWR?
It is well-known that it is unwise to have standing waves on the feed line between one's antenna and one's transmitter, unless it is a very low-loss type (e.g. ladder line), because the transmitted signal is reflected multiple times through the feed…
Kevin Reid AG6YO
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Why are there so many coaxial cable impedances?
Why do we have 50, 75, 62 and 92 Ω coaxial cable, to name a few? Why not just one standardised cable? Is there some technical reason or did Mr. Coax and Mr. Cable have a disagreement, like Mr. Tesla and Mr. Edison?
R Johnson
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How do I design a round or square coaxial transmission line to have a specific impedance?
Certain Hex Beam antennas use a coaxial center support post to send the RF to each antenna section, which is superior, in terms of maintenance, to a post with screw terminals connected by short lengths of coax used in previous designs.
I'd like to…
Adam Davis
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If two antennas of 50 Ω and 377 Ω have VSWR=1:1, then which one is more efficient?
If there are two antennas of 50 Ω and 377 Ω (same as the intrinsic impedance of air) impedance with 0 $\Omega$ ohmic resistance, and they are exactly matched with their transmission line, then which antenna is more effective in terms of radiating…
kaka
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How is a 1:1 current balun different from a choke?
I have a 10m dipole and am going to feed it with 50 ohm unbalanced feed line (coax). My understanding is the feed point of this style antenna is about 50-75 ohms, and since it is a balanced antenna I'm thinking I need some type of balun. I'm…
Java42
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