Questions tagged [impedance]

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.

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55 views

Transformer secondary coil impedance [closed]

To transfer maximum power from the secondary coil to the load, I need to find secondary coil impedance. My load impedance 5 - J365. I would design a matching circuit between load and secondary coil, ...
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Impedances inside transmitter?

A 50 ohm match can be tricky outside a transmitter to match. One has to deal with ensuring the antenna , coax, and all connectors are all equal or close to the output impedance of the radio. Let ...
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Will measuring SWR through a feed line mislead me?

I know that except in the perfectly matched case, transmission lines transform impedances along their length; if I measure the impedance at the other end of my feed line, or even with a short jumper ...
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Do stub matching techniques still produce some loss?

I am using a double stacked Yagi-Uda antenna with about 57 Ω impedance. The 50 Ω feed line (coaxial) cables are combined using a tee connector. I observed, at the output of the tee connector, an ...
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Wideband impedance matching

I'm using an antenna that works in the range from 1 GHz to 3 GHz. I want to match impedances between a cable from the transmitter and the input amplifier and from the output amplifier and the cable to ...
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Stub impedance matching

What is the process of stub impedance matching and what are the elements included in the calculations relevant to it?
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Quarter Wave Transmission Line transformer

Can someone explain to me exactly how a quarter-wave transmission line transformer is put into action? I mean, how does it operate and what values are usually taken into consideration, calculation ...
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Coaxial Folded Dipole Antenna Matching Impedance

In http://www.nsw.wicen.org.au/technical/projects/coaxial-folded-dipole-antenna, the guy is using a 50 ohm coax cable to build a folded dipole antenna and claims that this will enable use at 50 ohm (I ...
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What is the impedance of a 1.25 λ dipole antenna?

I would like to make a dipole antenna. This particular antenna is used for reception only; no transmission is involved. I would like to receive as much power as possible by this antenna as it is used ...
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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 ...
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What's the difference between “minimum SWR” and “resonance”?

Is the point of minimum SWR equivalent to resonance? Exactly what does resonance mean, anyway?
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Impedance Matching Different Feedlines

(I promise there will be a question in this wall of text. I'm just giving context.) I've been wanting to try my hand at building my own antenna system for the last few weeks and in doing research, a ...
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Resistive impedance with frequency

Full disclosure, I'm a little dyslexic. Concepts that are easy to most people usually seem ambiguous to me. I also have a had time expressing myself through writ so please forgive me if this seems ...
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Reciprocity and SWR [duplicate]

If someone has a high SWR, obviously their signal will not make it out as far due to reflections. However, they will still be able to hear relatively well. I have noticed for receive, a high SWR may ...
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What happens in a low loss feed-line with a high SWR

I was recently reading an interesting article from the ARRL to get a better understanding of the SWR. The following case is still unclear: A low loss feed-line with an impedance that doesn't match ...
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Why is the risk of damage to a transmitter due to a mismatched antenna at lower frequencies greater?

A quick follow-up to this answer ... If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies ... I'm sorry to be so dense, but uh why is the risk ...
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How does inductive base loading cause low feedpoint impedance in verticals?

As an extreme example, take mobile HF antennas. These can have very low feedpoint impedances, maybe as low as $6\Omega$. The ideal impedance of a quarter/wave vertical is $36\Omega$, but electrically ...
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Should the capacitance or inductance be varied to achieve resonance?

A resonant circuit is typically composed of some resistance and reactance, the latter being provided by inductors and capacitors. The resonant frequency being calculated as the inverse square of their ...
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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?
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Using wirewound resistors in a dummy load

I have a bunch of high-wattage 50 ohm resistors lying around, but they are wirewound. If I use them as a dummy load for transmitters 144 MHz and down, how bad would that be? Since they probably will ...
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Is the bandwidth of an LCR resonant circuit independent of the capacitance?

Is the bandwidth of an LCR resonant circuit independent of the capacitance, if the inductance and its series resistance are kept the same, and the Q is high? This question and the calculation ...
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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 ...
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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 ...
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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 ...
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What impedance matching do I need between my 300Ω feedline and Softrock receiver?

I will be assembling a Softrock Ensemble II HF receiver, and I know I'm going to want it on air as soon as I build it, so I'm challenging myself to build an antenna for it first. The plan is to do a ...
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What is the point of a SWR/power meter where the needles cross over each other?

There are SWR/power meters with two separate gauges, and others that have them mounted so the gauge needles cross over each other. Aside from looking cool, does the cross-over point of the two meters ...
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583 views

Tuning an antenna with a SWR meter that relies on output power

In my (new) setup, I will have a solid-state HF radio driving an antenna through an antenna tuner. Both my radio and the antenna tuner have internal SWR meters, of the type that requires you to adjust ...
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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 ...
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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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When and how do I use a Smith chart? [closed]

What are some real-world problems that a Smith chart can help me solve? Ultimately I'd like to gain a more intuitive understanding of the space the chart represents, but it seems to me that actual, ...
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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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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?

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