# Tag Info

Accepted

### How does an SWR meter really work?

Dispelling the Myth To begin with, the typical HF SWR meter does not have the ability to separately sample the forward and reverse power, voltage, or current. Any description of the device or its ...
• 18.2k
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### Antenna Efficiency

In theory, if you had lossless conductors in the antenna and a lossless matching network, your shortened, 1 foot dipole would have a gain of only ~0.7 dB less on 160 meters than the gain of a full ...
• 18.2k
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### What is the impedance of an end-fed half-wave antenna?

It's very difficult to predict the impedance of an end-fed wire, other than to say it's high. Usually it's determined empirically. You are looking for a theoretical formulation. Consider, the ...
• 50.2k

### Impedance ratio vs. SWR

As you can see from the following equation, it is definitely not that easy. What I would do is draw a 10:1 SWR circle on a Smith Chart and assume that your tuner can match all of the infinite number ...
• 1,646
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### What exactly is impedance?

As resistance is to DC circuit analysis, impedance is to AC (or RF) circuit analysis. Now let's take a closer look at what that means, from several angles. I'm going to not include any of the math, ...
• 23.1k
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### What happens in a low loss feed-line with a high SWR

For many modulations, the modulation is very slow compared to the propagation delay of the feedline. For example, SSB is typically limited to no more than 4 kHz. That corresponds to a wavelength of of ...
• 50.2k
Accepted

• 50.2k

### How can the impedance of a half wave dipole at its resonant frequency be purely resistive when the voltage and current are seemingly not in phase?

Andrew, the typical graphics showing standing waves are showing voltage and current distribution along the wire, not phase shift from each other. Voltage and current are always in-phase at every point,...

### Why are there so many coaxial cable impedances?

Glad to see this question posted! This has a really interesting answer which I'm not qualified to write a comprehensive answer to, so here's a rather unsupported answer to help you along until someone ...
• 23.1k

### Why are there so many coaxial cable impedances?

RF Cafe cites quotes Harmon Banning of W.L. Gore & Associates, Inc.: In the early days of microwaves, around World War II, impedances were chosen depending on the application. For maximum ...
• 7,713

### What is the impedance of an off-center fed resonant dipole?

Both the real and the imaginary terms of the complex impedance across the feedpoint terminals will change as the feedpoint moves away from the electrical center of the antenna. As an example, a NEC4....
• 2,892

### Is this result correct ? [ impedance cavity based on emtamaterials using CST Microwave]

Antenna efficiency over 130% would mean a perpetual motion machine, so probably not.
• 50.2k

### Antenna tuner at the transceiver output confusion

Having a transmatch (antenna tuner) at the feed point of the antenna can be an excellent way to solve the problem of a mismatched antenna; an antenna system with the transmatch at the feed point of ...
• 8,932

### What is the difference between antenna input impedance and its radiation resistance?

No, they're separate. Radiation resistance contributes to the real part of input impedance, but so does ohmic loss (heating), and non-radiative coupling with the EM field produces the imaginary part ...
• 9,552

### How can a low-impedance load can damage a FET final amplifier?

Step away from RF for the moment, and think about the basic operation of a single-supply transistor amplifier, or even a voltage regulator. simulate this circuit – Schematic created using ...
• 23.1k