19 votes

What is a Gamma match in the context of the driven element of a Yagi antenna?

Clearly capacitance is the key Capacitance is just one part of it. The gamma match in your question is three things: A sort of folded dipole, performing an impedance step-up A parallel shorted ...
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17 votes
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How did hams manage to tune their antennas before VSWR meters?

Mostly, they used RF Ammeters in series with the antenna. The first ones were hot-wire ammeters which were completely mechanical devices. One end of a thin nichrome wire (or other wire of sufficiently ...
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  • 7,495
14 votes
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What is a Gamma match in the context of the driven element of a Yagi antenna?

A gamma-match serves a triple purpose: As a small diameter wire parallel and in close vicinity with the main radiating element, it will carry only a fraction of the main element current while being ...
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  • 1,267
10 votes
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RF signal level when the antenna is disconnected

The situations described, schematically: simulate this circuit – Schematic created using CircuitLab When the source and load are matched (Rantenna = Rreceiver), you will be measuring the ...
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10 votes

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 ...
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10 votes
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Why aren't "ghosts" and intersymbol interference due to unmatched impedance (high SWR) a concern for HF receivers?

Intersymbol Interference (ISI) — or analog equivalents, like ghosting — are relevant only when the difference in time of arrival between the primary and reflected signal are significant compared to ...
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9 votes
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How to combine two 50 Ω antennas such that they appear as one 50 Ω load?

The canonical solution to this problem is a Wilkinson power divider. There are of course other power dividers, but the Wilkinson is easy to fabricate, provides good isolation between the output ports, ...
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9 votes
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Do I need a separate SWR meter if the transceiver has one built-in?

You'll be fine to start without an additional SWR meter. An SWR meter doesn't provide any protection. With or without an SWR meter, you'd want to start on a new antenna on low power, then increase ...
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8 votes
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Tuning/trimming a ground plane antenna

My trick is instead of cutting, rather extend the whip first, and see if the SWR gets better or worse. Extend it 1/2" with a bit of wire wrapped around it and sticking out. If the SWR gets better, ...
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  • 7,817
8 votes

RigExpert AA-35 - Interpreting The Information

First, a general statement: the antenna analyzer has one set parameter, the frequency, and one measured parameter, the impedance (which is a complex number and therefore requires two real numbers to ...
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  • 22.9k
8 votes
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Do you need to analyse the SWR of your radio repeatedly? Or periodically? If so, Why?

If nothing about the physical situation changes, then the SWR will not change. But something might change in the long run, perhaps: Damage to the feed line (water intrusion, sun damage to insulation, ...
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7 votes
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How do I set up my radio for an antenna tuner?

Your TS430S has a solid state final and no internal antenna tuner. As such it is designed to work into a 50 ohm load at all times. This means you can disregard this note in your antenna tuner manual. ...
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  • 18.1k
7 votes

Coax cable as antenna for 5 watt handy

The electrically shortened antennas often found on HTs are not simple pieces of wire, but coils: By Shootthedevgru at English Wikipedia, CC BY-SA 3.0 The coil adds inductance over the length of the ...
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7 votes
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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?

The SWR is related to the reflection coefficient $\Gamma$: $$ \Gamma = {Z_L - Z_0 \over Z_L + Z_0 } $$ $$ \text{VSWR} = {1+|\Gamma| \over 1 - |\Gamma|} $$ where: $Z_0$ is the feedline impedance, ...
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7 votes
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Trying to understand the work of 4:1 coax balun

Think of it first without the feedline: The half-wavelength of transmission line provides a 180 degree phase shift, and the (short) connection between the shield ends is "ground". That means it's at ...
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7 votes
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Can I use a directional coupler to block reflected AC current from a mismatched antenna?

There is a device that does this, but it's not a directional coupler. Rather, it's a circulator. A directional coupler isn't suitable since the forward and reflected ports merely "sample" the power ...
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7 votes

What is antenna reactance?

Reactance is the imaginary part of impedance. Together with the real part, resistance, impedance describes how a given load will respond to an AC voltage or current source. While for DC analysis ...
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7 votes

Are "end-fed" antennas really more multi-band than dipoles?

It's mostly real. To a first approximation, a center-fed dipole will have a reasonable impedance on bands where it is an odd multiple of a half wavelength (the fundamental, third harmonic, fifth ...
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  • 8,833
6 votes
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Does Coax Limit the Maximum SWR a Transmitter 'Sees'?

The source of the SWR limit on the transmitter end is the losses in the feedline. In general, the higher the matched line loss, the lower the maximum SWR that will be present at the transmitter end. ...
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6 votes
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Removing the whip on a 2m/70cm antenna makes no difference

If the SWR was very poor with the whip installed, you could simply be hitting the limits of your analyzer. Inexpensive analyzers are not very precise when the load is very poorly matched. Alternately,...
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6 votes

Impedance matching: Why do components behave totally differently from theory?

Firstly, at 900+ MHz, shorting out components to take antenna impedance measurements is not a good practice as the lead length can be a substantial portion of a wavelength. Stray inductance and ...
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  • 18.1k
6 votes

Impedance Matching between RF Amplifier Stages

There is no need to "pin" an interstage impedance. You may directly transform from the native output impedance of one stage to the native input impedance of the next without going through an ...
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  • 18.1k
6 votes
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Better SWR bandwidth

A low SWR bandwidth is a consequence of shortening the antenna for mobile use. SWR bandwidth is related to the antenna system's Q factor, the ratio of energy stored to energy dissipated per cycle. A ...
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6 votes

How to match low impedance of NVIS Dipole?

Many baluns will work just fine in either direction, though there isn't just one kind of "4:1 balun". This kind is wound on two cores, and works as a common-mode choke: simulate this circuit – ...
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6 votes
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Estimating SWR based on multiples of resonant length

Very high. Harmonics work the other way around — antennas can be useful on higher bands than the design band, but almost never lower bands. A dipole cut for 40m might be good on 15m. An end-fed or a ...
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  • 8,833
6 votes
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Is testing SWR *practically* less important for 2m/70cm than HF bands?

I would say in practice it is less important because hams use different types of antennas for HF and for VUHF. At HF, the same antenna is often used for many bands. The bands have large fractional ...
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  • 7,817
6 votes
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Impedance miss-match short vs long section?

Hams usually send just one frequency down a transmission line (as opposed to say high speed data like HDMI). So it's much simpler to analyse impedance down the line, than look at the reflections. ...
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  • 7,817
6 votes

Reasons for an antenna tuner at the transmitter other than transmitter protection?

Just because the finals don't go up in smoke when driving a mismatched load, doesn't mean they're working well. They will probably deliver less power to the antenna than they would in a matched ...
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  • 8,833
6 votes

Are "end-fed" antennas really more multi-band than dipoles?

End fed antennas do work on more bands than centre fed dipoles. The reason is that end fed antennas are resonant on all harmonics, while normal dipoles only resonate on every other harmonic. To see ...
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  • 305
5 votes

Intermittent High SWR

The MA5B is rated for 1,200 watts PEP. 200 watts is certainly well below that threshold. Things to check: Arcing, corrosion or moisture inside the match box A loose or corroded connection from the ...
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  • 18.1k

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