We’re rewarding the question askers & reputations are being recalculated! Read more.

# Tag Info

13

There are two different parts to antenna tuning: transmission line impedance matching and resonance. The antenna is at resonance when it presents a purely resistive load to the transmitter. That is, the reactive component of the load is 0: there exists no inductance or capacitance in the load. However, resonance says nothing about the value of the ...

10

An antenna matching network (aka "tuner") does not affect the conditions of the load (antenna) or the transmission line between the load and the matching network. The matching network transforms the impedance "looking into" the transmission line to a more desirable value, typically 50$\Omega$ for ham applications. If the network manages to achieve such a "...

9

And if it is possible to use a tuner to make a transmitter feed power into a coat hanger then why do we worry about making resonant antennas in the first place? In a word - efficiency. Consider that a full size 40 meter, 1/2 wavelength dipole is approximately 65 feet (19.8 meters) long. A dipole that is only 2 feet (0.6 meters) long, would have a gain of ...

7

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. If the tuner was used with a radio with tube finals then you would need to heed this cautionary note. If the tuner is used with a radio that has a built in ...

7

I am pretty sure this isn't covered explicitly in Part 97 and probably falls under the "don't cause intentional interference" clause. The practice I was taught is this: Tune off the pileup you found several KHz to a 'clear' spot reduce power to the either the lowest the rig will go or the least that will facilitate the tuning process Switch to CW mode ...

7

How can I transmit without an antenna tuner? Simple. You use an antenna that's already tuned. There are plenty of radios that operate without any tuner. For example, basically every VHF radio. One reason for this is that most VHF antennas are purchased rather than manufactured by the amateur, and the antenna manufacturer has already tested and tuned the ...

6

The SWR meter helps you match the impedance of the radio to the antenna. If the impedance is mismatched, you lose power. If the impedance mismatch is large, you risk damaging your radio, particularly on the lower frequencies. Tube based transmitters and amplifiers have more leeway for mismatch than semiconductor based amplifiers. Lower power transmitters ...

6

My understanding is that they can neutralize the imbalance between inductive and capacitive reactance so the transceiver can couple the most power out (or in) even though an antenna might not be resonant on a particular operating frequency, since overall impedance (Z) consists of three parts, two of which are reactance dependent on frequency: X(sub)L and X(...

6

Any material with a relative permeability greater than 1 will increase inductance when inserted into a coil. Note that permeability is a complex number and frequency dependent. The imaginary part of permeability contributes to loss and appears as a resistance, so the addition of some material in the coil may increase inductance and also add resistance. ...

5

Your transmitter has something called an "output impedance" and expects to be loaded with this impedance. The standard is 50 ohms. You don't need to look up the output impedance, it was standardized and anything made in the last 50 years will expect 50 ohms. The 50 ohms the tranmitter expects is measured at RF frequencies. Many antennas look like short ...

5

Most radios with SWR protection don't detect SWR, they just detect reflected power. It's a much simpler (read that as cheaper) circuit to implement and it's what really matters anyway. The manufacturer will have established a threshold for reflected power, based on the MOSFET's tolerance. If the circuit sees more than this it will either clamp it at the ...

5

The original Yaesu FT-101 tuning instructions state the following: Do not use antennas which are untuned or exhibit an SWR of more than 2:1. An external antenna tuner can usually work with a much broader mismatch range. If you have a "random wire" or otherwise untuned antenna, a tuner is clearly required. A slight mismatch (2:1 or less) can be handled by ...

5

Q isn't related to the voltage. A simple definition of Q could be the ratio of the total energy in a system to the energy lost per cycle. So the biggest factor in Q is the loss in the dielectric. In general, vacuum variable capacitors (VVC) have a higher Q than air variable capacitors (AVC) but there is some overlap. A common range for VVCs is a Q of ...

5

A simple tuner might be just a capacitor and an inductor: simulate this circuit – Schematic created using CircuitLab For more flexibility, many tuners add a 2nd capacitor to make a pi network: simulate this circuit If you were to have two such tuners: simulate this circuit Well, now you just have more elements which can be adjusted. There's ...

5

The benefit of placing a tuner at the antenna (rather than at the transmitter) in any circumstance is a reduction in the SWR on the coax. This results in a reduction of losses. There's a bit of myth that a bad SWR causes common mode current (radiating coax), but this isn't the whole picture. At the feedpoint, current is divided between the common and ...

5

I suggest you feed it in the center with open-wire (ladder) line and a balanced antenna tuner. (I have done that for many years). With the right tuner, you can obtain a near-perfect match anywhere on those bands. Also, feeding it in the center eliminates the need for a good RF ground or radial system, as opposed to end-feeding it. Glenn, W9IQ has a ...

4

Another phenomenon that might play into the impression that HF transmitters are more susceptible to damage from high VSWR is feedline loss. Feedline loss increases as frequency increases. So at HF frequencies the power reaching the antenna feedpoint is higher due to lower feedline losses, and for the same reason the signal reflected back from the antenna ...

4

You can tune by receiving, generally. When your antenna is tuned, then SWR losses are minimized. By reciprocity this minimizes receive losses also, so you can just listen to noise and tune for maximum received noise level. In fact, with more complicated tuners that have more adjustments, this is usually the first step so that you can be in the right ballpark ...

4

There are many problems here, only one of which has to do with impedance: Your antenna is (I assume) horizontally polarized whereas most VHF signals you might scan for (particularly ones where one end of the normal link is mobile, e.g. a car) are vertically polarized. Your antenna will have a highly irregular pattern, with many nulls (directions in which ...

4

Yes, you'll need an external tuner, unless your antenna is already matched sufficiently well to 50 ohms. The objective of the tuner is to transform the impedance seen by some signal source, like your radio, or the amplifier. The amplifier will already be designed to have a 50 ohm input. Your radio, transmitting into that, is designed for a 50 ohm output, so ...

4

First, consider how the circuit works. It's a Wheatstone bridge, although you might have to squint and turn your head to see it. Think about how "Tune" is a connection to ground through what should be a 50 ohm impedance. Here it is redrawn a bit: simulate this circuit – Schematic created using CircuitLab When the antenna is tuned, then R2 and R3 make ...

4

This can indeed be a fine setup. With a suitably low-loss feedline, and a good tuner, just about anything can be made to function as an effective antenna. There are two factors that determine the losses in this situation: the matched loss of the feedline, a function of length and the attenuation specified in the datasheet, and the operating SWR on the ...

4

I made a NEC model of an antenna with the dimensions of your "long wire" on 14.2MHz, found the values of C1, L1 and C2 that produce a 50$\Omega$ match and simulated the network to observe the voltages across the capacitors with 100W dissipated in the load. The voltage across C1 was 220VRMS, over 300V peak. Given all the variables that I did not evaluate, ...

4

TL;DR: It's NOT mild steel, brass, or aluminum. I connected two different inductors to an antenna analyzer, and all of the above materials decreased the inductance as they were inserted. The larger the diameter of the steel I inserted, the lower the inductance and the greater the loss. It was the worst material I tried. When I inserted some powdered iron ...

3

You say your dipole's total length is 20 meters, and you are using it on the 20 meter band. When the dipole's length is equal to some multiple of the wavelength (1λ, 2λ, 3λ, ...) the dipole is antiresonant, and the feedpoint impedance is at a maximum. Being the worst possible match, it will require maximum range from your tuner. If the total length of the ...

3

The overall antenna length being very close to a perfect 1 wavelength is the linchpin of the issue, I suspect. It is not surprising that it can be easily moved outside of the tuning capability of your tuner, as the impedance peak near resonance can be quite sharp (depending on the Q of the antenna system), allowing the impedance to change by hundreds or even ...

3

Reduce Power One of the bad effects of SWR is heating of the power amplifier inside the radio. This heating occurs because of reflected power. The higher the SWR, the less power is transmitted out the antenna and more of the power is reflected back to the radio to become heat. You can reduce reflected power by reducing output power. For instance, ...

3

Two tuners in series might "work" but you should consider all of the factors at play. Since you cannot match the antenna with a single tuner, this indicates a fairly high SWR on the line. This will cause not only higher feedline losses but could lead to the development of sufficient voltage or current on the feedline to cause its failure. This is ...

3

An end fed, 1/2 wavelength antenna will have a relatively high impedance of 5k ohms or more. So a 9:1, or greater, ratio of balun may reduce the impedance sufficiently to help your tuner get a match and help avoid a voltage flash-over in your tuner. However, there is another issue that may require some planning. When using an end fed antenna, the current on ...

3

Inspection of figures 17.17 through 17.19 in the ARRL Handbook suggest that the components in your Pi network might need to be adjusted: Jim Tonne, W4ENE, wrote a utility called PIEL to calculate output tank values. A Pi-L network - a Pi network with an L-network extension - is frequently used to match a wider range of impedances than a Pi network alone can ...

Only top voted, non community-wiki answers of a minimum length are eligible
{"extraction_info": {"found_math": true, "script_math_tex": 0, "script_math_asciimath": 0, "math_annotations": 0, "math_alttext": 0, "mathml": 0, "mathjax_tag": 0, "mathjax_inline_tex": 1, "mathjax_display_tex": 0, "mathjax_asciimath": 0, "img_math": 0, "codecogs_latex": 0, "wp_latex": 0, "mimetex.cgi": 0, "/images/math/codecogs": 0, "mathtex.cgi": 0, "katex": 0, "math-container": 0, "wp-katex-eq": 0, "align": 0, "equation": 0, "x-ck12": 0, "texerror": 0, "math_score": 0.7154213190078735, "perplexity": 1517.493915114219}, "config": {"markdown_headings": true, "markdown_code": true, "boilerplate_config": {"ratio_threshold": 0.18, "absolute_threshold": 10, "end_threshold": 15, "enable": true}, "remove_buttons": true, "remove_image_figures": true, "remove_link_clusters": true, "table_config": {"min_rows": 2, "min_cols": 3, "format": "plain"}, "remove_chinese": true, "remove_edit_buttons": true, "extract_latex": true}, "warc_path": "s3://commoncrawl/crawl-data/CC-MAIN-2019-47/segments/1573496669813.71/warc/CC-MAIN-20191118182116-20191118210116-00131.warc.gz"}