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 ...


11

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 ...


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

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 ...


9

There are a lot of topics in this question, so let's take them one at a time. I figure the transmitter has a 50-ohm pure resistive output Not necessarily. You're probably arriving at this conclusion based on the maximum power transfer theorem. Which of these circuits delivers more power to the load resistor? simulate this circuit – Schematic created ...


8

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(...


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 ...


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

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 ...


5

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 loop for 40m might be good on 20m and 10m. But pretty much any design of 40m antenna is going to be a half-size antenna on 80m, and very unlikely to be tunable ...


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

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

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

So, yes, to tune a resonant antenna, you'll need an adjustable capacitor or inductor. You'd usually go the capacitor route, since adjustable caps are smaller, cheaper, and more exact, usually. Bonus: There's electronically variable capacitors! They're called varactors or varicaps (or just variable capacitance diode), and they're a very mature (read: old &...


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

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 ...


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 ...


4

It is not normal to have and use tuners on both ends of a feed line. The purpose of an antenna tuner is to provide an adjustable impedance transformation. The reason we want that transformation is so that the transmitter can work into the (usually) 50 Ω load it was designed for. If you have an antenna tuner located (only) at the antenna, then this is the ...


4

Let's say the antenna impedance on a given frequency is 100 Ohm, the feedline is lossless 50 Ohm, the transceiver input impedance is 50 Ohm. Between the antenna feed point and the feedline SWR = 2, 11% reflected power. This is a bit of dangerous thinking, because the distance between the antenna feedpoint and the feedline is zero. As such there can be no ...


4

SWR swings wildly, like a loose connection (there are no loose connections) SWR should not change in a properly operating system (though SWR meters may show changing SWR when the transmit power changes, so check with a mode other than SSB to be sure). Are you sure that there's no loose connections? You've checked all the connections that you made, but what ...


4

If it acts like a loose connection, it probably is one, just not an obvious one. If it fluctuates from day to day, especially with a pattern, it could be water intrusion. If it works worse on hot days, maybe the water is actually helping -- maybe you have wire fatigue, and the water is bridging the gap. Similarly, if the SWR goes up (or down) as you first ...


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