What is an Antenna Tuner and what does it do for me? (038) 

Ya know ... I was thinking about the tuner as the "black box" and the conservation of matter and energy. Now ... as that reflected energy from the feedline enters the tuner it meets another impedance change within the components of the tuner itself and some portion of that reflected energy gets sent back to the output from whence it came. We are still left with energy that isn't reflected and it has to go somewhere. So, while pure, ideal inductors and capacitors do not have the means to dissipate energy in heat, real world ones do as does the various wires that make up the tuner, making connections from place to place, not to mention the contact resistance of connectors and switches. As far as SWR diminishing...let's think a bit about that. I send out a pulse of 100 watts to an antenna through a lossy feedline (0.46 dB). 90 watts gets to the antenna which reflects back 9 watts at the transmitter (~2:1 SWR). By the time it gets back to the transmitter it is now 8.1 watts. ... let's just say for giggles that we get the same 10% of the power being reflected back from the transmitter. This means that 90% of this 8.1 watts hits the transmitter and 0.81 watts heads back to the antenna. It is now 0.729 watts by the time it gets to the antenna. Each trip power is lost in the feedline and only a percentage of the power is reflected. Meanwhile, the transmitter is still pumping out power, which adds to all of this. So, SWR never diminishes. It is a constant. Reflected power will always be present in the feedline without diminishing. Yes, with this trip back and forth between the transmitter and the antenna, the reflected power (not the SWR) rattling about in the feedline and being attenuated at every pass by the feedline does "dribble out" the antenna end. I did a study with this very scenario, running back and forth with feedline loss and reflected power and all. We really cannot count on much beyond the initial power that makes it past the first reflection. We do get a little more, but absolutely not enough to think it is doing anything for us.

@@eie_for_you if the feedline was theoretically lossless how much of the reflected power gets radiated by the antenna

Thanks! 🙂

We are on the same page, my friend! 🙂

I think you are taking me wrongly, here. When I talk about an antenna being "resonant" I refer to the condition where the antenna is physically resonant at the desired frequency, such as with a dipole where each leg is electrically 1/4 wavelength long. Nothing that we do in the shack can change the physics of the antenna itself. We can match impedances so as to deliver as much power to the antenna as possible, but the physical wire antenna itself remains unchanged. The use of a matching network (AKA: Antenna Tuner) brings the entire system together so "everyone" is quite happy and we are exporting as much power as possible. Yes, as a system (including the feedline and antenna) is, indeed, now resonant. But to say that the physical nature of the antenna has been made resonant is still a misnomer regardless of who says it....from my perspective. 🙂

I am noodling on all of this...ya got me thinking some more about this.🙂

Thanks! 🙂

You are very welcome! 🙂

You are welcome! Yeah, it is amazing the misunderstandings that exist simply because of the choice of nomenclature used. My old Drake MN-2000 says "Matching Network" on the front because that is what it does (and ALL other "antenna tuners"). All we can do is try to educate and hope some of it sticks. 🙂

You are right, the "plate and load" adjustment are a matching network of themselves. The difference is what they are actually matching in terms of impedances. The output impedance of the final amplifier is not naturally 50 Ohms or even close to it. It's output impedance is approximately the same as the plate load. At resonance, this is pretty high which is why we dip the place current. The purpose of the plate and load adjustments is designed to translate the high output impedance of the finals to a 50 Ohm environment. It has been a very, very long time since I owned a rig with plate and load adjustments to be made. If it were me ... I'd set them in the "starting position" as dictated by the radio's manual first. Then dip the plate. Now adjust the antenna tuner for best SWR. I would then go back and adjust the plate and load as per the radio's manual. And finally, I'd give the antenna tuner its last adjustment. 🙂

You are welcome, dear brother!

Unless the antenna tuner presents a perfect short or a perfect open to the coax, some percentage of the reflected power from the antenna does, by definition, end up passing into the antenna tuner. This power has to go somewhere. It doesn’t end up at the transmitter, so it has to be dissipated in heat in the antenna tuner. I also have a hard time believing that it would be going back in phase with the forward power because the phasing would depend entirely on the electrical length of the coax.

​@@eie_for_you the tuner would get hot wouldn't it with the heat, yet it doesn't?

This is what I'm trying to find out, because opinions differ. I don't have an ATU at the moment, but from what I understand, the ATU never gets warm, which it would if it were dissipating energy (it's probably dissipating some, but maybe only like 5% of the reflected energy). From what I keep hearing, it re-reflects the signal back to the antenna. In this explanation, the losses happen in the transmission line (coax) between the tuner and the antenna as a percentage of the signal bounces back and forth repeatedly until it is finally radiated or lost to heat. So what I'm trying to figure out is - would an antenna connected straight to the tuner be highly efficient, as the part of the signal being reflected keeps getting re-reflected straight back into the antenna without going through any feedline. In this setup, the tuner would be out at the antenna feed point (weather proofing would be necessary) and the transmission line (coax) would run back inside to your radio. Does this make sense?

​@@eie_for_youisn't that what a conjugate match does?

Thanks!

An antenna tuner is composed of both an inductor and, very often, two capacitors in a pi configuration. So, it is noticeably more than just a base loading coil. While I have not studied these things in detail, as I understand it, the coil used as the base coil loading for an antenna is not part of the radiator. It is just a means of making the antenna "look" longer than it really is. So, I suppose you could do what you say, but, like the base loading coil, the tuner would not be a radiating element. My guess ... I guess.

@@eie_for_you Some people say the complete opposite (see palomar engineers’ article on “non-resonant-vs-resonant-antennas”). I can’t paste the link as RU-vid keeps deleting my post. Who is right then? You make a strong statement @11:57 “an antenna tuner is not actually an antenna tuner…it does absolutely nothing to tune your antenna if your antenna is not tuned to the frequency that you're attempting to use…it’s radiation efficiency is not going to improve….”

@@02vLxcZF The radiation efficiency of an antenna is determined by its physical structure and installation environment. Nothing done at the transmitter end of a feedline changes this physical reality. We can pump more energy at it through impedance matching and making the transmitter happier through the use of an antenna matching network. This gives the "appearance" of improved antenna performance, but it does nothing to change the physical realities of the antenna itself. You could do some virtual experiments in 4NEC2 antenna modeling program which will report antenna radiation efficiency and see this for yourself.

@@02vLxcZF I have found the article you refer to ... I will take a look at it.

@@eie_for_you Thanks, this stuff is driving me crazy, unless both parties are right. My simplistic understanding is that as @BShocked was implying, the antenna tuner modifies the electrical length of the antenna in a similar way that a coil would at its base, and hence its radiation properties are modified (e.g. resonance frequency). Would be most interested to hear your thoughts

Yes, the "antenna tuner" does, indeed make the transmitter see a nice impedance that it want to see so that it is very happy to output all the power it has to the antenna. As an electrical engineer who not only studied the theory, but lived it as a professional engineer for many years, I can assure you, the "antenna tuner" does not tune the antenna. It is an impedance matching device. It makes it so the transmitter sees the impedance it wants to see and the end of the coax sees what it wants to see. The feedline is, say, a 50 Ohm feedline. The antenna is exhibiting an impedance of maybe 100+150j. NOTHING I do at the other end of the feedline is going to change the physical characteristics of the antenna to change this to be 50+0j and resonant at the intended frequency. The antenna is what it is. The fact that there is an impedance mismatch between the feedline and the antenna causes reflected waves. This is the basis of Time Domain Reflectometry (TDR). If I have a piece of 50 Ohm coax mated to a 75 Ohm coax, when I send a pulse down that coax I will see a return pulse indicating the mismatched impedances right there where they meet. This is how they find the location of damage to a piece of feedline. In the past what we now often call an "antenna tuner" was called a "matching network" or a "transmatch" which properly identifies what the device is doing. Unfortunately, somewhere along the way someone started calling it an "antenna tuner" and the term stuck. This inaccurate terminology has led a LOT of people to believe that it actually tunes the antenna. Well, it does not and cannot accomplish this task.🙂

Nice topic...Trying to understand how a ham shack Located antenna Tuner actually Protects an older traditional 50 ohm Transmitter/transceiver or rf power Amplifier without swr Foldback protection feature from coax fed high Swr antenna tuning Mismatch..Clearly the "L" o r "T" antenna tuner will let Rf Final stage device "See" a good Low Swr & power-up full power....Typical antenna tuners are Bi-Directional matching devices & should permit any Reflected matched complex Z antenna power to simply "Pass thru" the tuner & reach the Rf final stage causing over-load, overheating Final damage....Modern high Q, efficient antenna Tuners have very little rf loss Either direction & Dissipate little heating....Usually only coaxial Rf Isolators & Circulators guarantee 1 way Directional power Continuity.....So how does the typical antenna tuner protect the rf Final stage from antenna Reflected power ??

@@tomstrum6259 Wow! Now THAT is a good question! The difference between the receive signal coming down the coax to the antenna tuner and the reflected power coming down the coax to the antenna tuner is that the reflected power is meeting the incident power coming from the transmitter through the tuner toward the antenna. We all know that the incident signal is phase shifted as it is going through the tuner in addition to the impedance matching. We can kind of picturing this something like waves on a pond. We initiate a wave from the shore which reflects off of an object just off the shore. If a person on the short initiates just the right wave going away from the shore, the right phase and amplitude, then the wave coming toward the shore will not reach the shore at all. In fact, it might even be reflected back away from the shore. I think this same sort of phenomenon is occurring on the feedline side of the antenna tuner only in terms of the phase and amplitude of the incident R.F.. 🙂

I do understand that. Too many folks think that it does something it does not just because of the common name of it. Yet, I wanted to lay down the case first so that this correction in terminology was backed up by real "data" and did not just appear to be my opinion. This is why I kept that correction to the end.

​​​@@eie_for_youdoes it tune out the reactance of the system?

@@paulm0hpd319 It matches the complex impedance as seen at the end of the coax to the complex output impedance as seen at the output of the transmitter. So, it does not necessarily remove all reactance as much as it makes what the transmitter sees to be what it wants to see. Is it a perfect, nonreactive impedance? Not necessarily because the output impedance of the transmitter, itself, is not necessarily completely devoid of reactive components. 🙂

@@eie_for_you nothing is absolutely perfect but the general conception is that the tuner tunes out the reactance with a conjugate match therefore deeming the system resonant

@@paulm0hpd319 General conceptions are not necessarily technically correct, either. Its job is impedance transformation.