Don't assume that a good SWR means that your antenna is truly efficient and getting out there. This video goes over the other factors that weigh in on how well your antenna is operating.
Bob, THANK YOU. This is a PERFECT video for explaning this. It should be mandatory for anyone that wishes to take or sit the exam for a Ham License. Even though I myself hold the equivalent of the USA Extra Class license... I had long forgotten the importance of "R", and instead had over the years fallen into the trap of gunning for a reasonable VSWR rating. Will now look at my RigExpert & NanoVNA screens with a much better understanding. THANK YOU Bob for this excellent and to the point video.
The inductance and capacitance figures are very helpful if you want to add a matching network. As for resonance being "where the antenna is most efficient" it is often NOT the case. A feedline has least loss when terminated in it's characteristic impedance, however the entire system is more than just the feedline. I see plenty of people using quarterwave verticals fed against ground. (I am). If the ground system was perfect the feed impedance should be in the region of 35 ohms. At resonance the SWR should be about 1.4 in a 50 ohm system. In a real practical system the ground is not perfect and the impedance might be closer to 50ohms and the SWR close to 1. Sadly this makes a fairly inefficient system if a third of the power is heating up the soil. By increasing the length of the vertical the R part of the impedance rises and the antenna becomes more efficient due to a reduction in the significance of the ground loss resistance. (the pattern gets better too). Feeder loss may not increase by as much as you would guess. Great presentation of a tricky subject that needs mythbusting.
@@houseofhamradio, yes it is one of those subjects that gets more and more complex as you dive in. Related to this is the concept of the tuner at the base of the antenna. On paper it looks like a good idea but in practice it is subject to rain and spiders and I may gain a tiny fraction of a dB by choosing that path.
You lost me when you changed criteria and measurement in the middle. You started out by stating resonance is not necessarily the point where a given system is most efficient and had my rapt attention waiting for an explanation. However, you then switched to talking about SWR instead. Then you talked about changing the system, not about maximum efficiency for the system already in place. Drat, I was hoping for the next step in my enlightenment!
@@patrickbuick5459exactly. The answer is a resonant antenna designed to have a 50 ohm feed impedance with minimal ground losses, or ground efficiency. An elevated quarter wave antenna with drooped ground radials is one example. I'm not a ham.
Thanks for an excellent presentation. I see that I need to take the Smith chart screen on my NanoVNA more seriously. Another area you might take up is where on an antenna the most radiation takes place. I've heard that the high-current/low impedance portion. If that's true, then we should probably position our antennas to raise that the highest.
Great briefing, SWR is swathed in myths and legends, and people wasting hours in the impossible persuit of the legendary 1:1 ! (Helped along by coaxial losses😁)
People gravitate toward a 1:1 SWR like it's a holy grail. Things like a good ground plane or balanced counterpoise play way more into antenna performance than SWR.
@@houseofhamradio I pulled the following quote out of the ARRL Antenna Handbook Chapter 2 "Please recognize that an antenna need not be resonant in order to be an effective radiator. There is in fact nothing magic about having a resonant antenna, provided of course that you can devise some efficient means to feed the antenna. Many amateurs use non-resonant (even random-length) antennas fed with open-wire transmission lines and antenna tuners. They radiate signals just as well as those using coaxial cable and resonant antennas, and as a bonus they usually can use these antenna systems on multiple frequency bands."
A very wise ham drilled into me long ago to watch your X, or reactance, when adjusting an antenna. We often get hung up on SWR, as it is the easiest factor to understand, but it isn't the only variable in the overall system. You did a good job at explaining it.
Good job explaining, but wrong. SWR is what matters. Please study your theory before making incorrect videos. I would suggest the excellent articles by Walt Maxwell, W2DU (SK). Reactance does not absorb power. It can't. vi cos(theta) remember? How else can I say it, this video is just plain wrong. de K2XT
@@feeatlastfeeatlast5283 my dummy load has an swr of 1.0:1. there are other factors that make a good antenna besides swr. in fact many antennas have a very crappy swr but seem to work very well.
I built my first 12 Guage house wire 2m dipole. At 144 and 147 my SWR is 1.17 (nano vna). I know I need to understand inductance and capacitance better. I've been trying to understand baluns and I'm just not grasping it yet. Videos are abound on how to make them. I'd like to understand how they work, how to measure and thus how to know what I need to make.
Thanks for your comment. Baluns might be a good topic for another video but in a nutshell, Baluns (other than 1:1) help match the impedance of your antenna particularly off center fed. As your feedpoint gets away from center the impedance changes drastically and that is why we need BALUNs or usually UNUNs for end fed antennas.
Putting this comment up top even though I posted it in a reply below. The fundamentals in this video are wrong. Yes, the true meaning of resonance in an antenna is when reactance goes to zero, meaning the frequency where the reactance goes from positive to negative. The reactance has no negative effect as long as the impedance is reasonable. Walt Maxwell W2DU (SK) explains beautifully and accurately in his articles. SWR is what matters, pure and simple. The impedance actually changes along the line when the line is not perfectly matched. de K2XT
I like the Maxwell articles, like some others who have spent a lot of time and effort to try to bring clarity to a complex subject. On the other hand, I think a lot of people mis-interpret what he is saying or at least the assumptions under which it was done to be able to focus the studies. Too many variables for it to be simple, hence the massive tomes for network analysis in my electronics classes.
@@patrickbuick5459 Agree 100% Patrick! I have started going through the Maxwell articles myself to try and get up to speed on this subject. I am finding I know way less than I even realized. No matter how smart you think you are, there are always those that know more particularly in a subject as complex as this one.
@@patrickbuick5459 Walt did a fantastic job at debunking many myths. Those who can't grasp the fundamentals shouldn't be out in public spewing the myths, because gullible people are impressed by a presentation. People are swayed by a charismatic leader (or presenter on youtube) and can be made to believe ANYTHING, without evidence. Double bazooka antennas have great bandwidth, large loops are quiet, Quads open the band first, quads work fine when close to ground, a man rode to heaven on a winged horse, a man with no political experience at all can "make America great." And if reactance is tuned out of an antenna we don't have to be concerned about swr. And all that theory in books doesn't mean anything in the real world. /s (means I am being sarcastic)
@@feeatlastfeeatlast5283 That is exactly why I have been doing more and more deep diving than I intended to on various subjects to bring clarity lol. (Vertical noisier than horizontal, common mode noise versus received noise, DSP efficacy in signal readability, ground wave vs NVIS vs skip distances, antenna efficiency, power stability / voltages / voltage drop and so much more.) I'd love nothing more than access to the proper gear, including an anechoic chamber to do empirical measurements of "this vs that", as even various engineering education sources have been called into question. As an example, AGM deep cycle battery voltages as an indicator of state of charge / discharge. I got tired of charts without the conditions under which they were gathered and the general "black hole" thereabouts. Not to mention the efficicacy of chargers in recharging such beasts. So since I have the equipment, I am spending time and effort to gather empirical data to make up my own charts, which will have the conditions stated to hopefully satisfy my curiosity, answer the questions and put my mind at ease and help inform others. (I already found out that my favorite microprocessor controlled battery charger, whose manufacturer I wrote to with the question of suitability for deep cycle AGM, and whose answer was "it's good for that" to NOT fully charge that type of battery versus the one sold by the battery manufacturer. It is fantastic for starting lead acid batteries however.) Edit: Unanswered questions like... can we directly measure ground losses? What exactly do or can the R, X, L, C, Phase, RL and SWR tell me about antenna performance and what can be tweaked to get that little bit more reception? (I understand from a theoretical perspective for the most part, but translating it into being able to check into the regional 80m nets has been a bit of a bear lol.)
this is long over due for the vast majority of operators including most full call amateurs i know . Return loss which another way to look at swr is also very misunderstood . the mere sound of the word loss conjures thoughts of inefficiency . The inductive and reactive values are handy when tuning parasitic arrays i find . Simply knowing a reactive value doesn't help steer you in the right direction . Inductive values tend to mean a too long of an element or too wide of a spacing so we add capacitive reactance by moving things closer or making them shorter . the opposite can be said if the reactive value is predominantly capacitive . This theory is for when i build direct fed arrays with no matching network, that being my preferred method with antenna's of more than 4 elements . When tuning gamma matching systems the inductive or capacitive values will help make judgment on which way the gamma needs to be tuned . if its predominantly inductive you need to push the rod in further . if its predominantly capacitive pull it out . This may very well be complete bullshit but it works for me over quite a few builds now
This perhaps explains why on my wire aerials the most r.f. out does not mean the lowest SWR. For about 40 years I tuned for maximum r.f. out assuming max. r.f. out means a low SWR. Only when I built my resistive SWR meter about ten years ago I could see that tuning for max. r.f. out did not always match the lowest SWR. The difference is very tiny and hardly measurable on my r.f. pickup meter and somebody receiving my signal would not notice any difference in signal level. G4GHB
All low SWR means is that your TX is happy with a 50 ohm impedance match. Many antennas do not provide that 50 ohm load and we either use matching units or tuners to make radio happy. You are right though, max RF out to the far field and SWR are not always correlated.
Isn't 'reactance' part of the characteristic impedance? In Germany its called 'Blindwiderstand' the part of impedance that is not ohmic, i.e. the part that is coming from the AC, not DC. So imho reactance is already part of the impedance (characteristic impedance = Leitungswellenwiderstand). The coax-cable and the connections together have to match the characteristic impedance of the radio antenna output. Its all about reactance (or char. impedance to be precise).
That is certainly a more accurate although more difficult for many to understand. I tried to dumb it down just enough but may have missed some of the nuance in doing so. Thanks for providing the extra info.
Absolutely! that is "Resonance" and means your antenna should transmit the most power to the air. At least in theory. Reality sometimes gets in the way and it doesn't include radiation patterns which also impact how well the other end hears you.
@@timdbl7804 I am basing that on my electronics knowledge. An antenna is essentially a filter and filters transfer the most power at resonance. One important point about antennas though is there is a lot more happening that can change things. Location, height, ground quality can all impact how well a signal reaches the far end.
Z is the complex impedance as where R is the pure resistive part and X is the reactance part. I may try and do a video on those later or maybe leave that to the RF engineers to try and explain :) I was trying to keep the discussion to what hams really need to know.
I've always out of instinct thought the 52 ohm load should come from the antenna and NOT the matching gadgets we use to fake our systems out into believing the load is correct. So many hams warming up their labs with match boxes these days and hes we forget about those roasting base loads, another cheat.
Don't completely dismiss matching units. There are many very efficient antennas that have matching units. One of my favorite portable antennas is an end fed half wave that has a 49:1 matching transformer and it works wonders with 5 watts. It isn't cheating if it gets you on the air. You do need to understand what your configuration is and what compromises you may be introducing.
You are confusing the terms impedance and resistance. Impedance, denoted by Z, is a complex figure, with resistance, R, being its real component, and reactance, X, the imaginary component.
Good point from an engineer perspective and I certainly don't disagree. In general terms for the average ham. (remember that this is a ham radio channel) we speak of impedance as resistance to RF in ohms or in even simpler terms, is my antenna system presenting a 50 ohm load to the transmitter? In trying to take these complex concepts and boil it down to the operator's perspective, we often lose clarity. Thanks for the additional info for viewers to see.
That is not the true definition of resonance, more a resultant. I'm a CBer and am shocked that most hams believe this because that is what they are taught. Resonance is the wavelength fitting the electrical length of the radiating element. That is about the simplest definition of resonance.
Thanks for your comment. Many folks (ham an otherwise) believe that a 1:1 SWR is resonance, actually resonance is where inductive and capacitive reactance are equal and cancel each other out. This does not equate to a 1:1 SWR as that is having the purely resistive part being 50 ohms.
@@houseofhamradio yeah, that's right. Another common misconception. I actually love how these American CBers with their crude amplifiers (varying input and output impedances) believe in the patch lead length thing. They don't understand coaxial transformation.
