HAM RADIO SWR & ANTENNA TUNERS
Baluns and Unun Loss
SWR & Tuners & Baluns...(kind of like "Lions & Tigers & Bears").... What does it all mean? Well lets take them step by step. As I mentioned on the home page, I am not going to throw pages and pages of techno-jargon at you, I am going to try to keep it simple. Reading Ham Radio pages shouldn't feel like its a test. I just want to try to impart useful information if I can and be helpful. Unlike some other deplorable websites, I am not here to try to convince you that I know more then anyone else. I most certainly don't. But I know enough to be dangerous. So here's the skinny:
SWR: Standing Wave Ratio....... This basically is a measurement of the amount of forward RF power that gets from your radio to the antenna versus the amount that gets reflected back towards your radio. Under perfect conditions with an SWR of 1.0 to 1 all of the RF traveling down the transmission line gets to the antenna and gets radiated into space. The picture above represents perfect SWR. This only occurs when the load (antenna) has an impedance identical to that of the transmission line. It also must have no Reactance ( Inductance and Capacitance, but we're not going there, so don't fret). When the Line Impedance and the Load Impedance are identical you have a 1.0 - 1 SWR perfecto ! No Antenna Tuner Needed.
When the impedance of the load (antenna in our case) is not equal to the line impedance, the antenna cannot absorb 100% of the RF sent down the transmission line, and some of it gets reflected back down the transmission line towards the radio. This is called reflected power. The higher the ratio of reflected power to forward power the higher the SWR. The picture below represents some reflected power or some SWR. This reflected power is partly lost power that never gets to the antenna. It travels back down the coax (heating it up very slightly) , and can cause other more annoying problems like; some of the reflected power hits the output transistors in your radio and heats them up as well. As you might have guessed hot transistors is a no - no for radio longevity. Most of it will get reflected back towards the antenna, reaching it and then getting reflected back again creating and endless loop until it has been dissipated by heat . It also can radiate just like the forward RF that gets out through your antenna, except it uses your transmission line or coax as a radiator. This creates RFI and interference to other electronic devices in your house and other homes near you. Since your coax is now competing with your antenna if only by a small amount, your antenna pattern will now get screwed up, by the extra RF radiating from the coax, heading in unknown directions. This is starting to sound bad isn't it?
Its not all that bad usually. Whats the point that you should get worried? I would say if your SWR is above 2.5 - 1 you might want to consider doing something about it. Most times your radio or amplifier will already being doing something about it, by automatically lowering your power, as to not fry those pesky output transistors. But you shouldn't rely on that to cure the problem. because your still losing power and probably creating interference somewhere.
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So how do you fix this? Well the best way is to take your antenna down and resize it until you get a reasonable SWR...like below 1.5 somewhere. But since most people are lazy they will opt for an easier way to fix the problem. Enter the
Antenna Tuner
Antenna Tuners
If there ever was a wrong name applied to a ham radio piece of equipment its the Antenna Tuner. Does this tune your Antenna? No The only way to tune your antenna is to take it down and resize it period. So why is it called a Antenna Tuner. I have a feeling some less then honest manufacturers brought out the name and it stuck. It sounds like it solves the problem doesn't it? And it can sit in your shack next to the other equipment you have ! You don't have to go near that antenna on your roof, on your tower, or in your tree. It really should be called an Impedance Matcher, but there's that confusing word "Impedance" again, so manufacturers probably thought Antenna Tuner sounded better. Anyway so what does it do? Well in reality it tries to trick your radio or amplifier into thinking everything is perfect. Meaning the Antenna system has the same impedance (usually 50 ohms) as the radio antenna output (so239). That way the radio or amplifier can not worry and send full power down the transmission line. Antenna tuners do not change the impedance of your antenna and in fact do not TUNE the antenna at all.
If you have an automatic tuner, you press a button that says "tune" what could be easier? If you have a manual tuner you have to play with 2 knobs one called "tune" the other called "load" or other names . You look at the SWR meter on the tuner while transmitting and hopefully you can get SWR down to near 1 to 1 to look good to your radio or amplifier, so it has no excuse for not giving you full power output. You should always use low power when using a tuner first, before you blast it with 1.5KW if your so inclined. Proper tuning instructions below.
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How to use a Tuner properly:
As stated above most tuners have two big knobs, they will be called " Transmitter and Antenna" or " Tune and Load " or "Capacitance and Inductance" or "Input and Output", "Bert and Ernie" or whatever. In any case the TWO BIG KNOBS is what you want.
Before playing with your knobs, look at the other switch or Roller Inductor (the one with a rolling scale). Most tuners have either a rotary switch which allows you to select the band you plan to transmit on, or a "Roller Inductor" (better choice).
BEGIN : Go to the frequency you want to transmit on lets say 14.200 mhz. (or an unused frequency near it) LISTEN TO NOISE. While listening to the noise , turn the Roller Inductor ONLY until you hear the highest level of noise on this frequency. Or the highest "S" meter reading. Stop leave it there. This is more precise then the OEM rotary switch where you pick a band. But if you have that, just set it to 20 meters or 14 mhz. If you have a switch NEVER turn it while transmitting Period.
NEXT: Using 20-50 watts (preferably in FM mode) key your microphone and hold it down. Turn the first big knob until you get the highest RF output reading on the scale of the tuner, then turn the second knob until you get the same result; the highest RF output or lowest SWR reading (they are the inverse of one another). Usually the knobs move towards the higher end of their 1 - 100 scales, indicating high efficiency for the tuner. Tuners have loss as previously explained. Stop leave them there.
NEXT (2): Now move the Roller Inductor ever so slightly (if you have one) until you get the SWR down as low as possible. If you wish you can continue to play with your Big Knobs gently and slowly to get the same low SWR result. Stop, you are good to go.
FINAL COUNTDOWN: Do this for every antenna change and frequency change, whenever you are on the air. And certainly BEFORE you key up any amplifier. OR: You could just make sure your antenna is cut to the right length, and not worry about a tuner. NEVER try to tune a wire antenna for a band it was not meant for. Like tuning your 20 foot wire for 160 meters.
If you just set the manufacturers Roller Inductor settings to the manual suggestions, you may be losing power through the tuner. LISTEN for the loudest noise on the Roller Inductor , then start tuning. Above all don't be a LID, read the instructions carefully, they may differ slightly from the above. You cannot blame everything on MFJ! If its a tuner that blew up.....YOU most likely blew it up.
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Tuners are composed of reactive components, this means they react only to the frequency applied to them. So if you change frequency, you will have to "re-tune" your Tuner. Sounds like a pain in the a** doesn't it? Every time you get on air, fiddling with knobs. Some people like doing this as if its a skill. I personally think you should resize your antenna to get to a good SWR once and you won't even need a tuner at all. However not everyone has 6 or 7 monobander antennas laying around the yard, and many amateur radio operators use wire antennas on the lower bands, so I understand why sometimes you need a tuner. I still don't like it though.
IS there ALOT of Loss due to SWR??
Is there alot of loss due to SWR in the range of 1.5 to 2 -1 ?? Actually the answer is NO, hardly any loss! So what is all the crying about? Why do you even need a tuner? Again your radio equipment does not want to see ANY reflected power coming back down the coax, because frankly it doesn't have any place for it to go, other then heating up your output transistors that are trying to push RF forward and not recieve any reflecting RF at all. (to be clear some reflects back up towards the antenna) So what is the loss? Well these are lots of tables on the internet to look at, but really if your SWR is 50 - 1, you have blown something up probably and are not reading this. So here is whats relevant:
SWR ratio 1.0 to 1
power transmitted as RF 100% db's lost 0
SWR ratio 1.25 to 1
power transmitted as RF 98.4% db's lost .08 !
SWR ratio 1.5 to 1
power transmitted as RF 96% db's lost .18 !
SWR ratio 1.75 to 1
power transmitted as RF 92% db's lost .3 !
SWR ratio 2 to 1
power transmitted as RF 89% db's lost .5
SWR ratio 2.5 to 1
power transmitted as RF 82% db's lost .85
SWR ratio 3 to 1
power transmitted as RF 75% db's lost 1.25
As you can see if you have a SWR that is higher then 2.5 then you should start to look at ways to correct it, either by resizing your antenna or using a Antenna Tuner. Fix your Antenna. The best way to do this, is to connect an antenna analyzer to the antenna with a short piece of coax, and resize the elements (particularly the driven element) until you get a decent SWR, only then connect your longer length of coax that your going to actually use. Everything else in your Amateur Radio chain is 50 ohms, so correct the antenna first and you are good to go.
Lets DESTROY a common myth. You friend told you or you read that if you cut the coax in multiple of half wavelengths X the coax velocity factor or some other magical formula, it will bring your SWR down. And your SWR meter will even confirm it! Yes, your SWR meter has been fooled! But the reality is, if you can shorten or lengthen your coax and the SWR changes at all it means one thing only..........You have a SWR problem and reflecting waves are traveling back down the coax to your rig and or amplifier. Wanna know what the real magic distance is: Long enough to reach the transciever in your shack, with a few feet left over in case you move stuff around.
Here's how you test to see if your SWR readings are correct and all is fine and dandy:
Run your coax directly from your antenna to your Transceiver ( no tuner in line) note the SWR reading. Take a simple SWR meter or use an antenna analyzer connect it to the coax coming from your antenna and then get a 3 foot jumper cable , put the jumper between your Transceiver and the SWR meter, now read the SWR meter, did the SWR change? Do the same experiment with 6 foot and 10 foot jumper lengths, so the SWR meter is now 6 feet away from the Transceiver and then 10 feet away from the Transceiver. Did the SWR change on the SWR meter? If it did you have some reflected waves coming back down your coax to your radio. If the SWR reading remained exactly the same after all three jumpers were inserted and then removed, congrats you have a very efficient antenna system. And your SWR readings are accurate.
Your Transceiver is 50 ohms, the coax you bought is 50 ohms, these do not change. Whats left to change the readings? Your antenna is not 50 ohms ( although it is certainly a static number like 25, 50 or 100, ohms..... this will be addressed in the section below) or the reflected waves coming back down the coax is changing your impedance.
Fix It.
Is there anything else you can do for Higher than optimal SWR? The first thing I want to say is don't get hung up on 1:1 SWR readings they mean next to ZERO. Think of it this way. Your Dummy Load has 1:1 SWR and how does that work for transmitting? But for those situations where you must transform your antenna into something close to 50 ohms: You can use a Balun. You'll need one of these with wire antennas, some homemade end feds, verticals and even some yagi antennas. Think of a Balun like a remote tuner, in that it is placed at the source of the antenna rather than in your shack. It will transform the impedance of your antenna into or close to 50 ohms and stop any common mode current or reflecting waves from heading down the coax.
Baluns
If there is a ham radio term more confusing and misunderstood then a Balun or better yet a Unun, I haven't seen it. So what does it do and how does it do it? Well there are a few types of Baluns ( OH NO ) , I feel your pain, let's TRY to make it simple.
BALUN....sounds like a combination of the words Balance and Unun. Thats because it is. Baluns were originally made to correct an imbalance. What imbalance? The simple crude explanation is this: In coax the inner conductor and the shield have two different shapes, diameters and are not symmetrical or identical. This means current will flow through them differently (slower among other things). The current on the shield side is not equal (and opposite) to the current on the inner conductor side. This means there is an imbalance. So what? Why should you care? Lets say you are feeding a standard half wave dipole antenna. It is equal on both sides of the feed point is it not? You would want a balanced equal current flowing into each side of it, makes sense? If you do not have that balance, current goes in places it shouldn't.... looking for.... LIKE anyplace to go other than through your antenna. In this case it will run down the coax shield and cause the same issues mentioned in the above section about SWR.
So here you would use a Balun (specifically a current balun) to create a equal (and opposite) current relationship on both conductors. It will also prevent any current from running back down the coax towards your radio/amp. Apparently voltage & current really doesn't like to be forced out of your antenna and become RF, it will try to do anything other than that to avoid become RF. If you look at it that way, you can see the importance of keeping all your hard earned $$$ from dissipating someplace random, and instead making sure your getting it all out through your well designed RESONANT as possible HF Antenna system.
I can hear an objection............ Why not just use twin lead?? Its equal, balanced, symmetrical and identical...so there! tough guy! You could, but it may not fix the problem because now you have a new problem, since twin lead is not shielded, you must keep it away from anything that can conduct electricity. Your antenna, Your tower, other wires near your tower, the angle at which it leaves the antenna tower installation near the ground, the tilt of it near the ground! All the way to the shack! As soon as one side of the twin lead gets closer then the other side of the twin lead, it will couple..... to your sister if you give it a chance. Then it goes into your shack where EVERYTHING you own is metal. Guess what ? This is twin lead coupling paradise. Including a direct connection to your rig, which of course is grounded. What happens when it couples? Well then you have the same common mode current issue that you were trying to avoid. Twin Lead sounds good, but in practice you could be pulling your hair out trying to figure out whats wrong. You might be thinking I am not a fan of twin lead transmission line. You're right I'm not. Yes its cheap, Yes it is supposedly low loss and Yes its cheap. Those are the benefits.
Everyone knows that Twin Lead Ladder Line is much cheaper than coax right? I am going to suppose that you who are reading this right now has the internet, and you probably have wifi and of course 200 channels of television and about 30 apps on your TV ( Apple TV, Amazon prime, Netflix, Hulu...etc.etc.). SO my question is was all of this bandwidth and crystal clear picture quality brought to you by the Ladder Line company or the Cable company. I mean surely the cable company realized they could have saved hundreds of millions of dollars by sending it to you by using ladder line? Why didn't they? Hmmm why did they choose the more expensive cable to do this? The answer should be obvious. In order for you to get all these channels and content in a crystal clear manner with no interference from any other sources outside or inside your house, they needed to use a shielded impedance steady CABLE. I am no fan of the cable companies believe me, but this is the best interference free reception your going to get on your TV. In fact remember when you actually used twin lead as your antenna cable or antenna back in the 60's,70's and early 1980's?? How did that work out for you?
One other thing about ladder line, let me ask you this. Have you ever contacted a super station with multiple antennas on multiple towers? Did you ever ask them if they are using Twin Lead as a transmission line?? OK When the laughing stops continue reading on.....................still waiting for the laughter to stop............ OK, these are stations that spend hundreds of thousands of dollars just on coax! Not your LMR 400 high end coax......No that stuff is for kids. They are spending hundreds of thousands of dollars on the good stuff, LMR1200, you know the 1 5/8" thick stuff. Never seen it? look it up. Its mega expensive. Your high end LMR400 fits inside it, like a baby in a stroller. Don't you think if they could have saved $300,000 in coax they would have by using twin lead?? Why didn't they just do that? BECAUSE Twin Lead is a Pain in the A**. FLAME ALERT>>>>>
I know what your going to say, you built a dipole or something similar and you feed it with twin lead and it works fine. I hear that alot, I also hear this alot more. "Hey my twin lead works fine....."OOPS my SWR just went to 6 - 1" , "Wait its windy outside I better check my twin lead" "Hold on I can't transmit now because its raining and the SWR is high"... "I can't transmit in a snow storm, because you know the SWR" ..."When my twin lead dries out, I will be able to get the SWR down"... "Wait my twin lead isn't properly twisted"...etc.etc.etc. and on and on it goes. Could you imagine being a Super Station and having these excuses??? You would be the laughing stock of Amateur Radio after spending millions of dollars just to say "HELLO" to somebody .... What a let down.
Bottom line is this, if your radio and everything else were to be isolated from ground, the twin lead feed line currents would be hunky dory (equal and opposite), the imbalance would be ZERO and the feedline would not radiate. When your equipment is connected to ground (which it should be) then a 3rd connection is introduced and this creates a current imbalance, whether you have twin lead or coax. Believe me THIS IS the short version of a longer version of techo-nonsense you don't need to hear.. I don't like ladder line for the many reasons above and more and neither should you.
Back to baluns:
Balun number one is the voltage balun, this is two wires of equal lenght wound around a iron donut looking magnet type thing. This is the voltage / impedance transformation balun you see in magazines as 4 - 1 balun, a 9 - 1 balun, a 2 - 1 balun etc., it can transform the impedance from 200 ohms to 50 ohms, in the case of a 4 - 1 balun. It can transform 450 ohm twin lead into 50 ohms, in the case of a 9 - 1 balun. The voltages are running through the wires and are forced into a equal but opposite state, and connection to the antenna can occur, and your lines are now balanced. Theoretically. However if your antenna is not perfectly balanced ( something other then a half wave dipole ), current can and will flow back down one side of the coax. You see current HATES being turned into RF at the antenna and will try at any opportunity to run back down the transmission line (its terrified). In most cases you are okay with one of these voltage baluns with a simple dipole as your antenna. As a side note, you will see various prices on these baluns. Voltage Baluns have to be made precisely correct. Or you will see all kinds of SWR problems at the shack. So don't cheap out, buy a good DUAL -CORE Balun like a DX Engineering one or similar. They are not cheap. But you'll be glad you spent a few more sheckles in the end.
Balun number two is the current balun. (A BETTER BALUN) this is one or two pieces of coaxial cable wound around that same iron donut looking magnet type thing or by placing ferrite beads around the outside of the cable. They both accomplish the same thing. They make a choke by making the shield portion of coax have a very high impedance hopefully like 1000's of ohms (kind of like a road block). What this does is prevent any "wimpy RF antenna terrified current" from passing back down the coax. Current baluns do not change impedance. They are chokes that prevent common mode current as it is called from running back down the coax. Lots of times these are just called a 1 to 1 current balun. In most cases this is the Balun to use on almost any antenna that doesn't require an impedance change. Generally even a 1 - 1 current balun can solve mysterious impedance and current mode problems. These Current Baluns have various names to confuse you: They are "a feedline choke" , "1 - 1 Balun" , "line isolator" , "common mode choke" , "Guanilla choke"...and about 10 other names. They are ALL THE SAME THING........A CURRENT BALUN. BUY A DUAL CORE BALUN AT ALL TIMES, is my not so humble recommendation.
Can you run a Voltage Balun and then a Current Balun right underneath it, at the antenna feed point? Yes you can. These are sometimes sold as complete units Voltage and Current baluns in the same enclosure. Hybrid Baluns is the correct term, however often these will be sold as Current Baluns with the added benefit of impedance transformation. Inside the plastic box you if you dare to open it, you will see the above twin iron magnet thingy. They do a good job and solve the problem all in one box. BUY A DUAL CORE BALUN AT ALL TIMES, is my not so humble recommendation. When in doubt put a choke underneath the balun that you have, and that should help you SWR stability issues and current mode problems ALOT. DO IT.
What is an Unun? Notice there is no BAL in Unun. A Unun is a specific type of balun that is meant for End Fed verticals and Long Wires. In other words for antennas that really don't have any type of balancing on the other side. The antenna itself is unbalanced and the unun provides connection to a unbalanced connection (coax) . So unbalanced antennas to unbalanced coax. Why? They will still prevent common mode current from running down the coax. In fact there is very little difference between a balun and a unun other then the output connection.
A Balun normally is for dipoles , symmetrical antennas, like delta and skywave loops, yagi beams, cubical quad antennas, those antennas are all balanced types. One side is equal to the other in length. Thats the difference between a normal Balun and a Unun.
Basic use for where to use Baluns and Unun's:
Single Band Dipole : most likely you should use a 1:1 Balun
Feeding anything with Ladder Line: most likely you'll need a 4:1 Balun, possibly a 6:1
Ground Mounted Verticals: most likely you need a 4:1 Unun
End-Fed wire antennas: a 9:1 unun followed by a 1:1 Choke
Summary of differences of Ununs and Baluns:
Balanced means both conductors have the same signal, same composition and size. Like a dipole it also makes the feed line less of a radiator (But please still use a choke). Also means that neither side is connected to ground. Because of this balanced lines can be affected by outside influences. Not just signals, but other conductors near them, like other antennas, and other outside noise interference is common on all dipoles and yagi elements. This also includes twin lead feedlines.
Un-balanced means the signal isn't exactly the same on the two conductors because they are of a different size or composition like coax or vertical antennas. The shield is a DC ground. For coax as an example the signal is in the center conductor only. The shield prevents any outside signals (noise) from getting inside. Essentially, the center conductor is a radiator for it's entire length. It's just contained inside the shield so nothing gets in or out .
Balun Loss ---- Unun Loss ---- Matching Loss
Sorry as of 2022, I decided to add this new material, which escaped me some how earlier. ( I'm getting old, its not my fault)
Well there is no free lunch with Baluns, Ununs or any other uns. There is some loss using baluns, and sometimes its not pretty. If you try to look up elsewhere on the internet, you will undoubtably never really get a straight answer. Of course you can go to a famous blogger's page and get your technical jargon fix if you want, but you probably still not going to be satisfied. So after doing this myself, I decided to run my own testing.
How did I do it? Simple: Place your Balun or Unun in line with your transceiver and good digital watt meter, measure before and after the insertion of the balun/unun in line. You must place the 50 ohm side of the unun towards the watt meter. So the watt meter receives 50 ohms into it from the balun/unun. Also make sure you press the tuner button on your transceiver to make sure the SWR is flat to the watt meter. If you have great flat SWR all the way to the wattmeter when you begin, you may not have to press the ATU.
So what are the results? A couple of general conclusions can be made. First most Baluns made by the online sellers you see on the internet are decent none were absolutely terrible. Again in general the efficiency was around 84 - 96 %. Sounds good right. Well not really. I noticed that manufacturers quote numbers like .5 db loss, that is if they even quote them at all, most don't. That number sounds good but .5 db loss is 12% of your power! But if you sold online.... baluns or ununs wouldn't you rather say the loss was .5 db instead of saying you'll lose 12% of your power!
You'll hear on the internet that the higher the power rating of the balun the lower the loss, this makes sense to me but wasn't necessarily true. I also have heard the more the transformer ratio...like a 9-1 balun versus a 1-1 current balun the more loss there would be. This does seem to be the case. However some baluns are more expensive and have more than one core inside, these did do better in testing. As an example DX Engineering baluns were the highest efficiency of all of the ones I had. Palomar, Balun Designs, W2DU, DX Enginnering, were all tested and quite a few others, most anyone you've probably seen online I had. In general the results somewhat surprised me. There is a fair amount of loss when using Baluns/Ununs no matter who makes them. To sum up: The more toroid cores are used like 2 or 3, the better your chances of getting a higher efficiency balun/unun. Also the greater the transformation to 50 ohms you make the higher your typical losses will be most likely. As far as different frequencys from 80 - 10 meters the lower in Frequency you went the less loss.
Now what about 1-1 common mode choke ununs and the like for common mode interference? Well they worked best of all. The common mode choke that worked the best was ferrite beads. But I think you'll need alot of them (like 20.... in my humble opinion) to get the impedance high enough on the coax shield to stop any common mode interference. As for dual toroid type common mode box chokes, they had close to 96 - 98% efficiency!
Amplifiers & Tuners
Amplifiers and Tuners Together?
Most amplifiers already have a tuned input circuit so there is no need to add an additional tuner since maximum power transfer from your transceiver to the amplifier is already being accomplished. Solid State linear amplifiers have a fixed output impedance and generally require a tuner to follow them or they will not attain full output power. Sometimes Antenna Tuners are called "automatic" in that they have a tuner inside, so you don't have to fiddle with the knobs yourself. Some times these "automatic" tuners work well and sometimes they don't. They work but may not get you the optimum SWR you are looking for every time.
Tube amplifiers have a tuning section (very similar to your antenna tuner) after the tubes which serves the main purpose of matching the output impedance of the tubes to the impedance of the load (antenna) . If your antenna system presents a reasonable impedance of less than about 3:1 to a tube linear, then the tune up process of the amplifier IS the antenna tuner and you don't need another one.
For highly mismatched systems, the tube amplifier will not be able to tune because the mismatch is too large and an additional tuner is needed. This is where you should re think what you are doing and fix your antenna, or balun that sucker, or else at some point your going to have your amp on, and your tuner on bypass and guess what??? Large Loud Explosion followed by No More Amplifier. Fix your Antenna before you get to this stage and I promise you, you will save alot of money.
As far as adding additional pieces of equipment that make for a great QRZ.com shack picture, every place you add equipment in your coax sequence, it introduces some loss, so putting a tuner and anything else in line where it is not needed kills your recieve, robs you of some power and is another potential place for noise to enter without giving you anything in return. If you bypass your tuner and your amplifier will still tune up, you are good to go.
1500 Watts Input power....A zillion Jumpers.......Output Power ZERO
