Ham Radio Antenna Gain
So what is Antenna Gain and how can I make the most of it? Antenna db gain is based on what an antenna might do versus a half-wave dipole antenna in Free Space. Antenna DBi gain is based on what an antenna might do versus a isotropic antenna. What the h*ll is a isotropic antenna? Good question. In antenna theory an "isotropic antenna" is a hypothetical antenna radiating equally and of the same intensity in radio waves in all directions (360 degrees). Think of a tennis ball as the radiation pattern of a isotropic antenna, It is said to have zero directivity and therefore a gain of 0 DBi. Is there such an antenna as an isotropic antenna? NO. Its a mythical creature never to be advertised in any magazines, or out up on any towers. It doesn't exist. So then how does a half-wave dipole have 2.15 dbi versus a isotropic antenna, if an isotropic antenna doesn't exist? Good point. Well the answer is by the radiation pattern of the antenna. An isotropic is assumed to be complete round circle in radiation patterns, where as a half-wave dipole actually has some directivity to it, and therefore some antenna gain. See above and below for details.
Ok lets turn it Horizontal and maybe this will look familiar.
AAH, there we go, a horizontal half-wave dipole in Free Space. You can plainly see it radiates in mostly two directions and therefore must have some gain. How much? 2.15 dbi . So says the Isotropic gods. So all antennas should referenced in gain either versus a isotropic antenna ( 0 DBi ) or a Half-wave Dipole ( 2.15 DBi ). Aren't they referenced this way in magazine and book articles when referencing gain? Not necessarily. In fact almost never. You see the above references are in Free Space. Ok, so what the h*ll is Free Space? Free Space is kind of like isotropic, in that it doesn't exist. OH Boy, getting confusing? Its not. Since an isotropic radiator doesn't really exist ( since no real antenna could be made to have a perfect circle of radiation ). Free Space represents what a antenna radiation pattern would look like with absolutely nothing around it. Meaning no trees, no ground, in fact no earth ! Nothing.......it is radiating in Free Space. In reality all antennas become affected by whats around them, Trees, Type of ground, Earth topography and most importantly Height above the Ground. You see lets say you are an antenna manufacturer and you want to make your antennas look like they have alot of antenna gain ( Gee who would do that? ). The way to make your antennas look like they have alot of gain is to say " this antenna has 10 dbi of gain ". What they are failing to mention is that they don't say what the antenna gain is referenced against most times... A isotropic radiator?. It is supposed to be that, but at Free Space? Most likely they forgot to mention that their 10 dbi antenna was most likely not measured at Free Space, but at 100 feet in the air!! Somehow antenna manufacturers ALWAYS forget to tell you exactly what they were measuring against. What a surprise...NOT. This is why if your serious about learning about
Antenna Gain
You should take up EZnec modeling software and get the real story on what your antenna provides as far as gain, as well as what the pattern looks like for it. Antenna manufacturers are selling their antennas, just like used car salesmen are selling their cars. So you are probably not hearing the 100% truth in either case. Don't believe them, check with Carfax or get yourself up to snuff on EZnec and you'll know exactly or pretty close as to what you are buying.
I decided to be fair in this paragraph to some of the more honest antenna manufacturers. If you can believe there is such a thing. Antenna manufacturers have other things to consider when designing antennas besides gain. Bandwidth across the designed frequency is one. Front to Back ratio is one. Angle of forward radiation is another. Beamwidth of the antenna pattern is another. Physical size is also a consideration. The physical strength to allow antennas to endure bad, windy, rainy, snowy and overall crappy weather is another. All of these things for an antenna manufacturer have to be taken into consideration. As well as the simple fact is they are dealing with consumers who are not nearly as knowledgeable as they themselves might be. So the final product has to be ABOVE ALL made simple enough to build so the average guy can build it without too much trouble. Or else risk a bad review on ehams.net. The SWR has to be close to 1.1 when finished or else risk another bad review on ehams.net. All of these factors generally put the antenna manufacturer in a compromised position when building a marketable consumer antenna. Antenna Gain while important is not nearly their first consideration. Antenna gain you see in pages of magazines or even on many manufacturers websites is mostly just marketing , it is an item few amateurs really understand (other then the higher the number the better) so they get to fudge it a little by not referencing it against anything accurately. Again another reason to take up antenna modeling software to see for yourself what's up.
OK, so lets switch gears a little bit.
1. So what is the most useful gain a antenna can have?
2. What are the average differences in gain between antennas assuming the same height above ground?
3. How much is alot of gain anyway?
4. Is getting 1 DB more of gain worth it?
5. Whats the relationship between gain and your radio's "S" meter?
6. Vertical Antenna versus Horizontal Antenna Gain
7. Will the NY Jets football team ever get to the Super Bowl again?
I want to preface this by saying : Here are some ROUGH guidelines, Different installations and ham radio antenna manufacturers can lead to wildly different results. These estimates should be in no way assumed to be hard and fast rigid rules as far as ham radio antenna db gain. Every ham radio antenna and most importantly placement of the amateur radio antenna or in many of the cases cited below, the ham radio wire antenna....will have a different impact on your results, please keep that in mind, when looking over these ROUGH guidelines regarding ham radio antenna gain.
1. The most useful gain an antenna can have, is related to where geographically you want to make contact, and if your antenna has gain in that direction and at the right angle to make the contact. Alot of this is related to the Propagation page of this website, so I am not going to repeat that entire page here. But in a nutshell, you want gain from your antenna where you can use it most. Most times it means putting your antenna up as high as possible. As a long standing rule of thumb: If you double the height of your antenna you will gain 6 db gain! That means if you had an antenna at 25 feet and decided to put it up on a small tower to 50 feet of height, you'll gain 6 db! That is ALOT. A couple of things come into play here. The farther you get your antenna away from the ground the better, you eliminate ground losses. Number 2... The higher your antenna is the lower the angle of radiation your main forward db gain lobe is, this gives you more db gain where you need it, closer to the earth's surface, good for DX signals and even better for groundwave signals. In general if you place your antenna between 1 and 1 1/2 wavelengths high, you will escape most of the ground losses and this is usually good enough for hams without big super station towers. If you wanna put up a 200 foot tower, by all means do. But for the vast majority of hams with homes that have nosy neighbors.... 1 - 1 1/2 wavelengths in antenna height should suffice to get decent db gain out of your antenna, and eliminate most of the lower annoying noise around your house. See the Propagation page.
2. What is the differences in gain between antennas of the same height? Lets say 50 feet. Again every installation is vastly different, but we can make some general assumptions. This is NOT absolute and entirely accurate (it can't be) so don't bet the ranch on these figures. But Lets say for popular antennas:
You have a sloper wire antenna and you replace it with a Horizontal rotatable half-wave dipole? you'll gain about 4 db or more of gain in the favored direction of your choice.
You have a inverted "V" antenna and you replace it with a Horizontal rotatable half-wave dipole, you'll gain about 3 - 5 db more of gain in the favored direction of your choice.
You have a Horizontal rotatable half-wave dipole at 50 feet, and you decide to replace it with a full wavelength loop antenna at the same height, you'll gain about 2 - 3.5 db gain more with the loop, and you will have also have MUCH less noise, especially true on the lower bands 20 to 80 meters.
You have a 1/4 wave vertical antenna with radials on the ground, and you suddenly decide to buy a $8 million dollar beach house and now you place the same antenna above salt water, you'll gain about 6 - 10 db more gain then when you lived on average soil level ground. $tart saving now.
You have a trapped 3 element Yagi 50 feet above the ground on a tower and you switch to a monobander ( 1 band ) 3 element Yagi antenna of the same height and boom length. This is a tricky one, because trapped antennas vary greatly in quality, but on average you'll gain anywhere from 1 - 2 db gain. Depending upon your installation.
You have a trapped multiband vertical elevated 50 feet above the ground and you replace it with a 3 element monobander Yagi antenna at the same height. Now were talking, you'll on average gain about 8 - 10 db minimum in the desired direction of your monobander beam.
3. So how much is alot of gain anyway? 8 - 10 db of gain is alot, which can only be had by using better antennas and more height. Notice I didn't say using a bigger amplifier? If you double your power from 500 watts to 1000 watts, you've gained exactly 3 db of gain. This is real measurable gain, not some isotropic free space hippy concept. So lets read on................
4. Is getting 1 DB more of gain worth it? Its turns out when Alexander Graham Bell was inventing the decibel, he decided that ONE decibel would be the smallest unit of measure that one could hear between two sounds in loudness. So if you want to be able to detect a slight difference between two sounds arriving through your radio speakers, one decibel would be it. As mentioned above if you double your power level the gain increase is 3 decibels or 100%. Can you hear and see if difference between 3 decibels. OH YEAH definitely. 3 decibels of gain you will certainly be heard much better and more importantly you will hear them alot better assuming you used a better antenna to get the 3 DB of gain. So 2 decibels (approx. 66% more gain) will make a BIG difference between hearing that far away station and not hearing them at all. So is getting 1 Db more of gain (approx. 33% more gain) worth it? The answer is up to you. I say most definitely YES. But I'm not you and that answer is still up to you. And you don't have to get a giant tower and a giant antenna to grab a few decibels. Better Coax can make a huge difference. You'll get 1 - 2 DB more gain in lower noise and more power output, especially on long 100 + foot runs of coax in the higher HF and VHF/UHF frequencys. Moving your antenna away from your house might give you 10 - 20 DB more of recieving gain ! Sound like its worth it? Again antenna height above ground gives you a minimum of 5 db gain as soon as you get any horizontal antenna 1/2 wavelength above the ground versus free space dbi. All very worth it. So is it measureable? Yes
5. What's the relationship between gain and your radio's "S" meter? Its complicated. Many years ago pundits once said, ONE "S" unit equals 6 DB gain" ! Boy is that usually far off from reality! Many Amateur Radio's today are closer to ONE "S" unit equals 3 DB gain. Remember the saying "I have a tight meter" . Now almost everybody has a loose meter. Why? Leave it to those tricky manufacturers. So amateur radio station number 1's meter only moves from S-8 to S-9 in signal strength every 6 decibels, but amateur radio station number 2's meter moves from S-8 to S-9 every 3 decibels, whose reciever appears to be the better reciever? Correct number 2 appears to be the winner. Even if both recievers hear about the same in sensitivity, the one with the "loose" meter will appear to be the better reciever. So slowly but surely the "S' meter measurement has now been taken out of the official manufacturers specs! It used to be in there, not anymore. I personally lean towards the 3 decibels equals 1 "S" unit side, for "S" unit ranges between S-3 and S-9 signals. Signals below that are highly variable IMO as to their relationship with different "S" meters. As well as signals S-10 to S-40 are also difficult to qualify whether an increase from one to another means 3 DB gain or 10 DB gain. Also everyone has a different "S" meter calibration usually. "S" meter readings can give you some measurement differences, but whether the station you are trying to hear is S-3 or S-9 it doesn't matter much. Its whether you can hear them better than you could before that matters.
6. Vertical Antenna versus Horizontal Antenna gain. This is another subject of much discussion, with arguments on both sides sometimes being pretty convincing. So for this I am going to defer to W4RNL (sk) who was the foremost authority on EZnec and antennas. His research has been backed up quite a few times in real world experience by other noted authors. So lets show a diagram first then we'll commence the coffee talk.
The first thing you will notice is that SALT WATER RULES, if you can live near the ocean do it. And I mean you have to be very close to the ocean, like within 100 feet. Hmm. Okay start buying lottery tickets now for that beach house. Other then that on average ground verticals really don't do that well in gain, but they have very low angles of radiation with the gain they have. It ain't much, but at least its at a great dx angle. Horizontal dipoles or otherwise (yagis) they have alot more gain over any ground, including average ground, but the angle of radiation is a bit higher. WHY? Horizontal antennas have the ability to absorb ground reflection RF (since they are horizontal) and this RF reflection contributes usually to about 5 - 6 db more gain at 1/2 wavelength heights then verticals. WHY? Vertical antennas stand straight up (DUH Bill), so this ground reflection passes right by them and does not get absorbed and re reflected, so no additional gain gets added. (admittedly the previous statement I simplified the technical reasons quite a bit, but you get the idea hopefully). This is true for not only Dipoles but also all Yagi Antennas. So always use a Horizontal antenna? Not necessarily.
On 10 -20 meters a horizontal antenna will usually beat up on a vertical antenna ( for DX contacts ) because this assumes you can probably get the horizontal antenna up at a reasonable height, even if its just a dipole. At exactly the same heights a horizontal antenna will always have around 5.5 db gain more then a vertical. Thats a good amount of db gain more. And most noise on these bands are vertically polarized, so you will also have less noise. Although noise is a highly irregular thing, and horizontals being quieter is not always true, it depends alot on your local situation and your neighborhood.
On 160 & 80 meters, you just can't usually build a yagi antenna or a rigid full half wave size dipole, nevermind trying to get it up at least a half a wavelength. (260 feet on 160 meters!). So here certainly verticals have there place, as even if you did get some sort of horizontal antenna up off the ground its radiation pattern would be straight up. So verticals win here easily.
You forgot 40 meters. No I didn't here's where the discussion (or should I say yelling) gets louder. On 40 meters verticals can work well for DX again because the radiation angle is low, however horizontals have more gain, but most of it is at high angles. Lets look at a chart below to further explain.
The blue line is the Vertical ground mounted with alot of radials. The horizontal dipole is 1/2 wavelength up and it is the red line. It has more gain most of it at a high angle. However at the low angles it has about the same gain as a vertical. Not Much. So this is why, some when asked this question, scream VERTICAL ANTENNA and some scream HORIZONTAL ANTENNA. They both can do well, if you can get a dipole above half a wavelength in height above ground (65- 70 feet) it will bring the radiation pattern down as to outshine the vertical. Now if you can put up a 2 or 3 element 40 meter Yagi. #1. I am jealous of your property! #2. You will have more gain then the vertical antenna at a low angle even if you can't get the antenna up to 65 feet. Better Antennas usually mean more gain at any angle.
7. Will the NY Jets football team ever get to the Super Bowl again? I think we all know the answer to that.
Some final thoughts about gain................. Better Antenna versus Bigger Amplifier
Bigger Amplifier Pros and Cons.
1. The same people who hear you now will hear you better.
2. The other people who you can't hear, will hear you louder. ( no more contacts then before )
3. You can heat up your shack or room in the winter without turning on the heat.
4. You boost your ego.
5. You might need a tuner.
6. You will need more coax and coax jumpers.
7. You may need to install a 200 volt special line , or at the very least a power supply.
8. You will have lots of fan noise.
9. Its very expensive to buy wattage.
10. Even more expensive to repair. There's lots of stuff to tune every time you get on the air and you could even damage your expensive radio and your antenna.
11. You seriously could or will get cancer or some other weird disease with close contact to a big amplifier.
Better Antenna Pros and Cons
1. The same people who hear you now will hear you better.
2. The other people who hear you now, you can also hear them now ( you can MANY make more contacts ).
3. You boost your ego.
4. You don't need any more coax.
5. You don't need to install any expensive 220 volt lines or get a power supply
6. You have no fan noise. But it might be a little chilly in the shack in winter.
7. Its expensive if you break it, but thats rare and once you tune it once your good forever.
8. You can get much higher DB gain with a good beam antenna, then you EVER could ( in your favored direction) with just a amplifier.
9. You can enter a DX contest and actually have a chance of winning. You make more contacts because you can hear stations nobody else can.
10. No expensive doctor or hospital bills, while they try to figure out what's wrong with your health.
11. You have to put it outside! And as everybody knows; no one leaves their house anymore to do anything outside! Besides it could rain. SCARY.
The Ultimate test of an Ham Radio Station, is not whether they can hear you, but whether you can hear them.
