HOMEBREW HEXBEAM PAGE
by W1GQL

 



 

 

 

 

 

Gain

     Hardly a week has gone by in the last 51 years that I have not thought about antennas.   Most of those years I have thought about how to build antennas that work fairly well and cost next to nothing. Until I built my first Hexbeam I have not had an HF antenna that would rotate since I was in the 10th grade in high school and my grandfather found a telephone pole beside the road and put it up in my backyard. I made a 15 meter 3 element yagi and he and I somehow managed to get it to the top of the pole. I turned it with ropes that came into my bedroom under the window sash. Since then, except for a couple 2 meter antennas, all of my antennas have been some sort of wire arrays. For years I used a ZL special for 20 meters that I loved. Only problem with it was that it was in a fixed position.      One of the things that I think about when I am considering a new arrangement of wires   in the sky is GAIN. In fact, I have thought a lot about it and done some considerable reading about it (especially when it is winter and stringing wires outside in Maine is not as tempting as it is in the summer -- I have done it though!!) I want to share with you some insights that I have on gain and then get straight to information on the gain of a Hexbeam. Bear with me, please!

 

  • No matter how good an antenna you have, the antenna does not magically magnify the signal that you put into it! You never get more out than you put in. In fact, due to wire losses etc., you never get out even as much as you put in.
  • All "gain" is achieved by sending more signal out in one (or more) directions. This is done at the expense of signal going in some other direction. In other words, an antenna with gain merely "subtracts" from the signal in some directions and "adds" to the signal in other directions. We have to keep this in mind.
  • An antenna may have "excellent" gain, but that gain may be going off in a direction that is not very useful to us. Or it may have gain going off at the wrong "take-off angle". If that gain is shooting straght up or at a high angle from the horizon, the signal will either not bounce back to the earth or will bounce back too close to us and never reach the dx station we are calling.
  • Gain is measured in decibels, something that are a bit hard to understand for most of us. It pays to get a grasp on the concept of the decibel. An increase in signal strength of one decibel is the smallest increase that a human ear can supposedly hear. Personally, I don't think that I can hear the difference very well myself. As far as hearing is concerned, it is a VERY small difference.
  • Another way to look at a decibel is to realize that if I double my power I will gain only three (yes 3) decibels of power. If I am going from 10 watts to 20 watts or from 500 watts to 1000 watts this is the case. One of the most enlightening things a ham can do (every ham should be required to do this!) is to listen to signals on one of the dx beacon frequencies such as 14,100 or 17,110. On these frequencies stations around the world as taking turns sending out signals. First they send their calls and then send a tone at 100 watts, then at 10 watts, then at one watt, and finally at 1/10 of a watt. What will shock you is that there often does not seem to be any difference between adjacent tones. The 100 watt tone does not seem much different to the ear than the 10 watt tone. And yet the signal strength has been cut in half 3 plus times. That means that the 10 watt tone is over 9 decibels lower than the 100 watt tone and yet it sounds about the same. KEEP THIS IN MIND AS YOU WORRY ABOUT WHETHER AN ANTENNA YOU ARE CONSIDERING OFFERS 2 DB LESS GAIN THAN ANOTHER ANTENNA.
  • People also judge or compare antennas using S meter readings. One thing I have learned over the last 50 years is that S meters vary all over the place, and even vary considerably from band to band in one receiver. Also bear in mind that, especially among CW ops, the S part of the RST is usually a human judgment call and is not to be relied on for serious antenna comparisons. I wish I had a nickel for every time I got a 599 and then was asked to repeat my name and/or qth. Generally we are told to think of one S unit being 6 decibels. That means that if my signal strength is doubled and doubled again, either by my "cranking up" the rig higher, or building an antenna that will boost my signal by 6 more decibels, it will only raise my signal strength at the other end by ONE S UNIT. Knowing that little fact should really make you think.
  • There are theoretical maximums to the gain any type of antenna can display. I guess that the only way around those maximums is to come up with a new "type" of antenna. Some people seem to feel that the Hexbeam is one of those "new types" that might be able to beat the maximum known gain. I had a very long interesting phone conversation with Mike Traffie, the inventor of the Hexbeam, last fall and I got the feeling from him that he thinks he may have hit on one of those new types. I don't blame him, because the Hex is a remarkable antenna. Mike told me that he had been able to make some signal strength measurements at different points around a working Hexbeam and that he found the strength of the signal around the apex, or points, of the "W" to be different than the theories predict. I wish Mike well in establishing this point, but for the time being I personally will continue to consider the Hexbeam to be a 2 element yagi with bent elements and a 2 element yagi has a free space gain maximum of about 5 decibels over an isotropic radiator.
  • Gain works both ways. That means that if your antenna shows 6 dBi of gain while transmitting in a given direction, it also shows 6 dBi receiving as well. And if it shows poor gain in a direction, it will receive poorly in that direction as well. A lot of times I take advantage of that fact and turn my Hexbeam to null out an offending signal instead of peaking it on the signal I want. Sometimes you can pretty much eliminate the interference by doing this. We will see that the Hexbeam has a rather wide signal in the forward direction, so that turning it so that it does not aim directly at the desired station makes little difference is that signal's strength.

 

     Having read all those comments, I suppose you think that I was "setting you up" to  accept some low gain figures for the Hexbeam. Actually that is not the case. The Hexbeam shows respectable gain. I do want the reader to understand gain, however, as I go on in my discussion of the Hex, especially when I deal with height issues.      This web site feature a 20 meter Hexbeam that I built after extensive   modelling on my computer using EZNEC. Let me show you some of the information on this antenna using EZNEC printouts. Antennas do not always live up to their computer model twins, but I think mine does or at least comes close. I have no reason to think that my actual Hexbeam behaves much differently than the computer model shows.

 

     For illustration purposes I am using EZNEC screens from my model of my 20 meter  hexbeam.

 

     First let's compare the Free Space Far Field Patterns for a 20 meter dipole and a 20  meter Hexbeam. Use the Browser Back key to return here.

 

20 Meter Dipole in Free Space

 

20 Meter Hexbeam in Free Space

 

     Note that the Dipole shows 2.17 dBi gain perpendicular to the elements.  This is 2.17 db of gain over a simple isotropic (vertical) radiator which radiates the same in all directions. Also note that the Dipole shows very little radiation off the ends. It has a poor front-to-back ratio, but good front-to-side.

      The Hexbeam shows 5.07 dBi of gain in the forward direction and -13.2 dBi directly to the rear. That is a front-to-back of 18.27 or about 3 S units. The 3 db gain over the dipole in the forward direction is the same as doubling the transmitter power.

     Now lets look at a 20 meter Dipole vs. the 20 Meter Hexbeam, both at 30 feet. 

 

20 Meter Dipole at 30 feet

 

20 Meter Hexbeam at 30 feet

 

     Note that the Dipole shows a gain of 6.66 dBi and the Hexbeam a gain of 9.31 dBi.  (Raise it a three feet if you want another half dBi of gain.) The maximum radiation of the Hexbeam is at a slightly lower take-off angle than the Dipole's. Again we have the equivalent of about a doubling of power, but now we have the great advantage of transmitting AND receiving at 14.12 dBi less gain at the rear. The gain to the rear is -4.44 dBi or 4.44 db LESS than a omni-directional antenna would. High gain in the forward direction is NOT THE ONLY advantage of a beam. Here is another plot of the Hexbeam's output looking from above. Note that the signal is fairly wide. This makes aiming the Hexbeam fairly easy. I have had seen antennas with fantastic gain, but they were very, very hard to turn in just the right direction and you constantly had to adjust their positions. I can aim my Hexbeam toward Europe and work all over with out ever touching the rotor control.

 

20 Meter Hexbeam at 30 feet ("top view")

 

     Now for the true test of the Hexbeam. Here is the plot of a 2 element Yagi beam with conventional straight elements at 30 feet.

 

20 Meter Two Element Yagi at 30 feet

 

Look familiar? It should. It looks almost identical to the Hexbeam. Even though the Hex has its driven element and its reflector bent back and forth the Hexbeam holds its own again its close cousin, the 2 element straight element yagi. And rememeber that its turning radius is less than 10 feet. The 2 element straight element 20 meter yagi has a turning radius of over 18 feet! And it weighs MUCH more and requires a much more substantial rotor.

     And finally here is the plot of a five (5) element yagi at 30 feet. Note that its gain is only   about a half an S unit more than the Hexbeam and it looks very similar to the rear. Still think you want to put up a big yagi on an expensive tower instead of a little "upside umbrella" on a push up pole?

 

20 Meter FIVE element Yagi at 30 feet

 

     (In all honesty, if Santa managed to get it past the xyl, pocketbook, and neighborhood  tests, I would not turn down a 5 element Yagi at say 75 feet. I could use it as a standby antenna! Click here to see the plot of one. It is not perfect, however. Look at the forward gain at a take off angle of about 26 degrees. It is about -2 dBi or almost 2 S units below what my Hexbeam puts out!!)

     Gain on any Hex drops off slightly as you go up in frequency in the band.There is also   a lot more signal to the rear -- two reasons why Front-to-Back drops off as you go up the band as well. If you don't plan to operate CW at all you may want to cut your Hex to resonate higher.

 

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20 Meter Hex at 14.0 and 14.3

       

 

SWR

     We all are concerned with SWR. That is kind of odd in a way when you realize that in  the mid fifties when I got my General ticket I can't remember even having heard about SWR. My rig used Pi-net tuning and my antenna was a 125 foot length of wire from a pole in the backyard and coming right under the sash of my bedroom window and straigt to the wing nut on my Walter Ashe kit 25 watt rig.

      We have to remember that there are some wonderful antennas out there that radiate  beautifully but have astronomically high 50 ohm SWR. They work great, you just can't run a coax directly to them without some sort of matching section between the coax and the antenna feed point.

     My point is that antennas don't have to match 50 ohm coax to be good antennas.   It just makes it a heck of a lot easier. Another thing to remember is that the best configuration for gain does not have to be the same configuration for best SWR. And it certainly is not always that way. Most antennas out there involve some compromises to get gain and SWR both where we want them. One of the great things about the Hexbeam is that very little compromise is necessary. Good News! All three of the homebrew Hexbeams that I have built have had great SWR across the ENTIRE band. And that is without really trying. Here is the SWR curve of the model of my 20 meter Hex.

 

20 Meter Hex SWR Curve

 

     When we talk about Front-to-Back later on, I will point out that if you can tolerate  an SWR closer to 2:1 at the bottom of the band you will get better Front-to-Back. Models of Hexbeams and actual hexbeams all show SWR curves that drop much more steeply at the bottom of their range than they do at the top. The models also all show that the best gain and the "best" swr are offset slightly. In fact, I have seen models that showed very low SWR way above the top of the 20 meter band, and that is a fairly wide band.

     By the way, if you build a Hexbeam, don't start pruning the elements trying to get the  SWR down if you only have it on a test stand, say at 10 feet. The swr will drop when you put it higher. Wait till you get it up at least 20 feet or so before you decide you have to play with the element lengths.

     I must recommend to you that you look into buying or borrowing an antenna analyzer. I consider my Autek RF-1 the most valuable piece of test equipment I have. It sure beats having to to test the SWR of a new antenna by firing up the rig. In just moments I can see the SWR curve of a new antenna without leaving my backyard. Beg, borrow, or buy one!

     Also take note that some rigs are much more forgiving of higher SWR's than the manual indicates. An SWR reading of 1.5 on the RF-1 meter translates to 1.1 when my Icom IC-706 sees it. If your relatively new transceiver does not start to automatically cut your power back for you when it sees your antenna you can probably go ahead and leave the antenna the length it is and operate. I guarantee you that the losses working into any SWR under 2:1 on HF are so minimal that worrying about them is not worth it. Go ahead and have fun. As long as your rig likes it, why should you worry. No one will know, ever! The losses at HF frequencies are pretty much negligble. (Not true at VFH frequencies and up.) Return to Top



 

PATTERNS

     I like the pattern of radiation of my Hexbeam. I have see some that I don't like. Say that   of the 5 element 20 meter yagi at 75 feet I mentioned earlier. Here are the 3-D plots of both of their patterns of radiation and I think you will see what I mean.

 



20 Meter Hexbeam 30 feet

 

20 Meter 5 Element Yagi at 75 feet

 

     Sure the 5 element Yagi throws a nice signal out at 12 degrees above the horizon  but what about all that stuff going in the other odd direcions. See what I mean? Looks like I could work the DX coming in a a low angle fine, but signals coming in at a higher angle would take quite a hit. I would rather see a more evenly distributed pattern. In all fairness I think we should look at what happens to the Hexbeam's pattern as the height above ground increases.

 

20 Meter Hexbeam at 30, 40, 50, 60 feet

 

     The pattern of the Hexbeam becomes just as messy. I admit it. But looking at the  difference helps me understand why Mike Traffie, the inventor of the Hexbeam, feels that it is not really worthwhile going to the effort and cost of putting the Hexbeam higher than 30 to 40 feet. Makes sense to me. The improvement in gain is only 1 dBi!! Remember that 1 dB is the smallest difference in a signal that a human can detect! The only real gain is in a lower takeoff angle. But a takeoff angle of 16 is still not in the range the "big gun DX men want. They are looking for 11 or under. So why pay for a tower twice as high for one dB gain in signal and a takeoff angle still far from ideal and a lot of my signal going off at crazy angles? I wouldn't!!

      In fact, I have had wonderful success with one of mine at 28 feet. Have worked the world, gotten 90% of the people I call on the first call, and for the first time in my life have had DX stations calling ME one after the other. My portable Hex made with fiberglass "Crappie" fishing poles is at 20 feet and I have had them both up in the backyard and been able to compare them by just throwing a switch in the shack. I have yet to see any meaningful difference.

     I got an email not long ago from someone who worked in a contest thinking he was using his beam on a tower for 18 hours and he was really, by mistake, using a Hexbeam at 3 (yes, three) feet that he had been testing. He worked 45 states during the contest. I have a similar story. My very first qso on my first Hexbeam was with the Hex sitting on a 7 foot ladder in my backyard. It was with Antarctica. My very first qso with my 17 meter hex, again on a test stand, was with Japan. And we are talking 2004 when the propagation had fallen considerably from its peak at the top of the sunspot cycle. Return to Top

 

FRONT-TO-BACK

 

     Hanging beside me on the wall of my shack I have a scrap of copy paper that I tacked   up there during the first few days I had my Hexbeam. For the first time ever I had an antenna that I could point toward South Africa and I was thrilled to work Vidi, ZS1EL, not once but twice. The paper on my wall has the CW copy from Vidi who was kind enough to take the time to let be swing my Hex around, first toward him, and then 180 degrees away from him. What he reported was that I was coming in at 6 to 7 on his meter with the antenna aimed at him and 3 to 4 with it aimed away from him. Ever since then, whenever I have had a chance to ask someone for a comparison or just turned the antenna while listening around, this is about what I have seen. Three S units. Sometimes the report will be 559 or 569 with the antenna turned away and 589 or 599 with it aimed right at the station. I am pleased and think you would be, too.

      A lot of times it gets even better. A station that is really "in the mud" can be floating high and dry at S-8 or S-9 when I swing the Hex on them. An S unit, you will remember, is supposed to be 6 dBi. (Remember that that many S meters are not really callibrated very well.) Three S units is then 18 dBi. That means the signal strength is doubled 6 times, since it doubles once for every 3 dBi. If I have the back of the Hexbeam aimed at a weak sounding station and turn the beam toward it the weak station will be 64 times as strong (1 doubled once become 2, then repeatedly doubled 5 more times first become 4, then 8, then 16, then 32, then finally 64.) Even if the S Meter were so far off that an S unit equaled only 3 dBi, half of what it theoretically is, then the typical 100 watts signal would double only three times and would be the equivalent of an 800 watts. Not bad, in any case. And remember the same thing happens to my transmitted signal!

      We must remember that these figures represent a comparison of the signals from the front and back of one antenna. How do they compare with the signals from my old dipole. We have seen that a Hex is about 3 dBi stronger than a dipole if you compare their most favorable directions. So our signal will be twice as strong as in that direction than it would be using the dipole. But wait! The dipole does not work well off its ends. In fact its gain off the end is maybe 9 dBi less than it is perpendicular to the dipole. Since my Hex can turn 90 degrees and transmit in that direction that the dipole does a very poor job on, then the Hex has about 12 dBi gain over the dipole in that direction. My Hex signal would be 16 times as strong in that direction than my dipole. Can you see why I like it?

     The best Front-to-Back figures for any Hex are at the low end of its range where the SWR  is on a sharper downward slope, as we have already seen. If your rig will tolerate an SWR of close to 2:1 then make sure your Hexbeam is cut to place the 2:1 SWR point at or just below the lowest portion of the band you will be operating. This is the reason Mike Traffie offers a version of the 20 meter Hex cut for the phone band.

 

20 Meter Hexbeam at 14.0 and 14.3

 

     Admittedly, working Europe from the Coast of Maine where I live is not difficult, but I have been thrilled on more than one occasion to have a European tell me that my signal is the loudest on the 20 Meter CW band. A "magic" antenna? Well that's "magic" to my ears. A bunch of wire rescued from the dump, a piece of plywood I found in my junk pile, some twine, and a friend's old quad spreaders, a few bolts, a little time, a lot of fun and I have a wonderful antenna. I hope you enjoy yours as much as I enjoy mine. It is by far the best antenna I have had in over 50 years of hamming, bar none. Return to Top

 




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