Optimised Six-Metre Yagi Optimised Six-Metre Yagi by Brian Beezley, K6STI, Issue 39, October 1993 Here's a design for a 5-element beam on a 23-foot boom with an unusual combination of performance characteristics. This Yagi comes within 0. Amiga Emulation Disks Download Google more. Red Orchestra 2 Non Steam Crack Free there. 2dB of the maximum gain possible on the boom length while keeping all back lobes 20dB down. This performance combination is very rare.

The trick was to optimise the design over a narrow frequency range, 50.000 to 50.250MHz. Many 6-meter beams, both homebrew and commercial, are designed to work to 51 or even 52MHz. These designs invariably sacrifice forward gain and pattern quality for wide SWR bandwidth.

Small Five-Element Yagi Home Depot Yagi Metric Yagis Log-Yagis Circularly Polarized Cubical Quads Circularly Polarized Crossed Yagis Circularly Polarized Loop.

When optimising a design over a narrow bandwidth, fewer elements are needed. As long as you have a certain minimum number, Yagi forward gain is determined by boom length, not element count. Elements added to the interior of this design won't increase its gain. (They may increase the bandwidth over which the pattern and SWR remain good, but this design adequately covers the low end of 6 meters.) Figure 1 - 3D plot - Peak 10.26 dBd @ 50.110MHz The free-space forward gain of this Yagi varies from 10.2 to 10.4dBd over 50.000 to 50.250MHz. These figures include conductivity losses of 0.08dB for 6061-T6 aluminium elements. When matched at 50.135MHz, SWR is less than 1.4 across the frequency range.

The worst-case back lobe is 20dB down at 50.000, 21dB at 50.100, and rises to 16 dB at 50.250MHz. This design was simultaneously optimised for maximum forward gain, minimum worst case back lobes, and adequate and impedance.

Conventional F/B was not optimised. This parameter takes the rear pattern into account at a single point. The tuning of Yagi elements depends not only on their length but also on diameter, diameter tapering, and mounting method. These factors affect element self-impedance and thus alter antenna response. Thinner elements, tapered elements, conductive mounting brackets, and through-the-boom mounting shorten effective element length. Design dimensions are given for insulated, untapered, 0.375' diameter elements, for insulated, untapered, 0.5' diameter elements, and for elements with Cushcraft A50-6S tapering and mounting. If you use different elements or mounting methods, you'll need to adjust element lengths for optimum performance.

This design has a special property which makes it easy to adjust element tuning experimentally. The azimuth pattern has three back lobes which are equal in amplitude only at 50.100 MHz. Since rear-lobe amplitude changes rapidly with frequency, you can easily verify that your antenna is correctly tuned. If the rear lobe is larger than the other two back lobes, the effective length of your elements is too long.

If smaller, your elements are too short. You can use this simple test to obtain correct electrical behaviour for any physical element mounted by any method. When adjusting parasitic-element lengths, make equal changes to all parasitics. The input impedance of this design is about 12.5 Ohms. You can use any matching method as long as you observe the fundamental rule of Yagi matching: Never alter parasitic-element lengths or spacings of an optimized design to get a good match.

Driven-element length has virtually no effect on gain or pattern, so you're free to adjust this dimension when matching. Don't after element spacing. Change parasitic-element lengths only to move the equal-back lobe frequency to 50.100 MHz.

Figure 2 - Polar Plots @ 50.088, 50.110, and 50.250MHz When I built this antenna in 1989, I gamma-matched it. However, I wouldn't do this with the knowledge I have today.

A gamma match can induce current on the shield of a coaxial feed line. It can also induce current in the boom unless the driven element is insulated. These stray currents can reduce forward gain and degrade the pattern. You may be lucky as I was and get away with gamma matching, but why take a chance?

Use a hairpin, T-match, or folded dipole and a good balun. The 12.5 Ohm input impedance transforms to a feed impedance of 50 Ohms for an equal diameter folded dipole. You can feed the folded dipole directly with 50 Ohm coax if you use a current type balun. You can make one by slipping ferrite beads over the coax or you can simply coil the coax into a few turns near the feed point. This design was developed in 1989 but was not published for some time.

A carefully constructed, untapered, insulated-element version of this design came out 220KHz low. (I had to DF cordless phones below the 6-meter band to find the equal-back lobe spot!) I thought that perhaps some obscure environmental factor was responsible for the discrepancy (like the conductivity or dielectric constant of my composition roof).

In typical ham fashion, I simply cut a quarter inch off each element tip and used the beam successfully. But the 220-KHz anomaly continued to bother me. It wasn't until I began to use the sophisticated Numerical Electromagnetics Code (NEC) that I finally understood what was going on. NEC predicted that the antenna would perform as originally measured. The MININEC-calibrated algorithm I used to optimise this design had a built-in frequency offset! I immediately recalibrated all of my antenna-design programs to NEC. I subsequently found references to the MININEC frequency offset in the professional literature.

If you optimise this Yagi for maximum forward gain without regard to pattern, impedance, bandwidth, construction tolerances, or reason, you can squeeze 0.2dB more out of the design. However, the back lobe degrades to just 11dB down and input impedance nose-dives below 5 Ohms. You say that you can match anything?

That you never leave 50.110? That you don't experience rear-signal QRM on 6 meters, and that you want all the gain you can possibly get? What about those damn power leaks that always seem to start up from every direction whenever the band opens? What about the 3CO DXpedition which shows up on 50.300 and gets chased off the island before you're done retweaking your match up on the tower? If you're greedy about Yagi forward gain, you'll live to regret it. Figure 3 - Polar Plot - 50.110.

0dB = 10.26dBd You can stack two of these Yagis for more gain. An H-plane stacking distance of 27 feet provides 3.1dB additional gain in free space. (Other stacking distances shift the equal-back lobe frequency away from 50.100MHz and require element readjustments However, unless the array is very high, you won't come close to free-space stacking gain in practice. The elevation patterns of Yagis at different heights don't combine favourably. For example, adding a second Yagi 27 feet below one at 50 feet improves gain less than 1.2 dB at elevation angles below 5 degrees. E-plane stacking is an attractive alternative. If you space the booms 29 feet horizontally, you'll get 3.0dB gain over a single Yagi regardless of height.

The 3-dB beam width will be 9 degrees, with deep nulls at 20 degrees and side lobes 9.4 dB down at 31 degrees. Before you go to the trouble of E-plane stacking, think carefully about the operational inconvenience of such a narrow main lobe.

The cross boom must be non-conducting near the Yagis. If you'll settle for an improvement of 2.6dB, the 8-element Yagi listed below is much more manageable than a side-by-side pair of 5-element designs.

To give you idea of how this Yagi compares with other designs, tables 1 and 2 show some NEC results at 50.110 MHz: Figure 4 - Polar Plot - 50.110MHz A50-5S, A50-6S, and 617-6B are wide-band Cushcraft designs. 6M2WL and 6M2.5WL are M2 Enterprises designs.

NBS-5 and NBS-6 are National Bureau of Standards designs empirically optimised for maximum forward gain. Five is the subject of this article, while Four, Six, Seven, and Eight are other computer optimised, narrow-band designs. Gain figure-of-merit is antenna gain minus maximum practical gain (maximum gain for the boom-length with reasonable input impedance and bandwidth, a definition which is vague but which can be evaluated mathematically as a function of boom length). As N6ND says, for a really good signal you need dBs in the air and dBs on the desk. This simple Yagi design will take care of airborne dBs. Desktop dBs are a matter between you, your licensing authority, and your spirit of adventure. Element Postitions and half lengths for Optimised 5-element Yagi (inches).

Position E1-#1 E1-#2 E1-#3 0.00 57.54 57.42 58.43 44.06 54.85 54.59 55.39 107.89 53.48 53.16 53.88 194.86 52.59 52.23 52.89 270.62 52.59 52.24 52.90 Element Positions and Half-Lengths For Optimized 5-Element Yagi El #1: 0.375' diameter, non-conductive mounting bracket EI #2: 0.5' diameter, non-conductive mounting bracket. El #3: Cushcraft A50-6S element mount 24' half-length of 0.75' diam., 0.625' diam. Tips, U-bolt mount Half-lengths are lengths measured from the centre of the boom to the element tip.

A half wave dipole on an 80m is about 130 feet or 40 meters long. Most of us humans think an element that long is difficult to build an rotate much less keep up in the air reliably even for a single winter. So what size would be worthy to try?

Something 75 to 100 feet might be manageable. So how do we shrink the length and maintain most of the performance and efficiency?

Having built linear loaded 80m Yagi’s since 1980, I know the concept works. I physically modeled the first dual driven, linear loaded 4 element Yagi at a frequency of 144 MHz. Scaling the element sizes was difficult but I was able to optimize spacing and linear loading location.

Once the model worked at 144 MHz, I then measured the resonance of each element individually and scaled the results by 38:1 and I had a full size starting point. It turned out to need very little tweaking. The first 80M4ll was built for Arnold Tamchin, (W2HCW).

Arnold wanted 20dB front and back and that is what he got. He wanted good bandwidth and the dual driven element and I gave him just that. Elements ended up at about 94 ft long and the boom was 76 Ft. Yes, did it play? Yes, enough to make Arnold gush! I put up the same thing on the West Coast and started working for Europeans reliably in the dx window at 3.790-3.800 SSB.

Now along comes “Computer Modeling”. Fortran based in the beginning and then in basic. Nec and mininec followed and Brian Beezley. K6STI produced YO (Yagi Optimizer) and AO (Antenna Optimizer), mininec based programs. Roy Lewellen (W7EL), followed with eznec and elnec, nec based programs.

This started a modeling frenzy. There was one problem however, nec based programs do not model linear loading accurately.

But many modelers using nec based modeling built linear loaded antennas and found they did not work?? Substituting coils for the linear loading did the job however. I was the proud owner of many versions of YO and AO.

Linear Loading in mininec based programs does work so many linear loaded antenna designs followed with good performance results. Some others built linear loaded antennas as well but for many reasons they did not work well so linear loading started to lose its credibility. All sorts of half baked theories filled the airwaves about current cancellation and whatever caused the loss of front to back and again. To most antenna designers coils seemed like the logical solution.

Mechanical design issues are important with both coil and linear loading designs. Efficiency is a serious issue when doing a coil design. A Few perceptive designers realized quickly that coil Q was extremely important, particularly at 40M and 80M! 160M is another story for another time. Here is an interesting side note. When coils are used in a dipole the coil Q is not much of a factor when related to efficiency. Poorly designed coils still work reasonably well.

But, when the dipole placed, physically and electrically, close to another similar element, the current in the element goes up dramatically and losses can completely kill the gain! If the modeling program either does not calculate final efficiency or the modeling ignores it, the low Q coil design looks great but it doesn’t work well in the field. Linear loading is much less critical to wire and tubing diameter losses but it still does show up once the antenna becomes a parasitic, directional structure. So to put this into perspective, extensive modeling with AOP (antenna optimizer, professional) shows that linear loading designs using decent diameter loading component work very well and are very efficient. Coil loading using wire size and fabrication techniques that maintain a Q of at least 300 works very well and are very efficient. The results of the multiple years of simultaneous, on the air testing shows no detectable difference in forward gain or front to back performance using linear loading on one antenna and coils with a Q of 500 on the other antenna. Modeling of each antenna showed virtually identical results meaning gains within.2 dB and F/B of 24 dB plus/ minus 2 dB.

So it comes down to personal choice based on your local weather and esthetics. The new concept in the coil fabrication that Matt Staal here at M2 came up with allow us to machine the coil from 1/8 wall aluminum tubing leaving a ½”solid tube section on each end of the coil. This makes for extremely low loss, high reliability coil to element connections, because the machining is accurate, the inductance value is the same from one coil to the next. It is one thing to wind a high Q coil on very good, low loss dielectrically only to see that beautiful coil compromised with small area, dissimilar metal connections to the element sections.

The physical covering and joining of the coil to the element is equally important to longevity and performance. M2 coil ends are CNC turned from 4” diameter aluminum billet and further CNC milling to remove excessive weight. A special 360 degree clamping connection insures maximum strength and reliability of the joints. Internally the coil floats on 4 thin strips of machined polyethylene, internally threaded, cover. This fabrication technique is a bit pricey but produces an almost indestructible inductor.