[NLRS] Yagi Design (Was: Club Cheap Yagi Build Day Advice Needed)

[Dr. Gerald N. Johnson]

On 11/19/2016 10:24 AM, James Duffey wrote:
> Jerry - We have strayed fairly far from the original topic, so I have
> changed the subject accordingly. That way people who are only
> interested in the WA5VJB antenna build can skip over it if not
> interested.
>
> I use MMana-Gal as well as YagiCad and 4NEC2 in my modeling of the
> WA5VJB antenna. For serious work, not that Bill’s WA5VJB project
> isn’t serious, I use a couple of different tools to confirm modeled
> results, generating new input files as I go. Testing without a good
> antenna range makes it difficult to confirm results, but if the SWR
> or directivity is way off that is usually a clue that there is a
> problem in the design or modeling, and if one can wait a year for the
> CSVHF conference to roll around, the antenna range there is useful. A
> number of years ago when I had access to a licensed version of CST, a
> professional (read expensive) 3D electromagnetic simulator and NEC4
> (controlled access only), I modeled the 3 element WA5VJB in those as
> well. Interestingly enough, the electrical properties of the antenna
> varied little with which model one used. I was aware of the closely
> spaced wires issue from W7EL’s work as well as conversations with
> Cebik at Dayton while he was still alive, so this good agreement was
> a bit of a surprise to me. However, when I modeled a dipole, a folded
> dipole, and Kent’s J shaped driven element (It is really more
> accurately described as a half a folded dipole) with the different
> models, they all showed the same gain and pattern. Only the input
> impedance and VSWR bandwidth were different, as one would expect.
> This makes sense as a dipole is a dipole, regardless of the physical
> form it takes. That gave me confidence that the WA5VJB antenna could
> be modeled well with any of those tools. This all makes sense in the
> context of how the Yagi works; the driven element serves to launch
> the electromagnetic wave in the antenna, and as long as the driven
> element geometry is efficient and balanced, then the particulars of
> the driven element are really only important as to matching to the
> feed line. With this in mind, the WA5VJB antennas can be modeled with
> simple dipoles or folded dipoles as the driven elements as far as
> things like element diameter correction, boom correction, and
> frequency scaling go. One just needs to account for the driven
> element impedance when looking at things like VSWR and matching or
> model the VJB driven element exact.

I model a yagi like the M2 or K1FO by taking the elements and running 
the G3SEK basic dos program (element.bas) to remove the boom correction 
and I model without a boom. I haven't found a method of moments program 
that handles intersections of different diameter wires or intersections 
not at 90.0000 degrees well. The fundamentals are that the currents are 
presumed to be at zero diameter at the center of the wire and that the 
coupling is from the center of the segments nearest the intersection. 
When at 90 degrees the coupling is figured as zero because the fields 
are at right angles. Unfortunately the current distribution is not 
anywhere near like that presumption. Especially in close spaced conductors.

I invented an antenna I called a Cat's Cradle involving angled 1.5 wave 
radiators gathered like a gang of small rhombics. Modeling in EZNEC the 
gain and patterns varied drastically with slight changes of inputs, as 
much as over 3 dB change in gain for a tiny change. I whipped one 
together a day before CSVHF and took it and it displayed the gain of the 
lowest modeling results, not the peak. It also as a single array worked 
better with the boom vertical than pointed at the 1296 signal source, 
much like a diamond array. In my modeling stacking 4 cleaned up the 
strong elevation lobes. But I only built one.

That experience and many claims for great front to side ratios enhanced 
by flat loop driven elements or angled driven elements that were 
guaranteed to couple current to the boom caused me to publish
http://www.geraldj.networkiowa.com/papers/2013/FinePoints.pdf in both 
CSVHF and MUD 2013.
>
> I have never heard the pejorative Crumcraft used when referring to
> CushCraft before. I have heard of them referred to as CushCrap
> though. They were more crippled by their marketing department than
> the performance of their antennas, although now that MFJ owns them,
> that may have changed. The CushCraft antennas based on NBS Tech Notes
> 688 perform as one would expect from the NBS data, which is not too
> surprising as those antennas were designed to be reproducible if one
> followed the directions in the Tech Note for designing and building
> the antennas.

That is my invention. Their NBS copies did work as the originals but 
they claimed several more dB claim, like adding ground reflection gain 
or link gain with the same antennas on both ends of a link. Maybe their 
reference was a rubber duck antenna inside a fruit juice can. Their 
outrageous gain claims caused a permanent QST policy that antenna gain 
claims are not allowed in QST advertisements.

Their 11 element 2m and 432 yagis with all but the front director the 
same length did have some directivity but their poor quality (too wide 
spaced) gamma match feed took several DB out of the gain. Most yagi 
gurus don't like the gamma match feed accusing it of killing the 
symmetry of the yagi pattern and that could probably be applied to the J 
feed of Kent's antennas. But on a short yagi the pattern is going to be 
wide enough that any asymmetry is going to be virtually impossible to 
detect.

I took a 432 crumcraft with my own very close spaced gamma match to a 
CSVHF about 1967 and it didn't give the claimed gain but was more than 3 
dB better than the original measured at CSVHF. The gang laughed out loud 
when they recognized it before it was measured.
>
> The K1FO designs were optimized not only for gain, but also for low
> side lobes and reasonably wide bandwidth, and he was the first to
> effectively optimize all three of those parameters. They were a big
> improvement over the NBS designs in that they emphasized important
> antenna properties in addition to gain.

The were based on DL6WU designs and rarely gained as much as a whole dB 
in forward gain.
>
> The NBS antennas lived on through the 90s not as marketable antennas,
> but often as starting points for the genetic algorithms that were
> becoming available then to optimize antenna performance. I think the
> generation of CushCraft antennas after the NBS clones, such as the
> 13B2, were done this way, and they were and are good antennas for the
> boom length. There are better antennas available now, but the 13B2
> speaks to the advance in computing power applied to antenna design
> from the late 70s to the early 90s.
>
> YagiCad has no relation to Yagi Optimizer, it is a completely
> different program; essentially a Yagi specific front end interface to
> a NEC computational engine. Elements are entered in a spread sheet by
> position on the boom and full element lengths are used. It is much
> improved over generating a bare NEC card deck. You should try it out
> if you have not. It is a very useful piece of software. It has its
> limitations, as do most modeling tools, but it gets one pretty far up
> the design curve without a lot of problems. It has an optimizer and
> does scaling, both for frequency and element diameter and you can
> chose several techniques for doing this.  It has a genetic optimizer
> and a calculator for various types of matches. If you want to do
> something outside of its limitations, it generates .NEC input files
> which can be used in any NEC or miniNEC based tool; barebones NEC,
> MMana-Gal, EZNec, CocoaNEC, or 4NEC2; and it can generate 4NEC2 input
> files so you can use the extended features of 4NEC2 in your modeling.
> As with all modeling tools one needs to study the results of the
> model carefully and make sure that they make sense from a physics and
> physical point. But that is the case in any modeling. Try it, I think
> you will find it useful.
>
> I think that there is merit to optimizing G/T, even for terrestrial
> use, although I realize that is not a universally held belief. It can
> make a big difference if your neighbor’s plasma TV is on a -10dB side
> lobe or on a -30dB side lobe. For the same boom length, there is a dB
> or more in SNR to be gained with the same length antenna by choosing
> an antenna with a clean design. That is a lot to disregard without
> some thought. I realize that you live in the country, so that may be
> a lesser consideration for you, but I think that relying on the
> station on the other end to have an antenna with less than optimum
> properties to work me is asking the station on the other end to give
> up a lot just for my advantage. I do agree that having 2 or more
> short antennas stacked vertically is a much better setup for
> contesting than a single long boom antenna. And much better for the
> rotor.

My contest Q rate to the cities and to Chicago has gone down with the 
adoption of the better G/T antennas, and then I moved and don't have 
antennas up on a tower which hurts a lot too. Some contests I've not 
even worked my own grid but I've won certificates with 2 digit scores 
like the SOLP class in the whole Midwest Divisioin from home 2015 UHF 
contest with 48 points. Definitely a sign of sparce activity.
>
> Thanks for pointing to me to your paper on stacking and the modeled
> performance of various antennas. It was very interesting. I don’t see
> the modeling of the 12 element M2 antenna you referred to in your
> earlier post in that article though; did I miss something obvious?

I didn't model the 12 element, just the 9 on a boom longer that K1FO 
with slightly lower gain.

> You may want to revisit your modeling of the M2 9 element antenna.
> The gain you modeled is over a dB lower than the gain I modeled for
> that antenna when I was doing analysis for a friends stack that
> contains a 2M9SSB. It is also about that much lower than the gain for
> that antenna that VE7BQH quotes in his table of modeled Yagi data
> which he generates from several modeling programs and which is
> generally considered an accurate representation of the performance of
> existing antennas. I can dig out and send you my .NEC file for that
> antenna to compare with your input file and to check your model
> output. If you want to send me your input file, I would like to
> review that against mine as well to make sure that I haven’t made any
> mistakes. The modeling should be consistent, and when it isn’t it
> helps one’s future modeling efforts to find the cause. The modeled
> gain for the 9 element K1FO variant looks about where it should be
> though, so it looks like your Yagi modeling process with MMana-Gal is
> fine.
>
> Keep in touch. - Duffey KK6MC

Here is the Mmana-Gal 2m9ssb.maa file that I used for my conclusions. No 
boom.

> 2m9ssb
> *
> 144.2
> ***Wires***
> 9
> 0.250825,	-0.494284,	0.0,	0.250825,	0.494284,	0.0,	8.000e-04,	50
> 0.0127,	-0.514121,	0.0,	0.0127,	0.514121,	0.0,	8.000e-04,	50
> 0.576263,	-0.464434,	0.0,	0.576263,	0.464434,	0.0,	8.000e-04,	50
> 0.873125,	-0.461632,	0.0,	0.873125,	0.461632,	0.0,	8.000e-04,	50
> 1.417637,	-0.463329,	0.0,	1.417637,	0.463329,	0.0,	8.000e-04,	50
> 2.124075,	-0.456979,	0.0,	2.124075,	0.456979,	0.0,	8.000e-04,	50
> 2.90195,	-0.450629,	0.0,	2.90195,	0.450629,	0.0,	8.000e-04,	50
> 3.762375,	-0.447624,	0.0,	3.76375,	0.447624,	0.0,	8.000e-04,	50
> 4.4323,	-0.450799,	0.0,	4.4323,	0.450799,	0.0,	8.000e-04,	50
> ***Source***
> 1,	1
> 25,	0.0,	1.0
> ***Load***
> 0,	1
> ***Segmentation***
> 800,	80,	2.0,	1
> ***G/H/M/R/AzEl/X***
> 0,	0.0,	3,	21.0,	120,	60,	0.0
> ###Comment###
> Mod by Gerald N. Johnson, K0CQ 1/23/2011 6:19:23 PM
> Created by Gerald N. Johnson, K0CQ 1/23/2011 5:08:08 PM

In 1983 at CSVHF in Lenaxa KS, W0WL (silent key according to a recent 
QST) a long time Collins Radio employee with a ham radio reputation for 
doing extremely beautiful construction work had a NBS 432 yagi made with 
a square aluminum boom and aluminum elements welded in place. Looked 
beautiful, but on the antenna range was down 5 dB from the NBS data. 
Turned out he ignored boom effects and element diameter effects and used 
the lengths for wooden boom and 3/16" elements with a 1" square aluminum 
boom and 3/8" diameter elements (IIRC) from an ARRL Handbook. I had my 
own version of a NBS standard gain antenna for 432 but it was too heavy 
to get up on the pole and near the ground it had more than 4 dB ground 
gain over the theory. Two half waves in front of a 1 wave square 
reflector or was that a 2 wave reflector? My 7 dBi antenna showed a 
stronger signal than Warren's where there should have been about 5 dB 
the other way. That really pointed out the importance of boom effect and 
element diameters. Its probably also true that element diameter effects 
the coupling from element to element but NEC variations ignore that.
>
>
73, Jerry, K0CQ