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Director Extension

Message to Holl_ands et al:

Well, after all these years, I've just managed to discover this thread. A lot of great info here and all very interesting.

A week ago the power company came by and told me the tree in front of my house, holding my modified Y10-7-13, about 85' up, has got to come down. Aaaarrrrggghhh.... The tree does have a split trunk, and they're saying within some reasonable time frame it's going to come down on its own. Since one trunk would pretty obviously land right on top of my house, I'm taking the arborist's word for it.

The main reason I paid somebody to put it up there is EMI. The power line serving my street runs almost parallel to the line of sight. When the antenna was originally mounted above the rear peak of the house, at about the same altitude as the lines but maybe 80' or so away from them, it often resulted in various degrees of pixilation; sometimes bad enough to make the signal(s) unusable.

So I'm faced with the options of either (a) convincing my wife we should put up an 85' tower, or (b) returning to the original mounting location, and the probability of succeeding with (a) is infinitesimally small ...

That said, it occurs to me that a few steps to improve directivity might help; narrowing the pattern in both the vertical and horizontal planes. So I'm considering two things. [1] implementing that 5 director extension I posted near the bottom of the above link, and [2] changing the planar reflector to either a corner or trough reflector.

On the subject of [1], I'm second guessing myself now on the spacings I originally posted for the extension. I arrived at them empirically, using my spectrum analyzer and its tracking generator, setting the span across the Hi-VHF band, adding each director one at time adjusting position for max response, and then iterating. But: one thing I could not eliminate from the surrounding environment was the ground; i.e., no good elevated platform for getting away from ground reflections.

So, I'm wondering what positions and lengths you might recommend? On that note, and regarding discussions here about Ch 13 drop off, in my own tinkering I found that shortening just a few of the front directors helped a bit with this, and using a slightly longer reflector helped at the low end. I can guess that results in some mid-band loss. But for me 7 and 13 are both in use, and I opted for the improvements. Just FWIW...

Regarding [2], I've been reviewing the material in Johnson & Jasik's "Antenna Engineering Handook", the "AARL Antenna Handbook", and everything I can find on Google. There are some consistencies, and some inconsistences. But there does seem to be some agreement about length of the panels recommend for the basic corner reflector, mainly from 1 to 2 wavelengths, and physically not so practical.

I'm going to implement a hinged corner to experiment with, but I wonder what your thoughts might be on the merit of implementing something just long enough to get forward of the 1st driven element (DE closest to front)? Maybe about 3/4 wavelength (45 inches or so)?

In case you're interested there is one video of the EMI here, and in this one, I toggle the trigger mode back and forth between Free Run (asynchronous) and Line modes. In Line mode the "wandering" of the noise from left to right ceases (synchronizes with the start of trace).
 

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I'm happy to ReRun one (or more) of my YA-1713 Models [Hmmm, must pick one....so many to chose from]. I can ReRun with 5 Added Directors per your provided measurements. For comparison, I ALSO want to Run the one you are currently using with 3 Added Directors if you can provide Dimensions....or confirm that it matches one of the one's I've already uploaded to my imageevent Website. I would also appreciate if you could MEASURE YOUR YA-1713 just to make sure that it's the same as mine, whenever it becomes available again. I also intend to investigate how much those 7 Reflector Rods are helping....maybe only 3 RR's are needed, depending on whether you "NEED" the highest Forward Gain or the best F/B & F/R Ratios???

BTW: Back when Mt Wilson (L.A.) was still broadcasting Analog NTSC on Ch7/9/11/13, at my son's old house 70-mi away from the Transmitters, I inserted a considerable amount of Attenuation on the output of the YA-1713. I measured how much attenuation it took before the Video and Audio Carriers were lost on each Channel. I saw NO DIFFERENCE on Ch13 [or Ch7] compared to the others...which means that the Ch13 Roll-Off shown in the 4nec2 Models was NOT REAL. I have seen similar MODEL PROBLEMS in other Log-Yagi type antennas, such as the RCA ANT751 (which is why I didn't post my Model Results other than some Gain Summaries):
http://imageevent.com/holl_ands/logyagi/wgya1713

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I believe that your BEST approach would be to use a PAIR of Vertically Stacked Antennas [Frankenstein four Stellar Labs Yagis, once I complete the 4nec2 Analysis Runs???]. This will generate NULLS in the Elevation Pattern above and BELOW the Beam. A "TILTER ADAPTER" is typically used to adjust how much UP ANGLE is used, depending on WHAT ELEVATION ANGLE you need that NULL to be to best cancel the Ground Bounce path. I don't have some good Vertically Stacked Hi-VHF Antenna examples to show you, but the fol. UHF examples illustrate the point, since a RESCALED (UHF to Hi-VHF) Antenna would perform exactly the same:
http://www.atechfabricatiohttp://ww...mn.com/products/antenna_mounting_brackets.htm [Antenna Tilters]
UHF V-Stack 8-El FD-Yagi w. 2RR Ea - OPT
UHF Vertical Stacked A-D 91XG

Two, shorter [say 1.0X Normal Size] Antennas can provide the SAME Raw Gain as a Single, say very long Antenna....and indeed EACH could be extended to say 1.5X Normal Size vs 2.0X in a Single Antenna, more than overcoming the 0.5 dB Internal Coupler Loss. With a "nominal" Combiner Loss of 0.5 dB (higher on upper UHF Channels), two matched Antennas will typically provide 2.5 dB higher Raw Gain than just one.

BUT WAIT THERE'S MORE....because Multipath Fading affects each Antenna DIFFERENTLY (incl. the uneven Freq Response you see will likely be DIFFERENT, yielding a smoother Combined Response), when one of the Antennas is experiencing a Deep Fade, it is unlikely that the OTHER Antenna is ALSO experiencing a Deep Fade. Since individual Glitches are very INFREQUENT compared to the very high speed data rate, it is fairly RARE for BOTH Antennas to experience a Deep Fade at the same time. This SPACE DIVERSITY Combining Gain (typ. 10 dB) is in addition to the Combiner Gain. Shorter Antennas also have numerous other Physical Advantages, incl. resistance to the Wind and less torque on a Rotator.

It sounds like your Antennas are currently mounted so that they "Look" directly thru the Powerlines, maximizing the Impulse Noise Pickup [which would be much worse on Hi-VHF than UHF]. Is it possible to mount the Antennas LOWER, so that they "Look" BELOW the Powerlines, bearing in mind the Elevation Beamwidth of each Antenna????

Could you send me a PM with your LAT/LONG (to as accurate a location as you are comfortable with) so I can look at the surrounding Terrain???
 

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RE: Director Extension

PM sent.

Yes, at 14-15' above the house, the power lines will be at about the same altitude as the antenna, and about 38' off the line of sight.

Your suggestion of the dual v-stack is interesting; I completely agree on the merits with respect to multipath, and have pondered the option. Multipath used to be a very popular (late evening in the lab) topic when I was in the Transmission Systems Engineering department at Bell Laboratories in New Jersey; it included radio, copper, and fiber groups. Somewhere else I've commented on the potential merits of 8-bay designs over yagi's for UHF in this regard!

Trouble is available vertical space on the mast. Without going to something heavier duty (mast wise) I can only get about 14' above the peak, and I need to get a (UHF) CM4228 up there too. Even minimizing the separation of the VHF rigs to a wavelength would bring me down to about 9 ' from the peak (for the bottom unit), and then leaving a few feet for separation to the UHF element brings its elevation down into an interesting (read: "troublesome") reflection zone off the metal roofing. I.e., there are a nulls that occur because of out of phase reflections from the roughly 40 degree roof pitch.

But, consistent with your suggestion, and given the power lines will now be to the side, I wonder what your assessment of a horizontally mounted pair would be? I.e., narrowing the horizontal vs vertical beam width?

Regardless, the mounting complexities of either pairing have me thinking about options for improving options for forward directivity of the single antenna, including the extension and corner reflector.

Studying Johnson & Jarik's illustrations on pp. 17-3 thru 17-5 ("Antenna Engineering Handbook), implies a 60 degree corner reflector would offer some side lobe response reduction over a planar or single reflector. At this lower altitude than the tree, I also need every bit of (forward) gain I can find.

The measurements of my Y10-7-13 pretty much agree with those of tripelo's at his post here, with the exceptions that I get a D3 spacing of about 10.78 (10 3/4 plus about 1/32), a D5 spacing of 17.75, and a D6 spacing of 18.9375 (18 15/16). There differences are all within 1/16 of an inch; maybe that's within manufacturing tolerances, or maybe not.

I'm off to browsing your ImageEvent Y-10-7-13 work . . .

Thanks again!
 

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ERRATA: I messed up the numbers in my above post....should be A-C Y10-7-13 Model instead of W-G YA-1713:
Log-Yagi & Dual-Driven Antennas - ImageEvent
Note that this includes the Y10-7-13 with ADDITION of 2 Reflector Rods and 3 Directors, "repurposed" from MCM Stellar Labs 30-2475 8-El Yagi ("AS IS" with NO CHANGES....NOT Re-Optimized Dimensions).

Q1: Is this the 3 Added Directors version that you are currently using???

In your drawing of Y10-7-13 with 5 Additional Directors, I see SIX Vertical Rods where the Third from the Right is only shown in outline (Phantom?). In the Y10-7-10 model (per tupelo/re_nelson measurements), the most FORWARD Director on the unmodified Yagi is 117.44-in from the Reflector.

Q2: Is the "Phantom" a Position that you tried and decided to eliminate in the final version....Or is the Director on the Far Left the most Forward Director in the original Yagi???

Q3: What is the Separation between THAT Director and the First Director in the Added Boom Section???

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Whether Vertically or Horizontally Stacked, resultant Gain in the Beam will be about the SAME. Obviously, Vertical Stack has better rejection of Ground Bounce (if that is indeed a source of Multipath for the assumed two-path Angles of Arrival and local Terrain smoothness). And a Horizontal Stack provides a narrower Beam in Azimuth, at the expense of a wider Beam in Elevation. From what I've read, relative performance varies from situation to situation....you'll just have to try one or the other....or both. Either way it SHOULD be an improvement....hopefully....as always YMMV.... [WHAT??? You expected definitive ANSWERS???? Sorry....]

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FYI: In UHF Band, a 1/4-in change in Dimensions barely moves the decimal number in Gain and SWR....so in Hi-VHF Band, a 1/2-in change won't be measurable.....and it would take a much larger "error" to actually be NOTICED in everyday watching....

First of all, Hi-VHF Antennas have much smoother Sidelobe Response than UHF Antennas. Thus far, my Optimization Runs for Corner Reflector Yagis have concentrated on several alternatives for a specific NARROWBAND UHF application, so I don't have any APPLES-to-APPLES comparisons....but I doubt that Corner Reflector Yagi's have significantly "better" Sidelobes than conventional Yagi's. Nonetheless, I have drawn the fol. conclusions from what I've seen so far:

a) Corner Reflectors act "sort-of" like Parabolic Reflectors and hence work BEST with SHORT Yagi's that (like a Parabolic) provide the most Gain Enhancement for those Elements near the "Focus Point"....indeed you will see that the SHORTER 15-El FD-Yagi with 14RR Corner had HIGHER Gain than it's 18-El 14RR counterpart (with or w/o Length Constraint):
http://imageevent.com/holl_ands/yagis
These particular runs are OPTIMIZED, where ALL Lengths and Placements are determined by nikiml's Python Scripts.

b) Adding more and more Reflector Rods eventually provides Diminishing Returns....indeed 18-El 10RR had MORE Gain than 18-El 14RR with LENGTH CONSTRAINT....and MATCHED it when allowed to grow to Excessive Length. Also note that as you allow more and more RR's (e.g. 20RRs), they do NOT grow much more, overlapping ONLY the first THIRD of the Antenna...they simply end up being closer and closer together, which primarily improves F/B and F/R Ratios.

c) The best use of METAL is to add more DIRECTORS and hence LENGTH (Gain is proportional to LENGTH), rather than more Reflector Rods:
http://www.g3ubx.com/aerials/length.vs.gain.html
http://www.dxmaps.com/ve7bqh.html
The V37BHQ article plots G/T rather than simply Gain, where T is the equivalent System Temperature (related to Noise Figure) for JUST the Antenna itself [and MAY have left off some Interconnect Harnesses???], which facilitates the intended EME (Earth-Moon-Earth) Antenna Selection process by INCLUDING the ADDITIONAL SKY NOISE that would be picked up by the SIDELOBES. HOWEVER, when the Antenna is pointed more or less at the Horizon, Tsky jumps up to whatever the GROUND Temperature may be at the Horizon, making the Chart less useful....whatever, it's still a good Chart...and note that you may see a few Reflector Rods in a Flat Array, but you will NOT see any Corner Reflector Yagi's in any EME Arrays....see fol. for more info:
http://owenduffy.net/blog/?p=1316 [Partial explanation of V37BQH's Q/T Plots.]
http://www.qsl.net/yu1aw/Misc/vhfnoisetemp.pdf [Better explanation of Q/T which INCLUDES SKY NOISE pickup.]
 

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I'll respond to all questions shortly. In the meantime, I should emphasize the primary goal here is to minimize both horizontal and vertical side lobe response to a source of EMI which is 90 degrees off the forward horizontal axis, and maybe 20 degrees below it. Intuitively, a corner reflector long enough to extend just forward of both DE's of the Y10-7-13 should offer some reduction in response to EMI being generated immediately to the left of and just below the antenna.

I am mostly wondering if you concur on this aspect.
 

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Q1: Is this the 3 Added Directors version that you are currently using???
No, it is the same as the 5 director version minus the two rightmost directors.

Q2: Is the "Phantom" a Position that you tried and decided to eliminate in the final version....Or is the Director on the Far Left the most Forward Director in the original Yagi???
Dang. My bad for not providing more a precise description. First, there is no "phantom" - for some reason the published graphic simply reduced the line width of that element. Second, the illustration meant to convey that the extension is based on an extension boom of outside width slightly less than the inside width of the stock boom, such that it is inserted into the end of the stock boom by 6". Thus the leftmost director of that illustration is the Nth (7th) director of the stock model, and the 5 directors to the right represent the added elements. [What that "5/8" dimension of the illustration intended to convey I honestly can't recall now.]

FYI: I'm aware the dimensions don't match anything I've ever gotten from various yagi calculators, nor those of your work. Again, I arrived at these empirically, by tuning for max gain, one director at a time. As I mentioned, I'm second guessing my spacings now with respect to the potential for the influence of ground reflections in my hacking arena, although I confirmed the overall improvements for both horizontal and vertical polarizations. This time I'll be able to repeat the empirical exercise at better altitude.

Q3: What is the Separation between THAT Director and the First Director in the Added Boom Section???
I hope the Q2 discussion above answers this as well, but to be clear, the separation between the Nth stock director, and the 1st added director is 16" (the leftmost spacing of the illustration).

Your additional insights much appreciated,
t
 

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I finally modified the Y10-7-13's 4nec2 Model with 5 additional Directors and 4 Reflector Rods....and an Ultimate Optimization is Running....cuz your "as-built" was looking very shaky on BOTH Ch12 and Ch13.....

One final Question: Although I don't think I saw some explicit Dimensions, from the Diagram it appears that the Lengths of the Added Directors are the SAME as the Length of the most forward Director on the Original Y10-7-13. Is this assumption correct????
 

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16, 18, & 20-ELEMENT Hi-VHF FD-YAGI's (Only ONE Reflector Rod):

FYI: I uploaded 4nec2 Analyses for three more LONG Yagi's for the Hi-VHF Band, in addition to the 22-El FD-Yagi previously uploaded:
Yagi Antennas - ImageEvent
These represent the BEST of several runs for EACH version as I vary the relative "importance" of SWR vs Gain. I'm seeing some variation between runs wrt Gain (+/- 0.5 dB) and Boom Length (+/- 30-in)....so over time I MIGHT add some more runs. Since there isn't a smooth progression in performance as more Directors are added, I suspect I haven't yet found THE Absolute BEST for each type.

I have also begun investigating ADDING 2 and 4 Reflector Rods [in an aligned Vertical Stack] to the 16-El FD-Yagi...which again will take several runs EACH. And after that, I'll start investigating ADDING different Corner Reflectors, similar to the work I did earlier for Narrow Band UHF FD-Yagi's.....

PS: I just ordered the parts to upgrade my old 3-Core AMD PC to a 12-HyperThread i7-5820K, so it will be identical to my other OverClocked Desktop....which [depending on how much Free Processor Time is available] can actually run TWO Optimizations at the same time, as I also experimented with on my 8-HyperThreaded Laptop, running one under Python3.3 and the other under a separate Python3.5 Installation....if only I can wrap my mind around what I THINK I'm trying to do with up to SIX Parallel Optimization Runs....
 

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holl_ands you are doing great work. With the worry of a repack down into VHF, these will be very useful. I'm pondering far off VHF, so I'll be thinking of an HVH to go along with your research. Best of luck with the Analyses and upgrades.
 

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holl_ands said:
One final Question: Although I don't think I saw some explicit Dimensions, from the Diagram it appears that the Lengths of the Added Directors are the SAME as the Length of the most forward Director on the Original Y10-7-13. Is this assumption correct????
Rats. Can't believe I left that out. Until they cut my tree down I won't be able to answer precisely; I'll measure it at that time.

But my recollection is that I shortened the 7th (last) director of the stock model by a modest amount, like about 1/2 inch, and matched the added directors to that.
 

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holl_ands said:
I finally modified the Y10-7-13's 4nec2 Model with 5 additional Directors and 4 Reflector Rods....and an Ultimate Optimization is Running....cuz your "as-built" was looking very shaky on BOTH Ch12 and Ch13.....
Went browsing your yagi pages but didn't come across this work. Have you published it yet?

I can believe it looks shaky. But the analyzer trace screen captures are what they are for MyY10-7-13, I just have difficulty explaining the spacings. That's one of the reasons I compared at two separate locations. Clearly the results have differences, but the trends are similar for both locations and were emphasized at the high end . . . go figure.

Remember, I arrived at those spacings simply through trial and error. I made up a 15' long length of 1/4" thick by 1" wide wooden molding, strapped a director to one end, and laid the molding along the top of the boom, with that (1st director to be added) an arbitrary 1 foot or so forward of the existing director at front, and with the other end of the molding extending out the rear of the antenna - beyond the reflector. Then I stood several feet behind the reflector, and simply slid the added director forward and backward, "tuning" for max signal level on the spectrum analyzer. As each optimal spacing was found I fixed the director in that position, and repeated the process for the next director. Then I went back and started over at the 1st (added) director leaving all other new ones in place, to see if the "optimal" position had been affected. My recollection is that I made only very minor adjustments to the spacings on that pass.
 

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I was waiting for your answer re Director Lengths before I posted EVAL Results for "As-Built" AND for the OPTIMIZATION Run to complete for comparison to what COULD be achieved if Element Locations are changed and Lengths possibly Shortened [I'm using Length of Original Front Director as the Upper Limit...and 1/2-in difference is negligible]....soonish....
 

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What do I have to do to be able to attach a couple of .jpg files? I'd like to share a couple pictures of the corner reflector I'm implementing and get your feedback . . .
 

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rabbit73: Thanks for that. I'm happy to contribute, and will, was just looking for something convenient. I'll post to my hacks website for now, 'cuz that's where any/all results will wind up anyway.

holl_ands: I've posted preliminary drawings of a positioning side view and a side view mechanical detail for the corner reflector I'm entertaining.

Again, as mentioned in post #106, the main goal is improving front/side and front/bottom ratios (immunity to local power line EMI). In the process I'd like to implement your recommendation on the 5 director extension. I'll capture that result, then I'd like to go back and tune directors manually per the process I related earlier and see how they compare.

Any thoughts on the reflector welcome - from anyone.
 

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RE: Corner Reflector

It occurs to me I should mention a few things regarding goals and construction. The single dominating goal is to improve immunity to EMI from power lines located below and to one side of the antenna location. My war with the power company is not going well. The resulting sub-goals are to reduce sensitivity (gain) to the side and bottom. I expect the side gain to be reduced by the inherent properties of the corner reflector, and the gain from the bottom to be reduced through construction choices and positioning steps described below.

Regarding construction, the upper and lower halves of the reflector will be hinged at the vertex so I can experiment with the corner angle. I've illustrated 45, 60 and 90 degree configurations on the positions drawing. I've drawn the vertices at a common spacing to the rear of the (arbitrary) center of the two Driven Elements DE1, and DE2, just as a rough locator. The spacing should be close to 1/2 wave for all cases, but slightly greater for a 45 degree corner and slightly less for 90.

I intend to initially fit a rear boom extension of about 2 1/2 feet, and prepare vertical support (not shown) in such a way as to be able to slide the reflector along the boom. In this way I expect to find optimal spacing distance for various angles. Once determined I'll cut off any unneeded length.

I chose 36" rod lengths because of Johnson & Jasik's recommendation of 0.6λ. At the mid-band frequency of 195MHz, and wavelength of 60.5", the result is about 36". Also, this length is conveniently available pre-cut from a variety of sources. I'm ignoring conductor velocity.

I chose a panel length of 40" because I intend to point the boom up from the ground by 17 degrees. With the full assembly rotated to this angle the 40" length results in the lower reflector panel extending just forward of both driven elements when viewed from directly below the rotated assembly. This creates a plane in between the driven elements and the offending (EMI) noise source which is below the antenna. I'm thinking this might improve the front/bottom (and front/top) ratio, and thus help the signal to EMI noise ratio.

I'm rotating the assembly upward because the power lines do run somewhat along the forward line of sight, and there is therefore a an on-axis EMI noise contribution in addition to those from side and bottom. But through field experiment I can drop that noise contribution noticeably by elevating the antenna upwards from 0 degrees. I arrived at 17 degrees by noting this is the point where signal level just begins to fall off (maybe by about 1 dB). I.e., the noise level drops continuously going from 0 to 17 degrees and a bit beyond, but going further than 17 degrees causes the signal to begin dropping off also.

One aspect that makes me want to experiment with reflector spacing is the dual driven element design of the Y10-7-13. As I understand, the main benefit of using dual DE's is extending the bandwidth. But with regards to reflector corner spacing the question is at what distance, exactly, should it be spaced with respect to the two separate driven elements? I.e., do the two DE's contribute to overall gain equally across the band, or is each a dominant contributor at a different end of the spectrum? I am expecting the later, and to be able to emphasize at either end as needed by adjusting the spacing.

Any/all insights welcome.
 

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I have an issue with power lines as well so I've been following the discussion. Horizontal tacking can be also be used to improve horizontal directivity and create nulls to the side. Vertical stacking improves vertical directivity. Any stacking will improve overall directivity. Creating nulls to other directions, such as below and sideways might require a more creative approach or a 4 antenna array.

With regard to dual driven elements, it seems to me that this could also be used to improve gain and directivity on a single channel. Tuning the size and spacing of the driven elements for a single channel should do this, at the expanse of other channels. Not sure how this would compare to adding directors and reflectors though.
 

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Any stacking will improve overall directivity.
Yeah, I wish I had enough mast length to try a vertical stack; it would be so much easier. I had a pair of 91XG's (UHF) up horizontally for a while, but we get 50++ MPH wind gusts here and ultimately I woke up one morning to a mess. It would be even more physically challenging at VHF sizes.

With regard to dual driven elements, it seems to me that this could also be used to improve gain and directivity on a single channel.
I suspect you're right. Following the old physics class wisdom of "take it to the limits" (to get an intuitive insight into the effects of maximizing or minimizing a parameter), I'd say if you continue to decrease the distance between the two DE's, collapsing them to a separation of 0" and thus a single DE, you then wind up with a standard Yagi?

What I really wish for, not to let this get off topic, is a magic bullet I can fire at the power company . . . :devil
 
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