Scale holl_ands H2 (10"x15") 2-Bay Bowtie - Canadian TV, Computing and Home Theatre Forums

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post #1 of 14 (permalink) Old 2018-12-08, 06:20 PM Thread Starter
 
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Scale holl_ands H2 (10"x15") 2-Bay Bowtie

My reception needs dictate a high gain antenna to receive channel 22, everything else can be received with an indoor antenna, so everything I put up outside brings in my channel 8 and 20. Even a single bay hourglass with no reflector. From my experience, I estimate I'll need 16 to 17 dBi gain for consistent reception on channel 22. Currently I'm using a narrow band Hoverman from jedsoft.org scaled up in size for channel 22, but I was not careful with wire size and reflector element size, so I probably did not realize the estimated 16dBi+ gain of the design. This antenna works OK for me, but not quite as well as the UHF section from a CM-3020 that I've mentioned elsewhere on this forum. Specs from Channel Master shows about 14dBi gain on channels in the lower 20's for the 3020.

Thus my interest in what holl_ands himself describes as having performance "significantly better than ANY other 2-Bay Bowtie." Only thing is it's peak gain looks to be about channel 56-58 (maybe 731?MHz). So my plan is to scale all dimensions up by a factor of 1.4 to try and get the maximum gain closer to channel 22, plus double the number of bays to four instead of two.

What I'm hoping to attain is a 4-bay bowtie antenna with a gain of about 17dBi @ 521MHz. Do you guys agree that I'm on the right tract? Or do you have a better suggestion?
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post #2 of 14 (permalink) Old 2018-12-08, 08:22 PM
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H2 and FF4 are an Optimized UHF BROADBAND Antennas. I'll take a look at some alternates and do a Re-Optimization for a Ch22 NARROWBAND 4-Bay Antenna which should have even higher Max Gain than FF4. I'll presume use of the FF4's Double Angle Reflector [or do you prefer Flat Screen Grid???], which should ALSO be larger....so stand-by for a few days....

Did you have a preference for Element Size????

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands

Last edited by holl_ands; 2018-12-08 at 08:42 PM.
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post #3 of 14 (permalink) Old 2018-12-09, 09:48 AM Thread Starter
 
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Thanks for the help holl_ands. I think I prefer Flat Screen Grid. As I understand (could be wrong of course), a flat grid and no angle on the elements is better for narrow band. But I'm looking for max gain here, so if that means using DAR, then let's go for it!

As for element size...either 10 or 8 gauge wire is available.

Edit: On second thought, I have a bunch of 3/8" tubing left over from some old FM & VHF antenna that could be used for the bowtie elements. That might make for a more sturdy construction. Would probably still use wire for the phase lines though, and standard 1"x2" grid small animal fencing for the reflector screen either way.

Last edited by Neil L; 2018-12-09 at 12:00 PM.
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post #4 of 14 (permalink) Old 2018-12-12, 03:30 AM
 
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I beleive 2-bay array peak is about 13 dBi, as single bowtie peak gain is ~10 dBi
https://ypylypenko.livejournal.com/18794.html
For best perfomance @520 MHz increase all dimensions by 30%


4-bay for 15-16 dBi and 6-bay for 16-17 dBi

https://ypylypenko.livejournal.com/31186.html
https://ypylypenko.livejournal.com/31281.html
https://ypylypenko.livejournal.com/33045.html

~13 dBi is possible with Double BiQuad
https://ypylypenko.livejournal.com/2816.html

The most powerful Gray-Hoverman (N10 version with 20 reflector rods) gives 14...15.5 dBi
https://ypylypenko.livejournal.com/3736.html

Last edited by Yurii Pylypenko; 2018-12-12 at 04:19 AM.
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post #5 of 14 (permalink) Old 2018-12-12, 05:04 AM
 
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Quote:
Specs from Channel Master shows about 14dBi gain on channels in the lower 20's for the 3020.
Here is monstruous 24 director + Corner reflector UHF TV Yagi (industrial version)
https://ypylypenko.livejournal.com/10000.html

It's peak gain is >17 dBi, but <12 dBi below 570 MHz and <10 dBi below 500 Mhz

Channel Master claim UHF Gain 9.5dBd (11.5 dBi)
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post #6 of 14 (permalink) Old 2018-12-12, 05:49 AM
 
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to better understand gain/directivity.

Aperture (absorbing area) of any antenna is mathematically linked to it's directivity.




For f=520 MHz (lambda = 0.577 m), aperture is related to gain as follow:


17 dBi is a square 115x115 cm

Aperture efficiency for screen-type antennas typically is 60...200% related to it's reflector area

FF6 VDAR (for new US band) has peak efficiency 192% @ 540 MHz:


Absorbing area: 1.2868 m2
Realized gain: 17.2 dBi (52.47x times)
Frontal projection: 0.669 m2 (87.8 x 76.2 cm)
Aperture efficiency: 192.35%

192% is extremely good efficiency, this mean that FF6 VDAR is extremely compact antenna (for given gain).

Gray-Hoverman has very poor efficiency (is not compact, for given size it has low gain, for given gain it has huge size)

The most optimized N10 version has frontal projection 1112x1184 mm (1,3167 m2 area), but only 31-63% of this area absorb energy


despite being huge, only 14-15.5 dBi directivity

this drastical efficiency is due to extremely high backward radiation (about +8 dBi rear lobe)


This happens because half-waves dipoles are moved from reflector center to reflector edges.
Due to this, central part of antenna doesn't take part in absorbtion/radiation (waste of space) and reflector is too small to prevent rear lobe, because dipoles are moved far away to sides, so you need even more wider reflector to stop backward radiation

Last edited by Yurii Pylypenko; 2018-12-12 at 06:33 AM.
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post #7 of 14 (permalink) Old 2018-12-14, 07:58 PM Thread Starter
 
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Quote:
Channel Master claim UHF Gain 9.5dBd (11.5 dBi)
You are, of course, correct about that, which is more in line with what I would expect. I now see where I was mistaken. Was looking at the gain chart for the Xtreme Signal HD8200XL antenna with a slightly smaller UHF section. https://www.solidsignal.com/pview.asp?p=HD8200XL

Yurii Pylypenko thanks for the detailed gain vs antenna size explanation.

I'm eager to see what holl_ands is able to provide as a narrow band four bay designed for channel 22.
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post #8 of 14 (permalink) Old 2018-12-15, 04:39 AM
 
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your 16 dBi target can cover wideband FF6 or "narrowband" (NEW US band) FF4:

https://imageevent.com/holl_ands/mul...pmjnvwy1.cat_s

best SWR and best directivity is in 570-620 MHz range

increase all dimensions (TR line gap and wire diameter can be the same) by 600/520 = +1.154x
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post #9 of 14 (permalink) Old 2019-01-10, 09:31 PM Thread Starter
 
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Quote:
Originally Posted by Yurii Pylypenko View Post
(TR line gap and wire diameter can be the same)
Is this always true when scaling? Or is it just so in this case since the scale ratio is so small?
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post #10 of 14 (permalink) Old 2019-01-11, 12:31 PM
 
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Quote:
Is this always true when scaling? Or is it just so in this case since the scale ratio is so small?
it's true for any EM-device (not only antennas, including cables, transformers, combiners, filters etc) even for converting 50 MHz antenna to 50 GHz
the only rescaling problem is that ALL dimensions must be resized. ALL mean literally ALL, including but not limited to:
- wires, stripes, sheets diameters, thicknesses etc
- dimension of all dielectric and supporting structures, all hardware (bolts, nuts, washers - diameters, thicknesses, heights)

Typically, developer wants "selective rescaling" - to keep material dimension constant or use preferred materials. E.g. if 50 Mhz antenna uses 10 mm pipe, so 5 GHz rescaled antenna should use 0.1 mm pipe. But you don't want 0.1 mm pipe, you want at least 2 mm pipe (increase diameter dimension 20x times, which is equivalent of 200 mm pipe @ 50 MHz)

Some dimensions are completely insensitive to this. E.g. reflector sheet thickness or reflector rods diameter has neglicible influence on any parameter.
Some dimensions are frequency independent. E.g. homogeneous transmission line (symmetrical or unbalanced) has Zo which is frequency independent (150 Ohm line is 150 Ohm @ 50 MHz and @ 5 Ghz)
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post #11 of 14 (permalink) Old 2019-01-11, 01:46 PM Thread Starter
 
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So... all means ALL except when it does not mean all. I suppose that makes some sense. Seems there a dimensions that are critical, such as element length & spacing, spacing between elements and reflector, then some not so important, such as diameter of elements and feed point gap, (within reason, of course).

Keeping the same transmission wire gap would certainly make for an easier build. I hope the same can be said for using a 1"x2" mesh grid reflector. The material I have is 36" wide (which I feel is wide enough), while scaling to a lower frequency calls for a wider reflector. I notice that when holl_ands re-scaled his NEW FF4 for the new UHF band the width of the reflector width stayed the same, though it's height was increased.
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post #12 of 14 (permalink) Old 2019-01-15, 05:44 AM
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CH22 FF4 4-BAY-BOWTIE with VDAR

I just uploaded 4nec2 analysis of FF4 Optimized for [JUST] Ch22. This first alternative ONLY Optimized Gain [18.2 dBi] and SWR [Under 2.0], leaving F/B & F/R Ratios [12.3 dB] to be whatever they tuned out to be...(same as nikiml's approach to many of his models):
https://imageevent.com/holl_ands/mul...44baybowtiedar

BTW: Ch22 VDAR Size is same Width and Shape, but TWICE as Tall as Full UHF Band FF4+VDAR. I was surprised to see that the Optimizer found Different Dimensions for the Inner and Outer Bowties....so go figure....I expected that they would all be the same, resonating on the same Frequency.

I've also run an Optimization for Gain, SWR, F/B & F/R Ratio....but I think it gave away TOO much Gain in order to meet my stipulated Target of 20 dB F/B & F/R Ratio....I'll try again with revised Targets to see if I can find a better compromise.....

Antenna Simulations, Overload Calculations, etc: http://imageevent.com/holl_ands
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post #13 of 14 (permalink) Old 2019-01-17, 08:29 PM Thread Starter
 
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Hey holl_ands... Nice job! That is just what I was looking for!
Quote:
Originally Posted by holl_ands View Post
[B]I was surprised to see that the Optimizer found Different Dimensions for the Inner and Outer Bowties....so go figure....I expected that they would all be the same, resonating on the same Frequency.
The overall size is almost exactly what I was expecting, but I too was a little surprised by the different sizes (although it's only slight) of the inner and outer bow-ties. Was also surprised that the feedline separation is MUCH SMALLER than even the NEW FF4. Had I just scaled the original up in size for 521MHz, I would have ended up with a much wider gap. Also, I think simply scaling the original FF4 or H2 up in size for Ch22 would have indicated having the reflector screen a little farther back from the elements than your model shows. Plus I would have been working with the flat reflector and bow-ties of the original H2 anyway. BTW, does the VAR serve to increase gain by focusing more energy on the elements? I would have thought flat reflector and flat bow-ties providing a consistent gap over their entire area would have produced more gain at a single frequency. But who am I to question the modeling software...after all, it indicates the kind of gain I was looking for.
Quote:
Originally Posted by holl_ands View Post
[B]I've also run an Optimization for Gain, SWR, F/B & F/R Ratio....but I think it gave away TOO much Gain in order to meet my stipulated Target of 20 dB F/B & F/R Ratio....I'll try again with revised Targets to see if I can find a better compromise.....
Lower F/B & F/R ratio doesn't bother me as long as I'm getting maximum forward gain. But then, I'm not sure I have a good grasp on the impact of F/B & F/R ratio anyway.
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post #14 of 14 (permalink) Old 2019-11-12, 06:31 PM Thread Starter
 
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Here we are, almost a year later, and I've finally got around to building and installing the monster CH22 antenna designed by holl_ands. I found it almost impossible to build to a close tolerance as far as dimensions, but it does deliver more gain that the GH I scaled to channel 22 a couple of years ago, with a target gain of around 16dBi, so we may be close to the target 18.2dBi.

Here is how it looks mounted on my 40ft tower. The bottom of the antenna is about 27ft above ground level, which puts the top of the antenna about 35ft AGL. Yep, that's an 8ft tall 4-bay antenna!

Cham, Yurii Pylypenko and cuivreux like this.
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