Success !!! I got the Vhf-Hi gain going the right way with the colinear rod reflector models and with more gain to boot ! (This does not apply to the mesh models, for obvious reasons.)
Using the basic original SBGH gen1 colinear rod plans (with 10ga elements, 3/8 inch reflectors), I placed additional 28 inch, 3/8 inch reflectors 10 inches behind the 28 inch 10 ga NARODs that are 1/2 inch above the stubs. Oddly, using a larger reflector than the driven element, typical in most TV antenna designs, decreased performance, as did a smaller reflector.
The effective bandwidth for Vhf-Hi is somewhat limited to about 4 channels. I tweaked for channels 10 to 13, so if channels 7 to 9 are needed, adjustments have to be made.
The use of the NARODs levels out and dips the gain curve similiar to the SBGH JED Gold Standard model, so the original SBGH gen1 model is so far the best to use in this case so as to not exacerbate the dip further.
I'm planning on building a SBGH 6 using effects build as a guide, except I'm going to have to find a way to add the NARODs and NAROD reflectors to his build.
Yep, looks like about the same figures at slightly different frequencies. Autofils and I generally use the middle of the channel. In VHF though its good to see the tops and the bottoms of the channels too, for example the YA-1713 channel 13 drop off, heh.
I'm planning on building a SBGH 6 using effects build as a guide, except I'm going to have to find a way to add the NARODs and NAROD reflectors to his build.
Yeah, thats a nice build, almost identical to mlords builds.
For the NAROD to stub holders with #6 wire, you could use small thin stiff pieces of plastic (vynil siding cut to about 1 inch by 1/2 inches pieces comes to mind) with holes drilled in them at 1/2 inch on center, drilled just slightly smaller than the wire diameter (9/64ths drill bit ?) so that they can still be slipped on with a little force. I would say about 4 per NAROD would hold nicely. A dab of Plumbers Goop (basically thick model airplane cement) could be used to permanently hold them, if need be.
For the NAROD reflectors, additional tees and 1/2 inch pvc pieces could be used. My slip on tees would work nicely and allow you to adjust the NAROD reflectors until they are perfectly parallel to the NARODs. Then a small #4 screw can hold the tees etc in place.
Im a bit confused. Which plans are the best to use? I am looking at this thread, but see 2-3 different kinds of antennas posted in the pictures. I like the look of the curved antenna, is this a good one?
I thought the Oroginsl DBGH had only 1 set of coliner reflectors at the stack joint insread of the 2 shown, 11 pair total. I 've got an unfinished carboard & coathanger project with 11 pair in place that I plan to convert.
What would happen if you ganged two SBGHs horizontally with the mesh reflectors touching? Would it result in any VHF-high gain? What would happen to UHF gain?
I am asking since this is how the CM4228 achieves VHF-high gain.
The following is a quote from HDTVprimer:
"This antenna (CM4228) is advertised solely as a UHF antenna. But, as many people have discovered, it has strong gain for VHF-high, especially channel 9-13. What gives it this ability is the continuous screen. Other 8-bays have a reflector that is not continuous across the right and left halves. Those antennas have little usefulness for VHF channels.
The continuous screen is not simply a reflector for these channels, but rather it becomes the primary radiating element. As a result, radiation out the back is very strong, nearly bi-directional for some channels."
If there is the possibily of VHF-high gain, is anyone interested in modelling it?
What would happen if you ganged two SBGHs horizontally with the mesh reflectors touching? Would it result in any VHF-high gain? What would happen to UHF gain?
I am asking since this is how the CM4228 achieves VHF-high gain.
I used the Combo Hi-VHF & UHF capability to investigate what happens if insulated
AWG10 wire is used instead of Bare wire....it wasn't very pretty....(NARODS were left Bare).
FYI: In NEC, fol. Loading card adds 24 mil PVC coating on top of AWG10 for each GW#:
LD 7 GW# 0 0 4.5 0.075
Repeat as necessary for all affected wires....
I need to clarify my terminology for you. The NARODS are only the 4 wires directly above the stubs. (I have them split into 2 pieces each on the model to investate the effects of slanting them). The term NAROD stands for Not A Reflector Or Director. I coined the term because I dont know what else to call them. NARODS are interesting little animals. They are having some kind of a drastic capacitance or current effect on the GH driven elements.
The rest of the wires are reflectors or driven elements. (the wires 10 or so inches behind the NARODs could be called NAROD reflectors). So in the model you link to, there are only 4 NARODs and 4 NAROD reflectors, installed on DBGH gen 1 co-linear rod 12 pair model.
The vhf-hi bandwidth is narrow, hence the need for 3 different models. And if youll notice, the max vhf-hi forward gain can flip direction 180 degrees on some of the off channels.
From my actual builds in the past (other designs) Ive always noticed that bare wire performs better, so Im not surprised by your results. Bare wire also gives the antenna more of an antenna look, instead of a bunch of (different colored in my case) house wire thrown together, heh.
I have added vertical wires (alligator clips with 18 gauge) to NARODS (29.5"). This makes a loop around the driven element. It seems to reduce analog ghosts on the weak Ch. (NM -8). I'm running gen. 2 GH fractal with Al.-foil reflector (15") and NARODS reflectors at 11.5" spacing.
Is your nec file mistakenly back in meters?
See the GS instruction, if you have any.
The nec files of 300ohms earlier are in inches and show a GS scale of 0.0254.
I set a DB4 model to add the
LD 7 0 0 0 4.5 0.075
(GW# of 0 means all wires)
and when I clicked on a wire, the popup box showed me I had 75mm of coating!
So be sure you have the right units.
In a metric file, (no GS scale), I have
LD 7 0 0 0 4.5 0.001905
that is 1.905 mm outer radius.
The simulation show no noticeable change. Coating has no visible effect.
Sorry.
Thanks for pointing out my error....that's the second time I've fallen into the "GS Trap".
Anything BELOW the GS Card has to be in meters. And GS Card doesn't directly apply to SY Cards...
Adding 45mil PVC insulation coating (e.g. THW AWG10 house wire), caused significant
impact above Ch47 to both Raw Gain and additional Net Gain Loss due to increasing SWR.
I was surprised to see impacts to Ch7 and adjacent out-of-band region.
Although it did not adversely impact the DBGH design, it could impact other designs.
have added vertical wires (alligator clips with 18 gauge) to NARODS (29.5"). This makes a loop around the driven element. It seems to reduce analog ghosts on the weak Ch. (NM -8). I'm running gen. 2 GH fractal with Al.-foil reflector (15") and NARODS reflectors at 11.5" spacing.
Quick modeling shows that should give you about .25 to 1.5 dBi less gain with a higher SWR, so net gain would be even less. I didnt see hardly any change in the radiation pattern either, so I cant explain less ghosts. Ghosts are tricky and can be caused by many things, even the placement of the coax and balun.
Here's the 4nec2 file for Insulated AWG10 in DBGH with 28 (Bare) Reflector RODS:
[I was also tempted to round off excessive precision...cuz it clutters up the listing.]
[I hope 300ohm is happy with "Reflector RODS" instead of "NARODS".....]
[So are GW42-49 crosswires the "NARODS"???]
Adding 45mil PVC insulation coating (e.g. THW AWG10 house wire), caused significant impact above Ch47 to both Raw Gain and additional Net Gain Loss due to increasing SWR.
I was surprised to see impacts to Ch7 and adjacent out-of-band region.
Although it did not adversely impact the DBGH design, it could impact other designs.
I am not quiet sure why you put 45 mil of PVC on gauge 10; it certainly is not that thick. The gauge 12 is likely correct at 27 mil, but the 10 gauge I have here is berely thicker, but not twice. Nevertheless, even with exagerated thickness of 47 mil of coating of 4.5 relative dielectric constant, I tested your nec file with and without the wire insulation (the only diff between the 2 simulations is that I deleted the LD 7 line, as expected).
I observe a shift to the left of the spectrum response, as expected since the coating does reduce the velocity factor and thus virtually make the wires longer, therefore suitable for lower frequencies.
I did a frequency sweep, from 48MHz to 900MHz by steps of 12 MHz, on the frontal gain (elevation 0, azimuth 90). The non uhf bands already sensitive to marginal antenna attributes are changing the most. The UHF band is pretty similar though.
If the simulations were not taking so long on my crawling PC, would test with 34 mil of coating. Given the DB4 simulation with 27 mil of coating didn't show any noticeable diff, that 2 design in 2 that are not largely influenced by wire coating. See results on
AVS Forum > HDTV > HDTV Technical > How to build a UHF antenna... , Post 1556.
(sorry for lack of url, can't post images or link here...somehow).
Here's spec sheet for "THW" building wire showing 45 mil insulation thickness,
bringing the total AWG10 O.D. from 0.105 (bare) to 0.195 inch (coated): http://www.pittsburghwire.com/pdf/CatalogF4.pdf
Hence "coat radius" is 0.0975 inch = 0.00248 meters (according to WinConvert).
=====================================
AWG10 "THW" is solid copper wire with a single layer of PVC insulation...no extra jacket.
Readily available at my Home Depot....
From your instructions, I built a Gray-Hoverman about 2 weeks ago and put it in my attic, and with a 24 dB amplifier and with VERY careful aiming (106 degrees) am able to pick up Buffalo's Channel 2 at 76.5 miles. Since it was going in the attic, I mounted the elements on a scrap of plastic sign board material, each secured with shipping tape and plastic wire ties. Didn't find suitable copper wire at Cdn Tire, so used 1/4" icemaker copper tubing. Found it easy to bend precisely using the recommended jig -- got very symmetrical elements. Does hollow tubing change your receive models?
The GH sensitivity was only marginally better than a DB4 coathanger I built in December until in desperation I hung an aluminum foil-covered (24" X 32") reflector about a foot behind the GH, and that made a big difference. Signal strengths ran about 60 to 62 (orange level) and solid for a couple of weeks, but during the Super Bowl WGRZ must have increased the power, for signal strengths during the game ran 70 to 72. Approximately 3+ minutes before the end of the 4th quarter the signal failed completely and I had to switch over to cable. After about 30 to 45 seconds it came back on to about 70 strength and stayed rock solid the rest of the game. Today it is back to around 62. It was a real pleasure to watch the game in "pure" form without the stupid interjections from local greedsters.
Thanks to the Forum for teaching me so much about DTV reception and the construction of an effective antenna. (Can furnish photos if anyone can tell me how.)
Nope, the signals are resonating on the outside metal skin for the most part.
Approximately 3+ minutes before the end of the 4th quarter the signal failed completely and I had to switch over to cable. After about 30 to 45 seconds it came back on to about 70 strength and stayed rock solid the rest of the game. Today it is back to around 62.
In cases like that typically some large metal object came in between you and the station. It happens to me too because of shipping in Delaware Bay, heh.
Hello Everyone, I have started to build the antenna based the the photos here: http://imageevent.com/holl_ands/grayhoverman
Can someone give me a more precise measurements on the element spacing ?(Where the phasing line connects)
It looks like just under 4 inches (based on 1 inch squares) but it's hard to tell.
The phasing lines look like they are 2" apart by 1" height, do they connect on a taper to the elements ?
I did see other diagrams with more label dimensions but wasn't sure if they apply to this design.
Please forgive pickiness but I used to be a machinist (now a hobby) so I'm used to working with tight tolerances.
Any detailed measurements would be greatly appreciated.
Thanks J
P.S. That software you guys use for modeling, can it export 3D CAD data ?
Thanks for clarifying the dimensions. I am working on a slightly different layout for the 1/2 PVC pipe than I've seen so far, I think you will like it!
So far I have to settle for #10 wire for the elements, I have called 6 major electrical suppliers in Toronto Canada and none of them have it. If any Canadians out there have found #6 or #8 solid copper wire please let me know where.
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