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I would appreciate the difference between the 2 alternatives.
The difference in gain between #6GA solid wire or #10GA or 1/4" OD copper tubing is very small. Holl_ands has the 10 gauge data posted in the above link.

The thing to be careful about using different wire sizes is to maintain 6 - 7 mm between the surfaces of the stubs and the NARODs.

In that DBGH model, be aware of the dip in the uhf gain curve. If you dont have any channels (or strong channels) in that dip, then the straight NARODs are fine for you, and make building easy.

Models that have eliminated the dip are found here :
http://clients.teksavvy.com/~nickm/gh_n3_uV.html
 

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Discussion Starter #3
Oh! I see, the 3D PDF drawing mentions 6GA for the driven elements but the simulations (NEC files) were done with 10GA. Then, the Gain, SWR and impedance plots were generated with 10GA wire, right?

If I understood correctly, I should not bother with the 1/2" c/c dimension between Narods and driven elements but rather 6-7 from surface to surface... but what about the other dimensions refering to c/c? (as per example: 4.13, 5.00 and 1.00 for the phase lines)

I prefer the straight Narods to maintain the VHF-HI gain.

Regards,
 

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If I understood correctly, I should not bother with the 1/2" c/c dimension between Narods and driven elements but rather 6-7 from surface to surface...
The is correct and it seems to apply to all NAROD models - bent or straight.

but what about the other dimensions refering to c/c? (as per example: 4.13, 5.00 and 1.00 for the phase lines)
Those are not as critical, so use them as they are - center to center.

I prefer the straight Narods to maintain the VHF-HI gain.
if you build this GH10n3 top-hat narod model you'll get similar on average gain antenna but with half the size.

Here's how the NET gain compares ( *shows the better value):
Code:
		DBGH		GH10n3
-------------------------------------		
min vhf		7.3		*9.4
ave vhf		9.3		*9.7
max vhf		*10.3		10.0
-------------------------------------		
min uhf		11.6		*14.5
ave uhf		*16.6		15.5
max uhf		*15.1		15.0
keep in mind the the holl_ands charts show raw gain not adjusted for the mismatch losses.

So unless you really need the peak gain values you'll have more manageable antenna by building the gh10n3.
Also the top hat narod may be easier to attach since it goes through the boom.

HTH
 

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Discussion Starter #7
Hello Nikiml, Hey! thanks for dropping by and for answering my questions, I appreciate very much.
I'm not limited in space, well, I will not build bigger than the DBGH since the antenna will go in my attic and I'm limited to around 6' high if I need to point the DBGH in the right direction. But for sure I want to maximize that available height. I don't bother too much about construction complexity, I'll take the time to do it well.

Yes, I have earlier noticed the GH10n3 performances. Quite interesting but I'd be really interested to see a dual bay version, have you designed any?

When you mention mismatch losses, are you referring the loss if adding the top bay per the drawings?

In my case, VHF channels are close to me and UHF further.
http://www.tvfool.com/?option=com_wrapper&Itemid=29&q=id=c77a7f02b12ba1

Regards,
 

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I know nothing about attic installations... And installations in general...

But if your "pending digital" is correct, then excluding RF 38, you need a bi-directional antenna both in VHF and UHF.

If it was for roof I'd probably try gh4n pointed at 140deg true(155 mangetic) azimuth.

But may be others can suggest better based on your tvfool
 

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you need a bi-directional antenna both in VHF and UHF.
Yep.
I'd probably try gh4n pointed at 140deg true(155 mangetic) azimuth.
Or the GH0n3 at the same direction for a bit wider beamwidth. Too high a gain antenna like the DBGH or the GH10 can hurt the situation. Channels 2, 6, 10, 12 off the back shouldnt be a problem.
Like nikiml said, the oddball channel 38 off to the side is going to be tricky, but at least its fairly strong.
 

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Discussion Starter #10
Theorically, I was figuring the exact same direction (135-140 true) with the DBGH lobing pattern. Fetching the furthest in the USA and the opposite smaller pattern catching the closest ones in Montreal 20 miles from me.

Is software optimization doable for dual bay antennas like the DBGH or doubling the GH10n3 or GH4n? Has anyone done it yet?
 

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Discussion Starter #11
Please explain a bit how can a higher gain antenna like you refer to, hurt the reception? Is it because the lobing pattern is more directionnal? Not sure I got you on that one.

38...I can't have them all. ;0) If I can get the most on these 2 directions: 159 and 305 (true) I'll be very happy.
 

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Leoparleur,

You're trying to kill a mosquito with a gun! I also live on the south shore of
Montreal and I can pick up every digital station down to WFFF with a simple Stealth Hawk antenna in my attic, even if I'm farther from the US border than you. Here's my TvFool.

My next project is to build a SBGH0n3 like 300ohm said in order to try to get WVNY. Please note that WVNY as co-channel, adjacent channel, and FM 2nd harmonic interferences all at once, so maybe my antenna is not to blame here. Some of that interference will disappear on the morning of September 1st when the digital transition will be completed and analog stations will stop broadcasting.
 

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Please explain a bit how can a higher gain antenna like you refer to, hurt the reception? Is it because the lobing pattern is more directionnal? Not sure I got you on that one.

38...I can't have them all. ;0) If I can get the most on these 2 directions: 159 and 305 (true) I'll be very happy.
Yes, generally the bigger the antenna the more directional it is. And after the canadian switchover you'll have 3 more channels coming from 100(true). This combined with the fact that most of your signals are either very strong or very very weak suggest that you need wider beam lower gain antenna.

Also, from what I read on this forums, attics and directionality don't go well together...
 

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Discussion Starter #14
You're trying to kill a mosquito with a gun!
What's wrong with that when the purpose is to kill it from 1000ft away, not eat it! ;0) Seriously, in my case, will it be harmful to have a bigger antenna than a smaller one (considering only gain factor between the 2)?
 

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Discussion Starter #15
Yes, generally the bigger the antenna the more directional it is.
Thanks for confirming!

From the polar pattern, I estimate the DBGH will cover the 145 angle dispersion I need. Except if the roof reflects waves in other directions in the attic like you mention. The attic is the solution I'm looking into most. I want it stealth. For sure the roof is not an option for me. I don't want to have an outside antenna on the house and mostly not in the front of house (the house is facing south). I could also try another smaller and less directional design later on the West side if the DBGH doesn't perform well. It wont be as high thought.

The part where I'm not confortable with yet is when estimating, co-channel and adj. channel, I have not done any reading on that subject yet, not sure how it affects reception and what to look for.

Thanks fellows!
 

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What's wrong with that when the purpose is to kill it from 1000ft away, not eat it! ;0) Seriously, in my case, will it be harmful to have a bigger antenna than a smaller one (considering only gain factor between the 2)?
leoparleur,

To continue with your analogy, you're trying to shoot something that's 50 feet away, not 1000 feet away, so you're giving yourself a lot a trouble, especially for a first antenna build. If I were you, I would start by building myself a Stealth Hawk antenna (see the stealth hawk thread, post #289 for dimensions) and see what I can get. It's only going to take you 30min to do so. Like I said, you're closer to the US border than I am. Looking at your Tvfool, I see that you're getting >3.5 dB more on WVNY, with much less interference than I do, so you might even have a shot at it. As for the Montreal stations, don't worry about them too much as they will mostly be very powerful after the transition, so it should be easy to receive them. You might need to play a little with antenna orientation and placement in your attic to find the best spot though, but once that's done, you'll be set.

If after trying the stealh hawk you still want to build a more directional and more powerful antenna, nothing stops you from doing so. You will have gained some valuable experience in antenna bulding and placement meanwhile.
 

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From the polar pattern, I estimate the DBGH will cover the 145 angle dispersion I need.
The beamwidth youre looking for is about 66 degrees at aiming about 140 degrees magnetic, unless youre thinking of giving up on one group of stations. The DBGH doesnt have that wide of a beamwidth, (3db down, the standard way of measuring beamwidth).

I would build a reflector less SBGH version first and try it. You can always build the other half later. :p
 

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Discussion Starter #18
You guys are probably right, It could be more reasonnable to try a smaller one first. But please explain what are the ill effects of building the stronger one first? I want to fetch the most from the USA pointing it in that direction. Yes I am giving up on some channels, I only want my antenna to focus on Montreal 305 and USA 159. The bi-directionnal DBGH covers 146 degrees difference so beeming 140 degrees magnetic is what I had in mind.

Knowing myself, if I build a weaker one, I'll end up building the stronger one anyway just for proof. If there is no ill effect, except than being more directional and longer to build why than should I waste my time doing a smaller one? Please tell me if this has something to do with co or adj channel or problem we have not mentionned yet?

Yes for fun, I will try the Stealth Hawk. Any links to bill of material and pictures?

Thanks,
 

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But please explain what are the ill effects of building the stronger one first? I
I believe that with DBGH you cannot get any more channels from 159 than you'll get with much smaller antenna. Therefore by limiting your beamwith (by building dbgh) you only loose channels.

Probably everyone elses advise was based on that assumption as well.
 

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Yes for fun, I will try the Stealth Hawk. Any links to bill of material and pictures?
You'll find a plan to build a stealth hawk here. I built mine with 5 feet of #10awg copper wire, a cheap balun, a couple bolts and nuts and a small piece of plastic to attach the balun to the antenna.

Like 300ohm and nikiml said, a SBGH0n3 might also be a good antenna for your situation, although a bit more complex to build.

The main idea though is that every location is particuliar, and you'll only know what you need until after you start experimenting. For an attic install, try placing your antenna as high as you can, but avoid placing your antenna close or behind metal objects like pipes, ventilation conduits, etc. Use the shortest RG6 cable you can to connect to your tv and avoid splitters, unless you're willing to use an amplifier in your setup (shouldn't be necessary).
 
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