GH for UHF (Plans, Parts Lists, Build Tips by 300ohm) - Canadian TV, Computing and Home Theatre Forums

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post #1 of 77 (permalink) Old 2008-04-21, 02:28 AM Thread Starter
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Arrow GH for UHF (Plans, Parts Lists, Build Tips by 300ohm)

And a close up of some of the details.

As you can see from the holes, I can switch the element gap from 44mm to 85mm in about 10 minutes. (when I do, the element to reflector gap decreases by 3mm)

I tried to do a 44mm to 85mm gap comparison today, but because of storms, the atmospheric conditions changed drastically, so Ill have to retest. Initially after changing from 85mm to 44mm, the reception seemed worse. But then after 15 minutes, the picture seemed better. Channel 57 reception remains surprisingly good. And Im connecting up with low loss 300ohm twin lead, naturally.

I may make 3 pairs of bowties to stick in as per EllisGLs post because I can do it easily, but I dont expect much benefit from it.

Last edited by 300ohm; 2008-04-21 at 03:09 AM.
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post #2 of 77 (permalink) Old 2008-04-22, 09:20 PM Thread Starter
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Sagging ??

If you mean on the stubs, my big nylon cable tie support is a very tight fit on the 3/8" tubing (I think the tubing is a hair more than 3/8") and is pretty stiff for its short length. It will stop the stub sagging if a bird like a blue jay or robin or sparrow lands on it, but certainly wouldnt be effective against a seagull or buzzard or raven. (Yes, those birds have torn off many antenna elements of mine. )

If the fit on the tubing was loose, I could correct that by an aluminum pop rivet in the back.
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post #3 of 77 (permalink) Old 2008-04-29, 12:18 AM Thread Starter
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I am able to pick up other channels that I couldn't before with the DBGH.
Yep, the model predicts (example at channel 30) about 13.25 db gain with the SBGH colinear rods versus only 11.75 db gain with the DBGH array only.

For an attic installation, thats a nice easy, economical construction method you used. I assume you drilled holes in the the 2 x 4 for the reflector rod insertion only to the depth where you leave a 20mm gap between the reflector rod sections. A dab of cheap construction adhesive will insure that the reflectors stay put.

Now all you got to do is make a cross from a couple of 2 X 4 pieces (or 4 pieces for a swastica) for a base and you have a nifty rotatable attic setup.

Last edited by 300ohm; 2008-04-29 at 12:33 AM.
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post #4 of 77 (permalink) Old 2008-05-15, 11:17 PM Thread Starter
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Finally finished my 2nd SBGH made from 1 inch sch 40 pvc (which is exactly like the first) and attached my first one to it, making it a DBGH, giving a nice increase in reception. I used 10 gauge copper wire for the phasing feed line (thanks DogT for the wire straightening tip, it worked great) and stainless steel screws, nuts and bolts throughout. I also spray painted all the pvc mast parts with a coat of flat black paint to increase its longevity and make it less visible on the roof, not to mention covering up some sloppy glue work.
I still want to attach with some nylon ties, 8mm fiberglass camping tent poles I have lying around to stiffen up and keep straight all the colinear rod reflectors. And I still need to make up 4 four more stub spacers for the new section. Then I can put the thing up on the roof and do a better comparison.

Right now, testing with the lowest reflectors only about 5 foot off the ground, I did notice the bigger increase in channel 17 reception versus the SBGH, like predicted by the model. My channel 57 reception also increased slightly, but the increase in reception wasnt nearly as big as with the lower channel 17. I also picked up channel 48 which the SBGH couldnt, also kind of like bump in the curve predicted by the DBGH model, (even though there is also a overall increase in gain with the DBGH).
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post #5 of 77 (permalink) Old 2008-05-27, 09:41 PM Thread Starter
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I finally got my DBGH up on the chimney mount so I could test with digital.


I put a tight fitting broomstick up inside of it and attached some 1/2 inch u-channel on the back, so its very stiff and doesnt sway in a 20mph breeze. Those black rods across the reflectors are old fiberglass tent supports, stiff and very light, and attached with nylon wire ties. The whole thing, including the bottom mast part, weighs 11 lbs. I used 85mm feed-gap spacing (the distance of a 1 inch pvc tee, handy) and have a reflector to element spacing of 105mm. The feed-line spacing gap is 20mm, I assume to maintain 300 ohms and the feed line is 10 gauge copper. Thats a 1/2 inch pvc tee in the middle for the line connection point, but the rest is all 1 inch pvc plastic parts spray painted flat black. The aluminum reflectors and elements were left unpainted, even though Ive read its OK to paint those too.

I still havent seen a bird roost on the 8 gauge aluminum elements. The way I figure it, since they have a 10mm roosting point nearby, theyll always choose the reflector rod instead. 8 gauge wire is hard for them to get a good balance.

Un-amped, I get strong and consistant digital reception on all the Philadelphia stations 60.8 miles away, with the exception of virtual channel 12 (real channel 50, -115.0dBm per TVFool) Its going back to real channel 12 at -100.2 dBm on 2/17/09 so thats not going to be a problem, (except for making a vhf antenna for it and real channel 6).

I also get strong and consistant digital reception of virtual channel 6 (real channel 64 right now, -85.0dbm) and virtual channel 10 (real channel 67 right now, -85.9dBm, will go to real channel 34 -85.3dBm 2/17/09)

I also occassionally get some Salisbury MD stations (-92.0dBm and -97.3dBm) coming from the back. So all in all I get about 33 to 37 channels, counting sub-channels in that one fixed position 25-30 feet in the air, aiming thru the middle of two large maple trees. And Im using an Zenith/Insignia NS-DXA1 CECB converter box.

Last edited by 300ohm; 2008-05-27 at 10:32 PM.
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post #6 of 77 (permalink) Old 2008-06-01, 09:44 PM
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New Builder

I am new to this forum and have very little experience with antenna building. I did build one of the quick UHF antennas from the video on YouTube and was amazed that it actually worked. It is kind of crude and built with supplies that I had around my studio. My studio is usually a mess of thing that I have collected that "must be good for something"!

This forum on the Gray-Hoverman is very impressive and I have read about half of the posts and want to build one of these antennas and see if I get an increase in digital channels that I can pick up. I just won some aluminum wire on ebay that I hope will work for the diamond shaped parts.

I also have an old FM radio antenna that I have had laying around for many years. It is a traditional horizontal antenna with elements made of aluminum tubes. I was hoping that these tubes will work for the reflectors, what do you think. Also will the aluminum ground wire work for the diamonds?

Thanks for any help,

Frank
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post #7 of 77 (permalink) Old 2008-06-01, 11:42 PM Thread Starter
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It is a traditional horizontal antenna with elements made of aluminum tubes. I was hoping that these tubes will work for the reflectors, what do you think. Also will the aluminum ground wire work for the diamonds?
3/8 inch aluminum tubes and 8 gauge aluminum ground wire will work perfectly.
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post #8 of 77 (permalink) Old 2008-07-10, 10:51 PM Thread Starter
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Thumbs up SBGH Plan, Parts List, Cut List, and Construction Notes by 300ohm



Parts List
====================================================
2 - 10 foot pieces of 1/2" sch 40 600psi pvc pipe.
2 - 1/2" sch 40 pvc elbows.
1 - 1/2" sch 40 pvc cross.
17 - 1/2" sch 40 pvc tees. (Buy 2 contractor 10 packs)
30 - Nylon wire ties. (Buy a 50 pack)
36 - 1/2" x #6 plated wood screws. (Buy a 50 or 100 pack)
2 - 5 foot pieces 6 gauge solid copper wire. (This is $.84 a foot at Lowes. Buying just one 5 foot piece of 10-2 solid wire and stripping it will save approx 60% and is stiff enough with the stub holders.)
1 - 30" by 40" 10 gauge piece of fencing, 2" X 4" grid or less. (1" x 2" would be ideal as it would give about 1/4 db more gain at channel 17, about 1/2 db more at channel 40, but it would decrease my chances of reception of channel 36 Atlantic City about 180 degees east)
2 - 1 1/4" ID u-bolts to clamp antenna to mast.
4 - #10 x 1" stainless or brass pan head screws.
2 - #10 x 1 1/2" brass bolts. (for least galvanic corrosion at connection point)
4 - #10 brass nuts.
10 - #10 brass or copper washers.
1 - Tube Plumbers Goop. (Or Loctite Plumbers and Marine Adhesive or plumbing PVC cement or epoxy or even plastic model glue, this is antenna work not plumbing.)

Miscellaneous and Beauty
=======================================
4 - Sch 40 pvc caps.
1 - Can of flat black spray paint.
1 - 300ohm to 75 ohm balun
Length of RG6 cable and ends to suit.


Cutting List
===========================
A) 4 pieces @ 3 7/8"
B) 4 pieces @ 8 1/2"
C) 4 pieces @ 3 5/16"
D) 4 pieces @ 4" * (These stub holder pieces are just pushed in, not glued or screwed.)
E) 2 pieces @ 37 9/16"
F) 2 pieces @ 8 3/8"
G) 2 pieces @ 8 3/4" # (This gives a 10 inch (254mm) spacing between element inside angles)
H) 6 pieces @ 2 3/8" *
I) 3 pieces @ 1 3/4" # (This gives a reflector to element spacing of 100mm)

>>>>>>>>>>> Push all pipe into fittings 5/8" <<<<<<<<<<<<<<<

# = Critical Size
* = Not a Critical Size

I havent yet priced all the items, but I figure its somewhere about $25 if everything had to be purchased. My out of pocket costs were only about $12, as I had a lot of the stuff. The Channel Master 4221A would cost me $23.99 plus 15.95 UPS ground shipping for a total of $39.94 from SolidSignal. But wheres the fun in that ?????

My builds/plans (not the latest models) are located here.

Last edited by 300ohm; 2008-07-10 at 11:57 PM.
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post #9 of 77 (permalink) Old 2008-07-10, 10:54 PM Thread Starter
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Construction Notes



Construction Notes
====================================
I predrilled with a 3/32" drill bit, the holes for the 1/2" #6 plated wood screws. All screws were attached to the fittings on the backside, ie the reflector side, to minimize the effect of the screws on the antenna. (see picture) No screws were used for the building of the cross-pieces, they were glued. No screws were used for the "stub" holder, its just a press fit (its not going anywhere).

I predrilled with a 1/8" drill bit, the holes for the 1" #10 stainless pan head screws in the top and bottom cross-pieces. The element rests on the plastic and there is a brass washer between it and the pan head of the stainless steel screw.

I predrilled with a 3/16" drill bit, the holes for the #10 x 1 1/2" brass bolts in the middle cross-piece. The element also rests directly on the cross-piece, then a brass washer, then a brass nut is used to secure the element. Then 2 brass washers and a brass nut are attached for connecting the antenna balun between those 2 washers.
The holes on each cross-piece were drilled centered, on the cross-piece exactly 100mm apart (50mm on each side of center). This gives an air space between the wires of 88mm (93mm center of wire to center of wire) using 6 gauge solid copper wire. (Using 10 gauge wire will widen the distance)

Bending Jig
====================



I used that scrap piece of wood to keep the rest of the antenna flat while bending it around the nail. (6 gauge solid copper wire is pretty tough to work with, glad I didnt use 4 gauge, heh)
For the cross-piece jig, so that the cross-pieces would be perfectly aligned, I made a crude version of Bix2's cross-piece jig pictured earlier in this thread.
And that full sized drawing on scrap cardboard of one of the antenna elements came in very handy.

My builds/plans (not the latest models) are located here.

Last edited by 300ohm; 2008-07-11 at 12:35 AM.
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post #10 of 77 (permalink) Old 2008-07-11, 11:05 AM
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Nice Job 300ohm...

I've been on vacation and just getting back.

The 1/2 in. pvc with the additional support, for the ends of the elements, will make a nice strong outdoor antenna. Also lighter.

The cross and tee's at the bottom make it easy to combine 2 SBGH's into a DBGH.

My 3/4 in. pvc attic antenna's have an additional 63.5 mm on the top and bottom, so they can be combined into a DBGH. I clamp them to a single pipe.

Your design makes it easier.
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post #11 of 77 (permalink) Old 2008-07-11, 11:42 AM
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300ohm, I've seen a few remarks you've made regarding grid reflectors (or drilling holes in a solid reflector to create one), and I'm a bit confused:

This might be ignorant of me, but I was always under the impression that the main goal with a grid reflector was to make the gap between the horizontal members smaller than the wavelengths of the desired frequencies, so that the grid would appear as a solid surface.

In other words, if you had simply vertical members | | | | with small enough gap, then that would make a good reflector for horizontally polarized signals, but if you flipped it sideways to get =, then you would only get reflections off those individual, horizontal members.

Is that just way off then?
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post #12 of 77 (permalink) Old 2008-07-12, 10:30 AM
 
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300ohm
Thanks a lot for posting that.

Question - what is the purpose of using the tubing and brackets - couldn't I just make a frame of wood and attach wire meshing to that? Looking at yours and DogT seems they both use this piping and I was wondering if that is by choice or if there is a reason behind it...thanks!
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post #13 of 77 (permalink) Old 2008-07-12, 12:04 PM
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Wills

Wood is just fine. If the antenna is used outside, you need to preserve the wood. You may need to drill some 1 in. / 25 mm holes, to make the wood lighter. PVC is light weight, and it is an insulator, at radio frequency. 300ohm has his antenna's outside. He needs to consider wind and ice load. PVC pipe has long been the choice of ham radio operators, for antenna construction.
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post #14 of 77 (permalink) Old 2008-07-12, 12:51 PM Thread Starter
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Quote:
Question - what is the purpose of using the tubing and brackets - couldn't I just make a frame of wood and attach wire meshing to that? Looking at yours and DogT seems they both use this piping and I was wondering if that is by choice or if there is a reason behind it...thanks!
A couple of things,

1) 1/2 inch sch 40 pvc @$1.67 for 10' is cheaper than a 2 x 4 x 8 at over $2.(and actually, using the correct temperature, it can be bent at 90 degrees, so I could have saved some costs there, but its tricky with the temps) And like Bix2 said, its light weight and rot resistant. (and generally will last outdoors 5 -7 or so years. More if painted.) As you may note, my goal is to get the cost down to less than a CM 4221a, if everything is purchased.

2) Wood or metal is fine for the reflector frame, but because of the moisture content of wood, you dont want the elements to rest on wood. They should rest on something completely electrically inert, like a plastic.

Quote:
This might be ignorant of me, but I was always under the impression that the main goal with a grid reflector was to make the gap between the horizontal members smaller than the wavelengths of the desired frequencies, so that the grid would appear as a solid surface
Yes, for more forward gain and a greater front to back ratio, at 700 mhz (channel 52) the grid should be less than an inch to approximate a solid surface. But in my case, I have stations North South East and West, so I dont want that greater F/B ratio.

Quote:
In other words, if you had simply vertical members | | | | with small enough gap, then that would make a good reflector for horizontally polarized signals, but if you flipped it sideways to get =, then you would only get reflections off those individual, horizontal members.
North American TV is horizontally polarized, so you want = = = horizontal reflectors. With a small enough gap/hole, I guess it doesnt matter, but the idea with the holes in sheet metal is to let the wind thru, so you would want larger holes for less wind resistance.

Quote:
The DBGH grabs CTV and CBC as where the db4 would depend on the day. Maybe i can join them?
Not a good idea, it would pretty much guarantee worse performance than the db4 or DBGH by themselves. (unless you get lucky by some act of black magic)
Your DBGH should perform well above the db4. Try another balun and double check all measurements and flatness and straightness.

My builds/plans (not the latest models) are located here.

Last edited by 300ohm; 2008-07-12 at 10:29 PM.
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post #15 of 77 (permalink) Old 2008-07-14, 11:19 AM
 
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Am I sourcing the right parts?

I called home depot - $7.00+ for 10' of the 1/2 inch pvc.

Your post says $1.67, are you going to another place that has a better price that you could share?

Thanks

oh, also, I can get a better deal on 1" or 2" pipe, can I use that?

And.....

I noticed in your post 300ohm that the design is built for south east and west; I will need basically south and a bit east - does that affect the design? I mean do I need a mesh behind it? The guy who just posted his picture on wood has no screen behind it.

Thanks!

Last edited by Wills; 2008-07-14 at 11:41 AM.
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