GH for UHF (Plans, Parts Lists, Build Tips by 300ohm)

300ohm · Apr 21, 2008

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.

300ohm · Apr 23, 2008

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.

300ohm · Apr 29, 2008

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.

300ohm · May 16, 2008

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).

300ohm · May 28, 2008

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.

FrankInFlorida · Jun 2, 2008

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

300ohm · Jun 2, 2008

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.

300ohm · Jul 11, 2008

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 ?????

300ohm · Jul 11, 2008

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.

bix2 · Jul 11, 2008

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.

jmoots · Jul 11, 2008

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?

Wills · Jul 12, 2008

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!

bix2 · Jul 12, 2008

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.

300ohm · Jul 12, 2008

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.

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.

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.

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.

Wills · Jul 14, 2008

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!

300ohm · Jul 14, 2008

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?

Heh, the person you talked to on the phone must have been quoting something completely different. 1/2 inch sch 40 pvc 600 psi is still $1.69 for 10 foot at my Lowes all day long. I checked today (The thinner 200-350 psi stuff is $.20 cheaper per 10 foot.) At my Home Depot, I believe the same stuff is about $.10 more. Normally, the stuff comes in 20 foot pieces. Lowes used to sell it that way for even less per foot. Now they cut it and charge more.

Of course you could use bigger pipe. But for antennas, you have to take weight and wind resistance into account. With heavier pipe, its harder to secure outside. Also bigger pipe and more importantly, the fittings for it cost exponentially more. (ie a 1/2 inch pvc cross is $.82 while a 3/4 inch pvc cross is $2.05)

The compass direction the antenna is going to point to makes no difference on the Grey-Hoverman design.

Ive been using DogT's crossed pvc tee method for all my SBGH builds. For increased rigidity and adjustability, Ive come up with my snap on adjustable, one standoff fits all design, heh. I'll probably use it in my future builds.

By slicing a 1/2 inch sch 40 pvc tee a little less than in 1/2 (leave the larger amount on the tee) creates a perfect snap on standoff for a SBGH used on a common 7/8 in inch OD (3/4 inch ID) aluminum tube. It fits very tightly, yet is removeable. If needed for a permanent mount, it could be screwed, glued or pop riveted. (as can be the the rest of the pvc stuff, but pushing the pvc in all the way makes it very snug) Total cost : appoximately 60 cents per bay for the standoffs.

Other dimensions Ive noticed that could take advantage of this design are :
3/4 inch sch 40 pvc tee - 1 inch OD tube.
1 inch sch 40 pvc tee - 1 1/4 inch OD tube.

Also note in the picture, the saw I prefer to saw pvc with in a miter box, and the washers made from 1/4 inch plexiglass which I used on my present SBGH (for the top and bottom bays only, the middle bay still needs the copper washers) in lieu of four copper washers mentioned in my parts list above.

bix2 · Jul 20, 2008

In post 480, this forum, my friend, installed one of my antenna's in his attic.
http://www.digitalhome.ca/forum/showpost.php?p=753798&postcount=480

He has since described his experience with the antenna on his house work blog.
http://web.mac.com/dfiler/FilerHouse/Work-Blog/Entries/2008/6/15_Week_099_-_2nd_Attic_Antenna.html#7

300ohm · Jul 20, 2008

Well, in a thread at another site a guy made a poorly made DBGH and was getting stations from 110 to 210 miles away, heh.

I pointed it at the hardest to get station and joined the antenna feeds in the basement with a 2:1 coax splitter. With the CM-4221 roughly 160º off of this, I am now able to pull in all of Pittsburgh's digital TV stations along with a couple stations from Johnstown.

bix2, I hope you told him hes losing about 3db doing that. An A-B switch would have almost loss, but of course he would have to flip a switch or get a remote controlled A-B switch from Radio Shack.

bix2 · Jul 21, 2008

Yes 300ohm I did point this out.

His requirements were different. The two antenna's were combined, and then split again for input to a HD network tuner. The use of high gain antenna's overcomes the feedline and combination loss, without the need for preamps.

The SiliconDust HDHomeRun tuner is located in a basement network closet. Both inputs of his network tuner see all HD channels. The tuner is attached to a gigabit network. Network video is available throughout the house.

Here's a link to the tuner specs:
/http://www.silicondust.com/wiki/products/hdhomerun

300ohm · Jul 25, 2008

An update on my snap on adjustable, one standoff fits all design.
To show how strong a fit it is, pictured it is holding a 30lb (13.6 kg) old cast iron compressor housing. No glue or screws are used anywhere, just push fitted, heh. Also pictured to the right is another 1/2 inch pvc tee cut (or sanded with a belt sander) along the outside to fit 1/4 inch by 1 inch aluminum bar stock. Only a sample piece is shown, but using a suitable length, a grid (fencing material) reflector can be attached easily. For sizes other than 1/4 inch bar stock, just sand enough of the pvc tee so the bar stock is flat even with the aluminum tube boom.
Besides the 7/8 inch OD (3/4 inch ID) aluminum tube, common 1/2 inch steel plumbing pipe is also 7/8 inch OD, but its much heavier.

and now my coax antenna lines are about 10' long instead of the 60 to 75 feet that they would have been otherwise.

You saved yourself about 2.3 - 3.05db in RG6 cable losses by doing that. Thats a lot.

ctgottapee · Jul 28, 2008

when constructing the DBGH...

would it be easier to use 300ohm antenna wire - the kind with the two wires in the vinyl jacket - to make the feeder lines? it seems like there might be more error involved bending heavy guage wire used for the elements, so i was thinking of just using the cable as i have some anyway.

i was going to run one cable as a feeder line connecting the two antennas, and then splice a second cable into the middle of the first one and run it to the preamp

----

i was also thinkiing of putting some small pieces of heat shrink tubing over the copper elements at the point they touch any screws holding the antenna together to help prevent corrosion unless that would affect the reception.

----

final question is on antenna spacing. i have a seperate vhf antenna and was wondering what is the closest distance i can have it on the same pole. was thinking of mounting it a few inches underneath the DBGH, 5 element yaggi 7inches long

300ohm · Jul 28, 2008

would it be easier to use 300ohm antenna wire - the kind with the two wires in the vinyl jacket - to make the feeder lines? it seems like there might be more error involved bending heavy guage wire used for the elements, so i was thinking of just using the cable as i have some anyway.

Using 300ohm wire will work, but the question is always how much it will affect performance. That hasnt been modeled yet. You want to maintain a consistant distance above the elements and thats almost impossible with plastic encased twin lead. Good phasing lines are very key to performance on the DBGH. I used open wire 300ohm twin lead on mine while I was readjusting the phasing lines, but thats completely different stuff. Also if using a feeder gap larger than the original plans, the phasing gap should be wider. Ive modeled my 88mm feed gap DBGH and will post the results of my phasing line spacing in a couple of days after some real world testing.

i was also thinkiing of putting some small pieces of heat shrink tubing over the copper elements at the point they touch any screws holding the antenna together to help prevent corrosion unless that would affect the reception.

If the heatshrink tubing doesnt slip, that will work. If it slips, the elements will turn defeating the purpose of screw. Oversize triangle homemade plexiglass/thick plastic washers are another easy option. Also dont insulate the electrical connection points.

final question is on antenna spacing. i have a seperate vhf antenna and was wondering what is the closest distance i can have it on the same pole. was thinking of mounting it a few inches underneath the DBGH, 5 element yaggi 7inches long

You mean 7 foot long, heh. It would be better if it were least a couple of feet apart, for the performance of both antennas.

300ohm · Jul 29, 2008

Ive had my SBGH as per my plans in my signature below up for a couple of weeks now for testing. Its amazing how fast new copper tarnishes on a roof, heh.

Its actually very sturdy with just that one chimney mount and doesnt wiggle much in a strong wind. Part of my 12 pair colinear rod DBGH is shown on the other side of the chimney.

And this SBGH definately feels like its following the model very very closely. I can really notice that drop off after channel 55, its significant. (when I made my first SBGH which eventually became that DBGH part of which is shown, it performed better on the higher frequencies than the model for reasons I have yet to explain. But Im happy that it does, as right now I need those channels in my NorthEast direction) Right now, this SBGH is pointed in the SSW direction so I get my Salisbury MD stations and I now get them all at 90% or better. For a while I had it in the Washington DC direction and was able to pull in DC stations from 80 miles away fairly consistantly. I have the antennas with separate RG6 cables coming into the house to an RF A-B switch for quick changing between them. I like this arrangement much better than a slow rotor.

Billiam · Jul 31, 2008

New Idea For SBGH and DBGH

My friend wanted me to throw out the following to the developers of this antenna to see what they think.

"There is one other item I'd like to suggest to them in their G-H designs- even though terrestrial TV is going away above ch. 51, there is a company that bought the rights to use channel 55 nationwide for some sort of mobile digital TV, IIRC. I'd appreciate it if they would redesign it so the gain wouldn't roll off til past channel 58* so anyone using these could also use it for this other service. Please pass this idea on to them."

Your thoughts?

300ohm · Aug 1, 2008

300ohm, thanks for the great plans! The only change I made was I used 3/4 pvc since I already had a few elbows and t's laying around.

Thanks, even though I got most of the ideas from DogT and WYSRTV9. The triangle plexiglass washers are my idea, though. Yeah, I figured about $25 if everything had to be purchased. 3/4 inch pipe and fittings will make it even more stiff, at more expense though. It still should be mounted to a sturdy mast, even though I havent done that to mine yet and it seems to be fine. Giving the pipe one coat of cheap flat (I use flat black so its less noticible to the eye, but the plumbing pvc association recommends a light color for longevity) spray paint will increase the life of the pvc pipe outdoors, just dont paint the elements (at least not at the electrical connection points).

300ohm · Aug 1, 2008

Your thoughts?

Generally, the smaller the total bandwidth, the greater the gain the antenna can be designed for. For specific uses, like what is being planned for the old uhf channels, a high gain yagi cut for that specific frequency would be best IMO.

Mobile TV by its nature is going to require an omnidirectional antenna or a smart antenna. (or a rotor that tracks the signal ?) As such, I expect the range to be limited.

GH for UHF (Plans, Parts Lists, Build Tips by 300ohm)

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