The drawings for the GH show a 100mm dimension between the colinear reflectors and the element array. Is this dimension from edge to edge or centre to centre? If you're using #10 wire it's no big deal but if you're using 3/8" or 1/2" tube for the reflectors it makes a bigger difference. I will be using 3/16" aluminum solid rod for both. I assume this will be fine? The difference between edge to edge and centre to centre with 3/16" is almost 5mm which is 5% of the dimension. Which do I use?

okmed,

I used edge to edge spacing, meaning the distance of free air between metal. Read back to around pages 5 - 10 in this thread and youll see a graph of reflector spacing performance and further on a graph of element spacing.

Also I took edge to edge spacing for the element gap.

3/16 solid aluminum rod will make a very nice element. Also, you may want to flatten the aluminum at the bends with hammer and anvil because it will rise up by bending.

For the reflectors, I went with 3/8 inch aluminum tubing for the extra stiffness.

300ohm, where did you find 3/16 aluminum rods long enough? The longest I can find is at HD and they max out at, I think, 3 feet. The specs call for something between 4.5 feet for the elements when converted from mm.

Thanks in advance,
falcon

Here are pics of my quick SBGH prototype. Kind of messy and its hard to see the elements due to the aluminim reflector.

http://www3.sympatico.ca/mark.hermonat/ghside.jpg

http://www3.sympatico.ca/mark.hermonat/ghhead-on.jpg

Just standing it up in my bedroon pointing southwest (not optimized in location or rotation), the scan picked up 22 channels - the most I've had, even with my two bowtie combo in the attic. I am picking up CHCH (E!) and CTS with this one. Going to ramp it up to a better setup and try replacing my southwest-facing attic bowtie with this one to assess if its a true improvement. But initially the SBGH performs very well.

300ohm, where did you find 3/16 aluminum rods long enough? The longest I can find is at HD and they max out at, I think, 3 feet. The specs call for something between 4.5 feet for the elements when converted from mm.


I had thick aluminum grounding wire from a long time ago. (Ill have to search around for some more) The 3/8 inch tubing comes from old VHF antennas. Junk metal scrap yards are another good source of unusual size metals and types for very reasonable prices.

Yeah, you need about 60 inches per element in total. 3 foot of 3/16 inch aluminum would work fine, using 2 pieces for each element. Youll need a total of 4 pieces for the 2 elements of the SBGH. Then I would flatten the aluminum on the ends with hammer and anvil to about 3/32 inch, drill a hole in the flattened ends, bolt and 2 nuts each and that would be the center connection point for the downlead.

(when I say anvil, I mean any heavy flat piece of iron to function as an anvil. Aluminum and copper flatten very easily.)

...using 2 pieces for each element.

Ahhh yes - break each element into two sections. Smart. That makes sense. Thanks for the advice.

Falcon1987, I got the solid 3/16" aluminum rod from Metal Supermarkets and got them in 12 foot lengths. There's one near you in Oakville at 1290 Speers Rd. between 3rd and 4th Line.

Thanks okmed - looks like there is one in mississauga too. Will check them out.

This is my second antenna built to specs. It works better than the DBGH I built before because I added the reflector. I am able to pick up other channels that I couldn't before with the DBGH. I picked up some digital channels with about 50% strength and 60 miles way. My antenna is in the attic.

http://i31.tinypic.com/wgp5as.jpg

http://i29.tinypic.com/2469zcw.jpg

I think we should have a sub thread so people can post their GH antennas.

...because I added the reflector

Eraser88, what is your reflector made of?

The reflector made of reinforced concrete wire 5/32" thick. It's the same size as the zig zag.

I'm assuming that with a solid backing + aluminum foil reflector, one doesn't need to add the co-linear rods too? Is that correct?

That is correct, it takes its place.

I would smooth out the foil so its nice and flat, no higher than 1mm creases.

How critical is the antenna-to-reflector distance?

(I really should set up NEC so I can answer the question myself. But my free time keeps getting spent elsewhere.)

How critical is the antenna-to-reflector distance?


Look back in this thread (somewhere between pages 5 and 14 IIRC) for a graph of the DBGH Pair Reflector Spacing graph from 85mm to 115mm which Autofils did. At channel 46, 85mm was almost .5 db higher than 115mm. However, at channel 14, the 115mm looks to be .125db higher.

Finally got the DBGH put together and up at my niece's place this past weekend. Location is Merritville near the Welland canal and Glenview. Mounted it on a chimney mount on a two story home. Set it up facing Buffalo and get everything really strong including Global at about 60% if I remember correctly. Had to choose between CHCH or WGZR (no rotator so they can't get both), they chose WGZR.

The attached pictures show the construction. The backbone is 1" square aluminum tubing. The array elements and reflectors are solid 3/16" aluminum rod. I used 1/2" CPVC pipe and 10-24 threaded rod and some scrap 1/4" yellow plastic board for the array stand offs. For the collinear reflectors I drilled 3/4" holes through the square tubing and filled the holes with 3/4" wooden dowels cut to 2-3/4" and centre drilled to accept the 3/16" reflector rods and maintain the 20mm spacing. To keep them centered in the square tubing I cut 3/4" PVC irrigation nipples into 7/8" lengths with a hole in the middle for a #8 x 1/2" self-tapping screw to secure it and also help grip the rod with its point.

Not shown in the pictures is some sealant/adheasive that was smeared over the ends of the wooden dowels to protect the wood form the weather and also help hold the reflector rods in place (they are a tight fit and had to be hammered in). Also replaced the balun with a proper one that doesn't spring the copper wire together as it is in the picture.

http://i296.photobucket.com/albums/mm192/Okmed_bucket/P1000274.jpg

http://i296.photobucket.com/albums/mm192/Okmed_bucket/P1000279.jpg

http://i296.photobucket.com/albums/mm192/Okmed_bucket/P1000282.jpg

Nice build okmed. And some nice ideas in your build.

I think you may have misread the DBGH phasing line drawing. If you notice on the drawing, the feed spacing distance on the main length of the phasing line is 20mm. (I assume to maintain 300 ohm impedence, general rule 6 X the wire diameter) The element feed gap on each of the SBGH are 44mm (88mm - 95mm on the later discussions) but then the two phasing wires go together until 20mm spacing, then they go up until 30mm above the elements, then go straight down to the other SBGH section and repeat the above bends. As a general rule, the bends shouldnt be made too sharp.

Its easy enough to correct, and although (AFAIK) the phasing line hasnt been modeled yet, I think youll probably get a couple of more db in gain than the way you have it presently. ;)

http://www.digitalhome.ca/ota/superantenna/HovermanDimensions-2.jpg

DOH! I switched sides for the phasing lines by mistake.
Thanks 300ohm for pointing that out to me, although it doesn't seem to be hurting the performance any.
The phasing lines are the same #10 copper wire used on our 2 x 4 test mockup and when I put them on the final version I put them on the wrong side so instead of kicking back towards each other to maintain the 20mm gap they kick out away from each other to 68mm. Actually more like 72mm because back in post #344 I asked about compensating for the spacing dimensions if using 1/4" diameter tubing or larger and you suggested using the dimensions from edge to edge. My elements are 3/16" which is almost 5mm, hence the resulting 72mm spacing. I should have realized that with the bow in the phasing lines due to the tight leads on the balun. When one of the wires broke off I soldered a new balun on with longer leads so at least the phasing lines are parrallel, albiet too widely spaced. If it ever has to come down for any reason I'll correct it then but it's working too well to worry about it for now.
Thanks again for pointing it out though.

DOH! I switched sides for the phasing lines by mistake.


Heh, yep. I didnt notice that in the top picture when I first looked at it, but I did think the phasing line was even more to the outside than just going down straight. :D

Yeah, if its working well enough for her, no sense in risking a climb back up on the roof of a two story house.

The 3/16 inch solid aluminum rod elements ought to work out real nicely.

For comparison purposes I had my nieces husband check signal strengths at about noon today and then I immediately checked signal strengths at my location. We both have the same TV (Panasonic TH50PZ700U), he has the DBGH we built shown in post #375 with no rotator, chimney mounted on a two story home in Merriton near Glendale Ave and the Welland Canal.

I have a CM4228 with a rotator (but for comparison purposes made the tests with the antenna in the one position I would use if I had no rotator, pointing in roughly the same direction he's pointing) chimney mounted on a backsplit home in Port Dalhousie across the street from the lake. If you know St. Catharines that puts him about two Seaway Locks in elevation above me. Here are the readings:Channel-----Merriton-----Port Dalhousie
2-1.........58%............53%
4-1.........87%............68%
5-1.........92%............34 to 48% breaking up
7-1........100%............63%
9-1.........86%............71%
11-1..........0%............77%
17-1........100%...........100%
23-1........100%............86%
25-1.........58%............36% to 45% breaking up
29-1.........92%............60%
35-1.........46%............73%
36-1..........0%............69%
49-1.........69%.............9% no lock
65-1.........80%.............0%
66-1.........73%.............0%Hope you find this useful.

So hes on the escarpment, and youre down by the lake ? (The only thing I know about St Catherines is that I pass thru it on the way to Hamilton.) That would make for a pretty big difference in reception just for that increase in elevation.

Looking at TVFool for St. Catherines coordinates, 43.10N 79.14 W, your niece could do fantastic with a rotor. 21 maybe 25 stations, with all their subchannels, for probably well over 35 channels, very easily.