Mesh reflectors for antennas

[CincinnatiBob]

If you build an original SBGH (to the dimensions shown at http://www.digitalhome.ca/ota/superantenna/design.htm ) with a mesh reflector instead of a rod reflector:
1. How far behind the plane of the driven elements should the mesh reflector be placed?
2. Compared to the horizontal and vertical distances between the stub ends of the active elements, how wide and tall should the mesh reflector be?
3. If driven element spacing is widened just enough to increase the feed point spacing from 44 to 89mm how would that affect the answer to 2.?
4. In terms of signal performance, can a reflector be too tall or too wide?
5. Adding rod reflectors to a naked SBGH causes a narrowing of the beam angle. How much more or less does a mesh reflector narrow the beam angle?
6. Some recommend cutting a 1"-wide vertical slot down the center of a mesh reflector. How much does that affect performance and why?
7. Strength and durability considerations aside, what mesh parameters are likely to give the best performance (wire diameter, vertical pitch, horizontal pitch, cell shape)?

[300ohm]

Plans for the mesh reflector models are here, in the sticky : http://www.digitalhome.ca/forum/showthread.php?t=95898

[300ohm]

4. In terms of signal performance, can a reflector be too tall or too wide?

At wifi frequencies, yes. On the other hand, some people have gotten fantastic performance with uhf antennas near metal sided houses/buildings.

How much more or less does a mesh reflector narrow the beam angle?

There is a bit more gain with the orig GH and orig GH10 mesh models over the colinear rod versions of those antennas. With more gain, you generally get a narrower beam pattern. (but in this case, it will just be a little bit)

Some recommend cutting a 1"-wide vertical slot down the center of a mesh reflector. How much does that affect performance and why?

You get about .75 dbi more in gain for free. The GH design just likes split reflectors better, whether colinear rods or mesh. A tip, cut the gap last.

7. Strength and durability considerations aside, what mesh parameters are likely to give the best performance (wire diameter, vertical pitch, horizontal pitch, cell shape)?

You want to take into consideration wind load too. Common 2" X 4" mesh works well with minimum wind load. 14 to 16 gauge is what is commonly available. If you want about a db more gain on channels above 40, go with a 1" X 2" mesh. But strengthen the mast.

1. How far behind the plane of the driven elements should the mesh reflector be placed?

100mm, (plus 15mm or minus 5mm tolerance) same as the colinear rod version.

2. Compared to the horizontal and vertical distances between the stub ends of the active elements, how wide and tall should the mesh reflector be?

30 X 40 inches on the orig SBGH mesh version works fine.

[avenger]

I am fairly new to this forum. I built an original SBGH and it is located about 5 foot above the roof line. I am getting fairly good reception on all available local channels within a 45 miles radius, how would it affect the performance of the antenna if I attach a mesh backing to the original antenna's reflectors?. Would it degrade or improve the antenna's reception?.

Any advice or help is greatly apprceciated. Thanking you in advance.
avenger.

[300ohm]

Would it degrade or improve the antenna's reception?.

You would mostly see a little more signal on the meter on channels above 40.

[avenger]

Thank you for your reply. I will proceed in doing the addition of the mesh as soon as possible. At the present it is raining very hard at my area, as soon as the rain stops, it will be full speed ahead. Thanks again.

[mdbjorklund]

Hi, I am building another GH antenna and I want to determine the optimum material to use for the reflector. Here's my info from TV Fool: http://www.tvfool.com/?option=com_wr...bc2702b9adc241

I had good results with my first build: http://picasaweb.google.com/lh/photo...eat=directlink

but I feel like the mesh I used catches to much wind and hurts reception stability on blustery days. I would like to know if a reflector is even necessary. I also am considering trying the build style I saw from Windy's adjustable SBGH, but feel like his post for that design is lacking specifics (dimensions, etc.) any suggestions?

Also the 2x4 I see people using, I can't find a local source for that other than buying a 50ft roll for about $40...

[300ohm]

Also the 2x4 I see people using, I can't find a local source for that other than buying a 50ft roll for about $40...

2" X 3" is also common and will work the same as 2" X 4" if oriented the same way, but generally its a bit thinner gauge fencing, which is OK too if its flattened.

I would like to know if a reflector is even necessary.

In your case, you may be able to get most of the stations above 19.9 NM with no reflector on the DBGH. Just remove that fine mesh on the pictured DBGH and give it a try.

[mdbjorklund]

I only have it connected as a single right now. when I tried joining both elements (I only had enough 1/4" mesh for one half) my results worsened. I would like to accomplish two things with the next build.
1) stabilize the antenna by less wind resistence and maybe stiffer materials (ie. 3/4" vs. 1/2") and
2) get a usable signal on KCTS 9 (Seattle PBS) which I can't get now.
Would chicken wire work?

[300ohm]

Would chicken wire work?

Yeah, but 1" chicken wire is only equal to 2" X 4" mesh in performance, but with a lot more wind resistance. Larger poultry wire has way less performance. Also, you should put in the 1" vertical slit in the reflector for a bit more gain.

[Nolan Jinx]

Has anybody tried adding Hardware Cloth (half inch welded light wire mesh) to the back of (say) a Channel Master 4228HD or other brand to try and increase the reflection (range) of the antenna?

If so, what where the results?

My thinking is that by doing this you could make one of those cheap bow-tie antenna actually a decent buy.

Thanks

[stampeder]

Hello Nolan Jinx, that's a good question and generally it is a given that hardware cloth is only suitable for indoor use since it acts as a sail outdoors, meaning that a stiff wind could take your antenna down!

[M e]

Hello Nolan Jinx, that's a good question and generally it is a given that hardware cloth is only suitable for indoor use since it acts as a sail outdoors, meaning that a stiff wind could take your antenna down!

You say hardware cloth "is only suitable for indoor use" as a reflector (I assume)! Then what's the difference between the 1" x 2" galvanized steel hardware cloth and the 1" x 2" galvanized steel reflector used by the old cm4228?

Yes, a higher density mesh will have a higher wind loading. But IMO if 1" x 2" mesh was good enough for the cm4228 for years then it is still good as an outdoor reflector now.

[300ohm]

Yes, a higher density mesh will have a higher wind loading. But IMO if 1" x 2" mesh was good enough for the cm4228 for years then it is still good as an outdoor reflector now.

Yes, 1" X 2" mesh is fine, but its not considered hardware cloth. For the new channel range up to channel 51, about 1 1/2" X 2 1/2" mesh would be about the same as 1" X 2" mesh for channel 69 with less wind/snow load.

Hardware cloth, rat wire, is that thin metal stuff that is commonly sold in 1/2" X 1/2" or 1/4" X 1/4" sizes. 1" X 2" mesh is generally used for fencing and is thicker gauge.

[stampeder]

Reflector mesh is covered extensively in a variety of threads here in the Antenna Research & Development forum, so using the Search This Forum tool with the term "mesh" and other related terms will give a ton of good results. Try it with "hardware cloth".