 Notice. New forum software under development. It's going to miss a few functions and look a bit ugly for a while, but I'm working on it full time now as the old forum was too unstable. Couple days, all good. If you notice any issues, please contact me. |
Forum Index : Other Stuff : NextG Yagi aerial.
  Page 2 of 2 |
|||||
| Author | Message | ||||
wallablack Senior Member  Joined: 10/08/2011 Location: AustraliaPosts: 164 |
Does anyone know if these types of home-brew Yagis benefit from a reflector on the back like the commonly purchased one like below? The one I am looking at building doesn't have one and it seems not a lot of DIY ones do. 
Foolproof systems do not take into account the ingenuity of fools. |
||||
Gizmo Admin Group  Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
I dont think so. It may even make things worse if you dont get it right. On that original design the last big element behind the feed elements is the reflector anyway, and its designed to reflect a narrow bandwidth forward into the feed elements. Get it wrong and you could screw up the tuning. You could try it, but only once you have a working YAGI and some dbm figures. Bit of a black science really. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
| MOBI Guru  Joined: 02/12/2012 Location: AustraliaPosts: 819 |
The reflector doesn't have to be a grid type as in your picture, but a single rod reflector a bit bigger than the driven element and about the same distance from the driven element (opposite side to the directors)as the directors would benefit. I'm sure you look up the net, you will find design figures for Yagi antennae. I am surprised that reflectors of either sort are not used. The reflector acts just as its name and the directors (the saw fish looking elements)act as convex lenses to focus the signal. The design criteria are probably in my old ARRL Ham handbook. I'll see if I can find it. I have been getting rid of things I no longer use. Nostalgia and sentimentality is cluttering. David M. |
||||
powerednut Senior Member Joined: 09/12/2009 Location: AustraliaPosts: 221 |
Yeah, the element behind the driven element in the pictures is the reflector. The gain difference between using a mesh reflector and the single reflector can be reasonably high - certainly worth experimenting with. I think I recall it can be around 6db, assuming you have everything spaced correctly. ARRL Antenna book is definately worth getting if your going to be experimenting with them. Mine is the 17th edition (1994), so getting just a little bit dated. |
||||
| wallablack Senior Member Joined: 10/08/2011 Location: AustraliaPosts: 164 |
The one I am building is from HERE It seems to me that this guy has built a reasonably good one and for an $40 outlay it will be a good project. I could have used scrap from home but chose to buy 10mm aluminium tube from Bunnings for a mere $2/metre. The elements look like this: 
Foolproof systems do not take into account the ingenuity of fools. |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
Glenn, I built the same one and the alu tubes were from an old TV aerial. Even in the city where an omnidirectional whip is better I am getting two to three more bars. Other interesting concoctions are those wok aerials where the wok is a kind of parabolic dish and the USB NextG dongle is placed into the focus. How do you get your aerial cable into the house without inviting flies thru the open door? Is your whip your highest metallic point on the roof and was this the reason for taking it down all the time? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
| wallablack Senior Member Joined: 10/08/2011 Location: AustraliaPosts: 164 |
I hope you all had a great Christmas with your family!!! Question: I have a Testra 3G tower on a hill which is about 2Km as the crow flies. This hill is 50m above my house. I was going to point this YAGI at the tower but I have read that the signal produced from this tower will probably shoot right over the house and it will be pointless. My next 3G tower is 20Km as the crow flies. Has anyone tried to point these things to an "uphill" tower or would it be a waste of time? I have connected the DIY YAGI today and pointed it to the 20Km away tower with a slight increase in "bars"....Hard to tell as it bounces between 2 and 3 bars all of the time. Foolproof systems do not take into account the ingenuity of fools. |
||||
| Gizmo Admin Group Joined: 05/06/2004 Location: AustraliaPosts: 5078 |
Hard to say, try pointing at the close tower and see how it goes. Signal strenght is a "ok" indicator, but a data speed test is better. I've had situations where moving the aerial off to one side gave less signal strength, but increased data speed. My last 3G yagi was pointed at a dirty great hill, and gave the best speed. At the end of the day, its data speed that counts. I use http://www.speedtest.net/ to get an idea of download speeds while turning the yagi. Also you may need to try different polarizations. 3G towers can be vertical, horizontal or 45 degrees, depends on what they have to compete with in the area. Glenn The best time to plant a tree was twenty years ago, the second best time is right now. JAQ |
||||
Prime_8 Regular Member  Joined: 07/12/2014 Location: CanadaPosts: 51 |
wow , great stuff . been ages since i have see nice home-built antennae(sp?) ~~ noise/on ~~ I ran a radioshack for few years and for the longest time I watched the real antenna parts stock drop . the demand was simply dropping to low for me to bring replacement in . do wet trees muck up the signal? ( muck == divert , bend , scatter , ghost ) In the early satellite TV days for Canada , i would be out installing dishes , only to find fir trees when wet would scatter signal and have you tracing false solids . Evene why by eye you know you had line of sight to the orbit you wanted , usually one of the Anik satellites. you could spend a hour to get the highest signal , only to see quality at 0 . It got to the point that i would go out to trouble sites and only de re aims on rainy days . LOL. DFI .. Douglas fir interference , upgraded to WDFI , Wet DFI . LOL ~~ noise/off ~~ way cool stuff , i take my wifi for granted for sure. Old coder, and bodger of things that may spark. |
||||
| domwild Guru Joined: 16/12/2005 Location: AustraliaPosts: 873 |
wallablack, From my little knowledge a Yagi is a directional antenna, while a whip is omnidirectional. Wouldn't you have problems with a Yagi in your area as the towers sometimes switch around depending on load? Taxation as a means of achieving prosperity is like a man standing inside a bucket trying to lift himself up. Winston Churchill |
||||
| Page 2 of 2 |
|||||
 Print this page |
