good info on radials/groundplane on yagi beams

[209 first class]

i had read the brownish orangish pipe layout thread, the consensus was that it wouldent make much difference. but the guy insisted there was performance increase with his beam. i had heard in the past ground systems/ radials mainly effect vertical antennas, and not really yagis/ beam antennas. in my ground snooping on the web last nite, i found some good stuff. YES the vertical antenna suffers greatly in efficiency over a poor ground, maybe up to only 25% of the power getting out, and they yagi beam suffers almost none of this efficiency loss. i wondered is this is why everyone says flat side works better than vertical with a beam?(excluding the noise factor). but what i never knew is that although it does not suffer from the efficiency loss, the yagi will suffer greatly in its angle of radiation if over poor ground. the radiation pattern will be higher in angle over poor ground. a good ground pulls the lobes toward earth into the shape they are supposed to be. i think that is why the brownish orangish pipe layout helped the performance, it lowered his angle of radiation more toward the horizon.(where the antennas are). my beam is at 38 feet, just a hair over one wavelength. unfortunatly that makes my angle of radiation higher than it should be. i knew that in the beginning, but i had a certain budget for the tower setup, and got the best i could. so, now i will be unwinding some old transformers to get the enamled wire to put in a ground radial system under the tower/beam. i will put a switch out there too, sometimes the higher angle may come in handy when skipping under 1000 miles, as the books say.i can try to note differences with and without the radial system. here is the link, i hope it works. i got this info from butternut, the tech notes. lots of reading, everything i said is in there somewhere. check it out http://www.bencher.com/pdf_do ... tech_notes

[209 first class]

whoops, correction: it says horizontal and vertical rf are affected differently, not the style /type of antenna. i assume its the same either way,and that a yagi could be affected both ways depending on how its oriented. just want to be clear. most of this is in the 'vertical antenna ad hype' tech note. 209

[209 first class]

here is a link with thorough explanation about why and how beam antennas perform differently vertically versus horizontally. http://www.cebik.com/yagi/vhp.html

[drdx]

I'll give that a read, but I was always lead to believe that grounding a yagi in the immediate area was of little or no benefit, and the ground plane that is in the fresnel zone, stretching something like 10 wavelengths from the base of the antenna, would be the area that effects performance. That area in most cases is one that you as an operator have no control over, unless you are on a big piece of land. That said, if the close up improvement of the ground does change the angle of radiation, that could be a good or bad thing depending on your goals. If you're a domestic ragchewer, or don't care about the UK, etc, then the lower angle would not help you and you would prefer the high angle. That UK, Japan, and Australia stuff sounds fun now, but after a while you just want to shout out to the boys over in the other part of the country. The lower angle would help on the ground wave part though. My further guess would be that the horizontal side would be least effected by the ground system changes. -drdx

[209 first class]

hi drdx, yes the whole thing was new to me too, i had heard ground effects dont really pertain to yagis. in the efficiency department this is true. vertical antenna efficiency is greatly affected by ground quality and height , but its angle of radiation is not. but with a yagi, efficiency is not really affected affected by the groundquality/height, but the angle of radiation is. im up to 21 1/4 wave radials, and 7 half wave radials around the base of the tower. its hard to make a judgement as im adding radials (first tried the 1/4 wave, then added the 1/2 wave ect.) and a on-off switch at the ground stake to make differentiation would ruin the good soldered connections. since i have lived here, all my antennas have been at 36-38 feet high. i mostly skip to the southeastern states. it is rare to get past texas,(i still have never talked to idaho, or utah, but ive talked to california, and washington/oregon) i hope for improvement although it will be hard to tell with out switching the radial system in and out. further reading tells me for optimum performance the radial system should be at least as far out from the tower base as it is tall. i also learned i will need at least 100-120 1/2 wave radials for an efficient radialsystem for low ground losses,(this is the requirement the fcc sets for commercial radio stations) but as my antenna is 38 feet high, i will need 120 38 ft (or longer) radials. wow, thats alot of c o p p er 209

[Popcorn501]

When i had my 6 elements up back in the day i had copper wire laid in the ground about 3 to 4 inches below surface 36ft long all around the base of the beam like a spider web.Now i didn't have no switch to cut it off and my tower was 50ft plus the pole coming out of the top i would say my beams where about 13 or 14 ft to the center.All of these ground wires where hooked to three ground rods then to the tower and i tell you what that set up was bad to the bone!!!! I run 900 watts into the beam and if there was any skip at all running i could talk to them with out any prob and cut alot of other people off that i couldn't here trying to talk.I'm not sure how much this help the beam but i believe it helped it a little bit.My ex brother-in law says he seen the beam take a direct hit of lighting one night didn't hurt anything.I think all the grounding had alot to do with that as well.Not sure if this is the kind of radials that you are talking about or not but just thought id share that with you.

[209 first class]

thats cool, sounds promising. its hard to spend money on all that copp er without being able to test the benefits for a cost/performance ratio, or, how good it works for the money. for instance a station with a stock mic might gain more performance with a nice 75$ powermic than i would from hundreds of dollars of coppe r in the ground, so far its a mystery . it would be nice to find an article on it on the web. 209

[Popcorn501]

I used mini8 coax shield for mine.

[DX47]

Yagis do not need a ground system of radials what so ever, they just need to be high up. A vertical, that is up high can get by with 3-4 radials, a 45 degree angle is the best for bringing the main lobe closer to the horizon.

Of course the tower your yagi is one needs to be grounded with ground rods. I have always thought it was good to put a rod or two when you dig the hole for the base and before the concrete goes in. I have heard that a lightning strike can crack the concrete if so, but I have never seen that personally.

A ground mounted vertical with radials is what is covered the most on the web, because a lot of hams will buy or build a vertical that is made for 10-80 meters. Since a quarter wave at 80 meters is around 60-66 feet they can't mount the verticals up on a tower or mast so they ground mount them and put down a lot of radials stapled right on the grass or bare copper wire in the earth itself. If they mounted them on a tower or mast, they would need to run many radials of different lengths to match each band, and the neighbors and the wife would not be happy with that... They say you can get a lot of performance from 8-16, 120 being the max. Verticals in this fashion are really made for DX, state short skip being not that great due to the angle of radiation. When radials are put in the ground, the actual lenght of them is not nearly as critical as when they are in the air.

I recently had a 40 meter dipole, then changed it to a 1/4 wave elevated ground plane with 4 radials. THe elements are 33 feet long, the base is 40 feet up and the top is at 70 feet or so suspended from a large tree branch that hangs out. I have 4 elements coming down at 45 degree angles. It is all made of wire, and man that thing is amazing!
It absolutly smokes the dipole which was horizontal. Before I only heard mostly state side, now I see Europe, Africa, Russia and the lower parts of South America every day.

For talking skip, a vertical does not really have to be that high at all, like a dipole... the driven element in a beam is a dipole. However, if you are one wave length up or higher, you should be good. It may be only 36-40 some feet to you, but it is a wave length and your lobes should be down lower than a beam that is sitting on top of the house. A vertical with a lot of radials can be lower and still talk a lot of DX, but you may not get a lot of luck around town with it. Around these parts the locals are idiots so it dosn't really matter

[209 first class]

i wasnt implying a yagi needed ground radials, the point of the info was the quality/conductivity of ground/earth affects the angle of radiation in a yagi beam. if your ground(meaning the earth around the base of the antenna) is poor, the angle will be higher than normal. a low angle of radiation will make a longer skip than a high one. 209