dipole question

[522]

i have been playing around with 2 different ideas. (one on this thread, and one on another thread)

102" whip as a base (with ground radials of course)
or, put a dipole on my roof.
whether the dipole was horizontal or vertical or inverted v or what, was undecided until today. i much prefer being flat. so that is my reasoning, and im going that route!

so now i need to homebrew a horizontal dipole. i am currently running a homebrew dipole made of speaker wire. works great ! just need some height, because the top of my 7 foot fence isnt cutting it. (again, back to the idea of putting it on the roof)

im putting it on my roof, which is flat and about 20 feet.
some wind, and a lot of snow are my main concerns. so i am thinking / hoping to make it relatively strong. i think 1/2" conduit is gonna be my best friend.

now i need to rethink how my "mount" is gonna work. i had an idea for the 102" attached to a homebrewed tripod. BUT now that the antenna will be horizontal, i kinda need to hit the drawing board again. shouldnt be too hard though.

plan is to have the dipole 2 - 3 feet above the roof line.
i have a rough drawing of what i had in mind for the mount. i will see if i cant post that up here soon.

also, any one with suggestions / tips , please feel free to post up.

thanks !

 

[Needle Bender]

remember a strait dipole is about 72ohms and 1.5 swrs so if you can bend it a little in the middle to about 125 degrees it will go flat on swrs when you trim it to the right length, about 8 foot 7 inches on each side. or yuou can use a gamma match amd keep it strait

 

[W5LZ]

I think you'll see an improvement in reception with the antenna on the roof. So, it would be worth doing just for that reason. But then you get into what will have to be done to get the thing situated on that roof, and that's not exactly simple. Two feet above that roof would work, but getting it higher above that roof will also simplify/improve the performance. IIRC you may get some snow, and getting the thing above that snow is a very good idea since it will affect the antenna. Doubling or tripling that height would be better, if possible.
Input impedance and SWR. The typical 'flat' dipole has an input impedance around 70 - 75 ohms and would mean an SWR of somewhere around 1.5:1, that's correct. But, that 1.5:1 isn't 'bad' at all. 'Drooping' the legs of that dipole a bit will lower that input impedance, also true, and a very common way/reason for using an 'inverted V' type antenna. I think making the antenna resonant is much more important than the usual SWR differences you see with dipoles. 'Obsessing' about SWR just isn't worth the trouble.
So, good luck
- 'Doc

 

[Needle Bender]

i have been playing around with 2 different ideas. (one on this thread, and one on another thread)

102" whip as a base (with ground radials of course)
or, put a dipole on my roof.
whether the dipole was horizontal or vertical or inverted v or what, was undecided until today. i much prefer being flat. so that is my reasoning, and im going that route!

so now i need to homebrew a horizontal dipole. i am currently running a homebrew dipole made of speaker wire. works great ! just need some height, because the top of my 7 foot fence isnt cutting it. (again, back to the idea of putting it on the roof)

im putting it on my roof, which is flat and about 20 feet.
some wind, and a lot of snow are my main concerns. so i am thinking / hoping to make it relatively strong. i think 1/2" conduit is gonna be my best friend.

now i need to rethink how my "mount" is gonna work. i had an idea for the 102" attached to a homebrewed tripod. BUT now that the antenna will be horizontal, i kinda need to hit the drawing board again. shouldnt be too hard though.

plan is to have the dipole 2 - 3 feet above the roof line.
i have a rough drawing of what i had in mind for the mount. i will see if i cant post that up here soon.

also, any one with suggestions / tips , please feel free to post up.

thanks !

i just rememberd another trick i heard while litsening to the ham bands. if you make a strait or flat dipole way too long so it goes right to 2 to 1 swr for 100 ohms then cut a 1/4 wave of 75 ohm coax using the velosity factor and put it right at the antenna with a barrel conector to your regular 50 ohm coax your suposed to get a little gain but have flat 1 to 1 swrs
i wonder if a gainmaster on its side would give much horizontal gain?

 

[W5LZ]

"...wonder if a gainmaster on its side would give much horizontal gain?"

Easy to answer. Just turn one on it's side and you'll find that it has the same gain as it had before but horizontally polarized.
As for the other idea, if you position the thing so that one of the lobes produced by that difference in length is pointed in the right direction, it would produce some gain. The 'catch' to that is that there will also be nulls in it's directional pattern, which means that it will have a loss of gain in some directions. Who knows if you've got it 'pointed' in the right direction? And then, if you extend that double's length far enough you won't even need that matching section of 75 ohm coax. The input impedance will come down to 50 ohms all by it's self. The 'catch' to that idea is that the radiation patter, where it ends up putting a signal, isn't dependent on SWR at all and the thing won't be very effective/efficient an antenna because of resonance. SWR doesn't tell you anything about how well an antenna works, only how well impedances are matched. Which is only one part of tuning an antenna.
- 'Doc

 

[gamegetter]

futile ?

sometimes it seems that efforts are useless. i see the impedence (match)and resonance (tune)explanations over and over.

Properly matching the antenna impedance to the line impedance is important. There are many, many articles out there about antenna impedence matching. Failure to arrive at a decent match can lead to transmitter or amp failures but more often just plain inefficiencies.

Knowing the resonance point is important in achieving the match. Does not have to be exactly tuned to match but starting out with a resonant antenna on frequency you intend to operate on is a good way to end up with a better tuned, matched and efficient system.

I think the problem with understanding this has been that antenna manufactures have used the "lengthen or shorten" method to explain to customers how to tune or match and have used the words tune and match synonymously for many many years.

Hope this helps a little

 

[gamegetter]

needlebender:

as to taking a gm and installing it horizontal, yeah it should work and as mentioned no there will probably not be any more gain.

why spend 200 bucks when you can make a horizontal dipole for much cheaper, 1/2 wave maybe slightly less gain than a 5/8 which can be made in an extended zepp. there are several other horizontal wire antennas with gain, look up N4GG.

I think you may have missed the explanation on the GM thread regarding why a sophisticated antenna was built to take the horizontal 5/8 wave dipole into the vertical orientation. I would refer you to reread that and perhaps do some research in trying to under stand the matching problems of doing above. We see this matching issue with many of the 1/2 wave vertical antennas on the market today.

Well have to go but perhaps this will help a bit.

 

[Captain Kilowatt]

I think the problem with understanding this has been that antenna manufactures have used the "lengthen or shorten" method to explain to customers how to tune or match and have used the words tune and match synonymously for many many years.

Hope this helps a little

That is true. When you tune an antenna you are looking for the point where you have zero reactance at the frequency you want to operate on however that point may not present 50 ohms of pure resistance. Matching is when you transform that resistance, whatever it may be, to 50 ohms. Most people tend to confuse resonance with a low SWR but I have had resonant antenna that were as low as 5 ohms and as high as 200 ohms yet they were perfectly tuned. They had zero reactance but still had to be matched to the 50 ohms my transmitter was looking to see.

 

[Robb]

i just rememberd another trick i heard while litsening to the ham bands. if you make a strait or flat dipole way too long so it goes right to 2 to 1 swr for 100 ohms then cut a 1/4 wave of 75 ohm coax using the velosity factor and put it right at the antenna with a barrel conector to your regular 50 ohm coax your suposed to get a little gain but have flat 1 to 1 swrs
i wonder if a gainmaster on its side would give much horizontal gain?

Are you saying to cut the dipole to a 5/8 wavelength and then tune the impedance so it can behave like a horizontal GainMaster?

Impedance would be an issue - unless a gamma match or a tuning stub was used.

Thoughts?

 

[Needle Bender]

Are you saying to cut the dipole to a 5/8 wavelength and then tune the impedance so it can behave like a horizontal GainMaster?

Impedance would be an issue - unless a gamma match or a tuning stub was used.

Thoughts?

i think thats why they said to use the 1/4 wave of 75ohm coax. i think it works to match it and to tune it. i wish i had written down his call sign but he said he was getting better performance from it then when it was cut for resonence but it wasnt 5/8 long on each side just long enough to reach 2 to 1 swr before he added the 75ohm 1/4 wave.
on the gainmaster i was wondering if the gain it gets on verticle would be even more on horizontle because of ground gain and if it would beat a normal 1/2 wave dipole enough to be worth it plus it would be more convenient for some who dont have two places to mount the wire dipole from

 

[KASZ 9113]

I'd have to agree with Needle Bender on this one. An inverted V dipole with the leads at 90 degrees will give you a horizontal and a vertically polarized dipole. Should be at least 28 feet of the ground. I hear also of having to run the coax at 90 degree angles from the antenna, but I have never experienced any "loss" by not doing so. My late father was a radio man in WWII in the Marine Corp and suggested I look to the USMC manuals as they used dipoles a whole lot back then. Goggle up the USMC MCRP 6-22D USMC Field Antenna Handbook and read the whole thing. It's a great read with many different "improvised" antennas. Plus it has alot of important antenna theory. Then check out www.k&mem.150m.com. It's an inverted V worksheet to plug in all your info and it does everything for you. All I use is an inverted V with about 1200 whiskeys and have no problem talking skip when Mother Nature lets me. It's not a beam or a high dollar ground plane, but it is low buck, high adventure. I have about $30 into mine. It will do just fine for me until I can afford to get my Enforcer. Just remember, inverted V's need to be up there and power to really get out.

 

[Needle Bender]

hey kasz9113 you accidently hit shift when you hit the 7. its k7mem for a free yagi design program
have you thought of adding some 1/2 waves at each end of your 1/2 wave dipole with a shorted 1/4 wave long stub of 450 ohm hanging down phaze coupling each one? now i bet that would give you some gain if you added two more 1/2 waves or even 4 more, two on each end.
since you start out with a 1/2 wave dipole then double it for 2.14db, then double that for another 2.14db i bet you would get about 5db gain with 5 total 1/2 waves or about 45 feet on each side with two aditional 1/2 waves and two stubs on each side
thats almost a million db joe gun audio gain

 

[wavrider]

N4GG is a vertical Array not a Horizontal array, it uses 1/2 wl of horizontal wire to phase the verticals together, In reality it is a 3.2 dipole with the last 1/4 wl hanging vertical, no magic here. As we all know a 3/4 WL conductor has the same impedance as a 1/4 wl conductor.

The Lazy H is a phased array of dipoles, it can be constructed as a mono bander using coax to feed it and a tuning stub, or feed with ladder line and a coupler used in the shack. Works great.

 

[W5LZ]

Sounds good, doesn't it? Unfortunately, it just don't work that way.
There are horizontal arrays as well as vertical arrays. Basically just two or more 'elements/antennas' connected by a phasing device (network/lines). And yes, they do produce 'gain' in particular directions.
That '2.14 dB' would be better stated as '2.14 dBi', which is the typical difference between 'real' and 'isotropic' gain, the isotropic gain being '2.14' larger than the 'real' gain. After that, that '2.14' has no particular significance with anything.
Tell 'Jogunn' about all that! I'm sure they will figure a way to work it into their advertising...
- 'Doc

 

[Needle Bender]

Sounds good, doesn't it? Unfortunately, it just don't work that way.
There are horizontal arrays as well as vertical arrays. Basically just two or more 'elements/antennas' connected by a phasing device (network/lines). And yes, they do produce 'gain' in particular directions.
That '2.14 dB' would be better stated as '2.14 dBi', which is the typical difference between 'real' and 'isotropic' gain, the isotropic gain being '2.14' larger than the 'real' gain. After that, that '2.14' has no particular significance with anything.
Tell 'Jogunn' about all that! I'm sure they will figure a way to work it into their advertising...
- 'Doc

i was talking about gain in the real world over his dipole not isotropic gain. i was using a chart i found at the bottom of the page here but it is 2.15 not 2.14. my bad