dipole question

[522]

so lets say all things being equal.

dipole mounted horizontal
dipole mounted as an inverted "V"
dipole mounted with one leg up as an "L"

which one wins for local talk?
which one wins for DX talk?
which one wins for a compromise between the 3?

also, which one would benefit the most from a height advantage?

currently at 10 feet... wanna go to almost 30 feet. which antenna position will benefit most?

thanks !!

 

[Robb]

so lets say all things being equal.

dipole mounted horizontal
dipole mounted as an inverted "V"
dipole mounted with one leg up as an "L"

which one wins for local talk?
which one wins for DX talk?
which one wins for a compromise between the 3?

also, which one would benefit the most from a height advantage?

currently at 10 feet... wanna go to almost 30 feet. which antenna position will benefit most?

thanks !!

Mounted as an inverted 'V' it will still behave like horizontally polarized antenna - horizontal polarization. Mounted with one leg up will behave as a vertical antenna - vertical polarization.

Most people talk vertical locally, and either horizontal or vertical with DX.

Horizontal polarized antennas are directional; verticals are omni-directional.

And YOU thought it was going to be easy to choose.

Ha!

Mount it as high as you can safely - but 30 ft would be great.

 

[522]

well, i have very little local talk here... BUT, i live very close to 2 major interstates. i wouldn't mind being able to give local directions.

BUT ... i think id rather talk DX than talk to the local traffic.

 

[Needle Bender]

if you get it around a 1/2 wavelength above the ground or higher the inverted v should give you both horizontle and verticle in omnidirectional but not really great in iether. if you just want an antenna that will do everything in all directions then its the inverted v but you will need alot of power to be heard thru the skip because a inverted v is about 6db down from a 5/8

 

[W5LZ]

I'm afraid that inverted 'V' is still a horizontally polarized antenna until it's stood on end, it won't have any vertical polarization at all. And there's not '6 dB' difference between a 1/2 wave and a 5/8 wave antenna. There's something difference between a 1/2 wave and 5/8 wave in the 5/8 wave's favor, but only something around 1 or 2 dB. There can be something like 6 dB difference seen on an 'S' meter, but that's because of polarization, not 'gain'.
A dipole's polarization depends on it's orientation/positioning in relation to 'ground', or the dirt under it. 'Bending' it into a 'V' shape does certainly change it's impedance and the shape of it's radiation pattern characteristics, but not in relation to polarization. Height above ground/dirt also doesn't affect polarization, but can have a considerable affect on any antenna's impedance and radiation pattern.
It isn't always easy to keep the distinction between polarization and other characteristics separated and is easily misunderstood. The easiest way of changing polarization is by the antenna's orientation with earth, tilt the thing over 90 degrees. That tends to work with any type of antenna.
That first sentence, "so lets say all things being equal.", is the 'sticking point'. Typically 'things' aren't going to be 'equal', sort of. A horizontally polarized antenna can have beneficial performance when mixed with vertically polarized antennas at a distance (DX). But that's not always a fact, and deals with the changes possible when a signal 'skips', or 'bounces' because of propagation. That polarization change isn't a predetermined fact, it always depends on the state of propagation, how the signal 'bounces', and that's not very predictable at all. Just like 'flipping' a coin, you can't predict the outcome all the time (unless you cheat, of course). That doesn't mean that a vertical antenna is no good for DX, it certainly can be. It has the same chance as a horizontally polarized antenna, about 50% of the time.
So, diceide which/what you want the thing to be able to do, AND which/what would be most practical or convenient for you. No one get's it 'right' 100% of the time, so you've got as good a chance as anyone else does. Don't like the results? Who says you can't change it?
- 'Doc

 

[Beetle]

Set it up as a flattop first. Use it for a week or so and get to know it for yourself. Then change the configuration and leave it that way for another week and check it out. Keep doing that until you've found what works best for YOU.

 

[Needle Bender]

I'm afraid that inverted 'V' is still a horizontally polarized antenna until it's stood on end, it won't have any vertical polarization at all. And there's not '6 dB' difference between a 1/2 wave and a 5/8 wave antenna. There's something difference between a 1/2 wave and 5/8 wave in the 5/8 wave's favor, but only something around 1 or 2 dB. There can be something like 6 dB difference seen on an 'S' meter, but that's because of polarization, not 'gain'.
A dipole's polarization depends on it's orientation/positioning in relation to 'ground', or the dirt under it. 'Bending' it into a 'V' shape does certainly change it's impedance and the shape of it's radiation pattern characteristics, but not in relation to polarization. Height above ground/dirt also doesn't affect polarization, but can have a considerable affect on any antenna's impedance and radiation pattern.
It isn't always easy to keep the distinction between polarization and other characteristics separated and is easily misunderstood. The easiest way of changing polarization is by the antenna's orientation with earth, tilt the thing over 90 degrees. That tends to work with any type of antenna.
That first sentence, "so lets say all things being equal.", is the 'sticking point'. Typically 'things' aren't going to be 'equal', sort of. A horizontally polarized antenna can have beneficial performance when mixed with vertically polarized antennas at a distance (DX). But that's not always a fact, and deals with the changes possible when a signal 'skips', or 'bounces' because of propagation. That polarization change isn't a predetermined fact, it always depends on the state of propagation, how the signal 'bounces', and that's not very predictable at all. Just like 'flipping' a coin, you can't predict the outcome all the time (unless you cheat, of course). That doesn't mean that a vertical antenna is no good for DX, it certainly can be. It has the same chance as a horizontally polarized antenna, about 50% of the time.
So, diceide which/what you want the thing to be able to do, AND which/what would be most practical or convenient for you. No one get's it 'right' 100% of the time, so you've got as good a chance as anyone else does. Don't like the results? Who says you can't change it?
- 'Doc

i dont agree because ive seen one help with verticle performance when he droped the ends into a v and i found an interesting website that talks about it as a omni both verticle and horizontle with this model from eznec

 

[W5LZ]

Neither 'EzNec' nor any of the other antenna modeling programs can distinguish between vertical or horizontal polarization. I'm afraid that model only shows an omnidirectional pattern (no matter what the author says/claims). That model is for an 80 meter inverted 'V' at less than a 1/2 wave length above ground, it's also typical.
- 'Doc

 

[522]

im almost certain that i will try it horizontally at first, and just see how it goes. i can always change it later if i want to.

did i mention this will be on a flat roof ? anywho, it will be... one of my concerns will be snow. i get plenty of snow here in my area, and wondering if i dont get the antenna high up above the roof line, snow MAY cover up the antenna.

will this affect the antenna in any way shape or form? at least enough that i will notice ?

 

[Robb]

ON the roof; or ABOVE the roof?

 

[522]

i do NOT want the dipole laying flat on the roof.

my goal was to have it at least 2 feet ABOVE the roof. but still there is a good chance snow could cover it up at 2 feet.

 

[Beetle]

I had the same question as Robb: ON or ABOVE. Thanks for clearing that up! I actually asked the question on your other post about putting the mobile antenna on the roof with a tripod and some radials, but the forum doesn't seem to have picked my post up.

2 feet above the roof would seem to be okay, but is it completely "flat"? Sounds like an awful lot of weight from the snow.

As far as the question about the 102" whip, you'd undoubtedly find that it was too short and in need of a 5 or 6 inch extension. Then, with at least 4 radials, it should work pretty well. For the angle of the radials, your best bet would be to experiment and see what different angles get you.

 

[Robb]

Yup - what Beetle said.

You don't have to use a steel whip either for the vertical. 1/2 inch electrical conduit is cheap ($3 or $4 @ Lowes, Home Depot, etc) for a 10 ft length; just cut 1 ft off of the end and you have 108 inches/9 ft. That should be pretty close.

45 degree angle on the radials @ 108 inches each should also get you very close.
Trim the vertical for best SWR on ch 20.
Done

 

[Needle Bender]

Yup - what Beetle said.

You don't have to use a steel whip either for the vertical. 1/2 inch electrical conduit is cheap ($3 or $4 @ Lowes, Home Depot, etc) for a 10 ft length; just cut 1 ft off of the end and you have 108 inches/9 ft. That should be pretty close.

45 degree angle on the radials @ 108 inches each should also get you very close.
Trim the vertical for best SWR on ch 20.
Done

thats what i thought when i built one using 3/4inch copper tubing and 108inch radial wires on the roof but i had to keep cutting it until it was 8 feet 6 inches for 1:1swr on chaanel12 back when there were only 23 channel radios

 

[wavrider]

Like ROBB said it will get you in the ballpark.

Every installation is different, so every antenna will be tuned a little different.

EMT Conduit works great for elements. I have built several antennas using the 1/2" and 3/4" tubing. I even have a JO-GUNN home brew copy four element yagi made from 3/4" EMT tubing.

Can not beat the cost or the availability. Paint it to blend in with whatever environment you are installing it in and have fun for the vertical, use a dipole for the horizontal and you have the best of both worlds.

OH by the way make sure you wrap an rf choke AKA ugly balun at the feed point of the vertical if you do decide to build one.

Most of all have fun.