Full Wavelength Loop

[HomerBB]

Situation:

I have a full wavelength loop in my attic. SWR is good 1.4:1 in channel one, 1.1:1 on channel 40. It works fine, but is in the attic with the attendant impact on signal being there causes.

Thought:

I want to move it to the roof, but the roof line will bi-sect two of the quad shaped sides of the loop giving the loop two angled sides and two straight non-angled sides. The 5/12 pitch of the roof will give me about a 22.5* angle in those two sides.

Question:

Is this workable, and, if so, how might it affect the antenna.

The question is about expected performance due to being above the roof, and how the bending of the two sides might affect it's performance.

Currently it is mounted horizontally and fed from the corner matched with a 1/4^ 75ohm section to rg58U.

 

[C2]

i can't visualize the shape.

try it

 

[HomerBB]

i can't visualize the shape.

try it

crude, but may help:

fig. 1 is the current shape, but on the horizontal. As in fig. 2, it would drape across the roof line like a blanket.

 

[SR385]

The biggest performance hit you are taking is that people generally run vertical polarization...the difference if you talk to someone on a vertical is massive compared to talking to someone who is also running horizontal.

You would be better to put it up with wood or fiberglass masts on the gables and rope to tension it out so it would basically be a square or rectangle standing up on edge over the house, then feed it for vertical. If you bothered with that though, you may as well just make yourself a two-element quad and stick it up with a TV rotor on a mast.

 

[HomerBB]

The biggest performance hit you are taking is that people generally run vertical polarization...the difference if you talk to someone on a vertical is massive compared to talking to someone who is also running horizontal.

You would be better to put it up with wood or fiberglass masts on the gables and rope to tension it out so it would basically be a square or rectangle standing up on edge over the house, then feed it for vertical. If you bothered with that though, you may as well just make yourself a two-element quad and stick it up with a TV rotor on a mast.

I did make the quad (2 Element Quad), but I was looking for an omni antenna that wasn't in the attic and had a more stealthy profile. I am going to continue running the Quad, so I'll have two antennas. I am trying to keep the wife happy by not putting up two high profile antennas.

 

[W5LZ]

Actually, since that loop is at least close to a 'square' shape, and fed in one corner, you should have vertical polarization. If fed on the center of one side, it should be horizontal polarization.
If you could get the thing above the roof, not on the roof, the 'bends' on two sides shouldn't make a huge difference in radiation pattern. It being near the roof will have the most affect on the pattern because of the same attendant problems as if it were under the roof.
Horizontal loops have the same characteristics of other antenna with height above ground. Typically, higher is better, but almost any height more than about 1/4 wave length will work.
One way of looking at them is that the more area inside that loop, the more efficient they are, the less irregular the radiation pattern. That does not mean that an irregularly shaped loop won't work because they certainly will. It does mean that the less area inside that loop, the higher the input impedance will be. Carried to extreme, that could mean you end up with a folded dipole, sort of (which is exactly true, with all the attendant characteristics of same).
Getting that loop outside will make the largest difference in what you are hearing now (and the reciprocal, how they hear you). Getting it away from stuff nearby is also good. The further away the gooder. The larger that loop in relation to wave length (2 X, 3 X, whatever) and either keeping the shape the same or making opposite sides correspondingly/proportionally longer, will mean some increase in gain and some directivity especially with the thing positioned horizontal. Not exactly easy to turn, so figure it's a fixed directional antenna.
(I like loops, can you tell?)

They are not exactly cheap, and they do take some learning to make them things work, but an antenna modeling program is a very nice 'toy' to have. You do need to have some 'antenna smarts' to start with so that you know when the results are totally ridiculous, but that's not that hard to figure out. Try it, what's it gonna hurt, except your wallet, your ideas of what you thought you knew, your feelings cuz you thought you remembered some of that math stuff, and who knows what else? Ask me how I know, if you want, but I ain't telling anymore about that "who knows what else" @#$%!
- 'Doc

 

[C2]

WALTZ,

Why would the feedpoint matter on a horizontal loop? I remember that a vertical quad loop mattered as bottom fed made it an up and down thingy and fed on the side made it a left right thingy, or was it vice-versa??? And then there was the corner deal which was like bi-polaraized?

also, use a 1/4 wave 75-ohm piece of coax for a "Q" section matching device, which you can also coil to make a coax choke...

 

[Beetle]

How far above the roof are you going to have it? Do not just let it lie on the shingles or whatever. At low power it will suck up a lot of your signal. At higher power it will still suck up a lot of your signal, with the added possible benefit of an unplanned visit from the fire department...

If you can't get it at least a few feet above the roof, it would probably work just as well underneath the roof as it is now.

 

[HomerBB]

okay.
I take it that I need to get it as far from anything as possible.
I have it in the attic, getting it out of the attic alone will help.
It is suspended from four corners, and very nearly a perfect square. It is corner fed, and is suspended flat, not hanging like a curtain from one side. It is only one wavelength long at this time.
It is matched with a quarter ^l 75ohm match section.

I feared it would screw its radiation pattern up badly to drape it over the ridge of the roof. I wanted it to be non-directional, and vertically polarized.

What does it do when I place it on one side of the roof at the same pitch as the roof facing the west? directional? polarized horizontally or vertically? wonderful? worthless???

thanks, everyone.

 

[High Voltage Mobile NJ]

Situation:

I have a full wavelength loop in my attic. SWR is good 1.4:1 in channel one, 1.1:1 on channel 40. It works fine, but is in the attic with the attendant impact on signal being there causes.

Thought:

I want to move it to the roof, but the roof line will bi-sect two of the quad shaped sides of the loop giving the loop two angled sides and two straight non-angled sides. The 5/12 pitch of the roof will give me about a 22.5* angle in those two sides.

Question:

Is this workable, and, if so, how might it affect the antenna.

The question is about expected performance due to being above the roof, and how the bending of the two sides might affect it's performance.

Currently it is mounted horizontally and fed from the corner matched with a 1/4^ 75ohm section to rg58U.

what frequency are we talking about here ???????

 

[W5LZ]

What happens if you put it on one slope of the roof? Without being real definite about it, it'll make the radiation pattern sort of 'tend' in that direction. It would still be 'mostly' omni-directional, but would sort of 'tend in the direction of the tilt, not really, but almost like a 'slopper' would, sort of. Boy! That's really definite ain't it?
- 'Doc

 

[W5LZ]

Double post - sorry

 

[High Voltage Mobile NJ]

you guys need to first no what frequency your talking on !

 

[W5LZ]

High Voltage Mobile NJ,
Since this is a general question about an antenna, the frequency doesn't matter at this point since it wouldn't be changed.
- 'Doc

 

[C2]

k