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Antenna polarization

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#1
I believe these two antennas are for 2 meters and 440.
(I'm not sure, but I believe they both would be called 2-element folded dipoles).
Any thoughts on if they are omnidirectional, or directional?
Thanks.
 

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#2
Depends on their exact design and mounting configuration. As you can see on the patterns in the link below, if you mount it one way, you get an omnidirectional pattern and another way a more directional pattern. Note that this directional pattern isn't nearly like a yagi where you get nearly all signal going in one direction, but more like a semi-omnidirectional pattern because of the interaction between the mounting tower and antenna.

My guess would be those in question are generally pretty omnidirectional in nature although there may be some interaction between the mounting pole (and other nearby antennas & mounts) that may distort the pattern somewhat. A more Omni pattern might be had by mounting each of the elements on opposite sides of the pole, assuming that their exact design would take that into account. That said, the distance between the elements and mounting pole may be enough to nearly eliminate the interaction between them.

http://www.commscope.com/catalog/doc/pdf/10461/Broadband_Antennas_Omni_or_Elliptical_Pattern.pdf
 
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#4
The larger (VHF?) dipoles look like Telewave brand and adjusted for either 3/8 or 1/2 wavelength from the mast giving either a cardioid pattern away from the mast or a bi-directional pattern between the dipoles and mast. See:http://www.telewave.com/products/antennas/pdfs/TWDS-7057.pdf

The smaller UHF dipoles appear to be a typical 1/8 to 1/4 wavelength spacing giving a directional pattern away from the mast.
prcguy
 
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#5
Those are simple 2-bay colinear arrays, slight gain. They are ideally omnidirectional in the horizontal plane but oblong in the vertical plane, that is they have some gain out toward the horizon. Antenna gain is achieved by stealing power from one area and concentrating it in another. They are vertically polarized.
 
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#6
In the pictured configuration, these antennas will be somewhat directional horizontally because the mounting mast will reflect some of the RF. The signal will be weaker on the mast side. Some dipole arrays alternate antennas on each side of the mast to even out the pattern and make it more onmidirectional.
 
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#8
Where is that antenna site? The view is looking up the Detroit River towards Belle Isle. Nice pic with the antennas framing the freighters passing in the channel.

btw... those are omnidirectional collinear arrays.
 
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#9
The smaller UHF version is not omni, its a 6dBd gain directional but with a very wide pattern around 120deg. This is due to the elements being around 1/8 to 1/4 wavelength from the mast.

The larger VHF version may be closer to omni but the pattern choices are directional with about 10dB null off the back to cardioid, which is a lop sided omni pattern or bi-directional because the elements are adjustable in distance from the mast. Here is a link to the adjustments for this type antenna: http://www.telewave.com/products/antennas/pdfs/TWDS-7057.pdf
prcguy

Where is that antenna site? The view is looking up the Detroit River towards Belle Isle. Nice pic with the antennas framing the freighters passing in the channel.

btw... those are omnidirectional collinear arrays.
 
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#10
prcguy is correct. These are folded dipole arrays. Not collinear. The VHF antenna certainly looks like a Telewave, it could also be a Sinclair 210-A2. The UHF antenna looks more like a Sinclair. 310-C2 1/4 wave spaced. Element spacing is fixed on the UHF antenna.
 
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#11
This is probably a matter of semantics. The word collinear merely means that the antenna elements are along a common line all in the same plane. In this case, the elements happen to be folded dipoles so maybe a more complete description would be "folded dipole collinear array".

To the OP... looks like only one reply covered it, but polarization is vertical.
 
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#12
I've been dealing with stacked dipole arrays as in individual dipole elements fed with a corporate feedline for maybe 40yrs and I've not heard them referred to as a "folded dipole collinear array" yet. A collinear array is usually meant as a multi element antenna where the elements tie together end to end in some way as in a bunch of half wave verticals with 1/4 phasing stubs between them, etc.
prcguy


This is probably a matter of semantics. The word collinear merely means that the antenna elements are along a common line all in the same plane. In this case, the elements happen to be folded dipoles so maybe a more complete description would be "folded dipole collinear array".

To the OP... looks like only one reply covered it, but polarization is vertical.
 
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#13
I've been dealing with stacked dipole arrays as in individual dipole elements fed with a corporate feedline for maybe 40yrs and I've not heard them referred to as a "folded dipole collinear array" yet. A collinear array is usually meant as a multi element antenna where the elements tie together end to end in some way as in a bunch of half wave verticals with 1/4 phasing stubs between them, etc.

prcguy


I have never heard a folded dipole array referred to as anything else either.
 
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#14
This is just a nomenclature thing. Do a search "dipole collinear array". The terms folded dipole array, stacked dipole array, collinear dipole array all seem to refer to the same thing.

Another type of VHF/UHF antenna refered to as collinear is a number of 1/2 wave sections of coax connected alternately center to shield and covered by a radome.

There are other types of HF/VHF/UHF collinear antennas: stacked, broadside, curtain but they all involve 1/2 wave elements in-line and/or in the same plane.

Just saying... not pretending to be an expert on which terminology is more correct.
 
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#15
Where is that antenna site? The view is looking up the Detroit River towards Belle Isle. Nice pic with the antennas framing the freighters passing in the channel.
Gonna take a shot at answering my own question here. Site looks like it may be on the roof of the RenCen given that there does not appear to be any skyscrapers up river from the site and the roof edge looks to be curved or circular.

Anyway, nice pic, would like to see post from OP as to verification of site location.
 
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#19
Um, er.... the VHF antennae may be two separate folded dipoles - the feeders seem to go off in different directions rather than a phasing harness. One appears to have a swag of ferrite beads on the feeder so may be a transmitter on the end, not much separation if it's a repeater.
 
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#20
Um, er.... the VHF antennae may be two separate folded dipoles - the feeders seem to go off in different directions rather than a phasing harness. One appears to have a swag of ferrite beads on the feeder so may be a transmitter on the end, not much separation if it's a repeater.


It may appear that way, but the individual feeds join in front of the mast they are mounted on. It is 2 folded dipoles connected to one feed line. The length of the individual feed lines are critical length.
 
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