Double dipole antenna ... novice question

[scan_nepal]

Hello all,

While searching Internet, came across this photo:
http://hometown.aol.com/teraycoda/images/dipoleontower.jpg

I have seen such antennas in many places as well. I would like to know how the connection is made between those two dipoles. Is such antenna better than, let's say, yagi?

Thanks in advance.

(P.S. Sorry if I asked a novice question)

 

[blueangel-eric]

Hello all,

While searching Internet, came across this photo:
http://hometown.aol.com/teraycoda/images/dipoleontower.jpg

I have seen such antennas in many places as well. I would like to know how the connection is made between those two dipoles. Is such antenna better than, let's say, yagi?

Thanks in advance.

(P.S. Sorry if I asked a novice question)

they can be to an extent. they're called a dipole array. most the time i see them as a set of four. they are phased together with a phasing harness, which is a coax that is spliced together to connect to each one. they can be omni directional or you can arrange them on the mast to be more bi-directional.

Eric Burris kc0ldt

 

[kb2vxa]

OK, here's a mouthful for you, it's a two bay phased folded dipole array. Each bay is spaced a half wave apart and operated in phase with a coaxial power divider AKA phasing harness. For added enjoyment add two more bays and another power divider, or keep adding dual bays until you reach the stratosphere which isn't too hard, they're bigger and wider spaced than they look from the ground especially in a photo. That array is approximately 20' end to end, maybe just a tad more, I haven't done the math.

"they can be omni directional or you can arrange them on the mast to be more bi-directional."

Er, no. That array is omni directional, a four bay would have each spaced 90 degrees from the next circling the mast. If they're all on the same side a cardioid or D shaped pattern results. You can get a SOMEWHAT bidirectional pattern but only with four bays, two on each side and like I said that two bay array is omni.

Here's a short (?) story for the techies out there. A few years ago some NYFD hams (yeah, firemen) put together one of the best linked repeater systems I've ever seen with a four dipole array on the 220MHz repeater. It had great coverage until they took it down temporarily for some reason and when they put it back up it had such a skewed radiation pattern I nearly lost the signal entirely here at the Jersey Shore. They went nuts trying to figure it out, they put it back together right, NOT. They insisted the power divider was right so why the cockeyed phasing? Well take it down again, I'll bet you did SOMETHING wrong in mounting the dipoles. Sure enough two were upside down which reversed the phase with relation to the other two throwing the pattern all out of whack. The trustee/license holder made the comment "Why didn't >I< think of that?" and I just laughed, that was insult enough. (;->)

Eric Burris is Casey Oldt? So why not Casey Jones? Nice shot of the BNSF War Bonnet though. (;->) Just to hijack the thread temporarily, do you recognize this locomotive?

 

[DPD1]

I've never been crazy about them, simply because you're adding so much other stuff in the line to make it work, for little advantage. The more stuff in there, the more there is to go bad eventually. I've seen them used in transportation applications where you have a 90 degree angle in the road or rail line, and you can create a little bit of directional action using that. But you could accomplish the same thing in less complicated ways. A collinear accomplishes the same thing, without all the extra stuff out in the weather getting ready to break.

Dave
www.DPDProductions.com
Antennas & Accessories for the RF Professional & Radio Hobbyist

 

[blueangel-eric]

OK, here's a mouthful for you, it's a two bay phased folded dipole array. Each bay is spaced a half wave apart and operated in phase with a coaxial power divider AKA phasing harness. For added enjoyment add two more bays and another power divider, or keep adding dual bays until you reach the stratosphere which isn't too hard, they're bigger and wider spaced than they look from the ground especially in a photo. That array is approximately 20' end to end, maybe just a tad more, I haven't done the math.

"they can be omni directional or you can arrange them on the mast to be more bi-directional."

Er, no. That array is omni directional, a four bay would have each spaced 90 degrees from the next circling the mast. If they're all on the same side a cardioid or D shaped pattern results. You can get a SOMEWHAT bidirectional pattern but only with four bays, two on each side and like I said that two bay array is omni.

Here's a short (?) story for the techies out there. A few years ago some NYFD hams (yeah, firemen) put together one of the best linked repeater systems I've ever seen with a four dipole array on the 220MHz repeater. It had great coverage until they took it down temporarily for some reason and when they put it back up it had such a skewed radiation pattern I nearly lost the signal entirely here at the Jersey Shore. They went nuts trying to figure it out, they put it back together right, NOT. They insisted the power divider was right so why the cockeyed phasing? Well take it down again, I'll bet you did SOMETHING wrong in mounting the dipoles. Sure enough two were upside down which reversed the phase with relation to the other two throwing the pattern all out of whack. The trustee/license holder made the comment "Why didn't >I< think of that?" and I just laughed, that was insult enough. (;->)

Eric Burris is Casey Oldt? So why not Casey Jones? Nice shot of the BNSF War Bonnet though. (;->) Just to hijack the thread temporarily, do you recognize this locomotive?

from what i see from DB products is that when the dipoles are lined up on the same side of mast it makes the radiation pattern more elliptical. So it's more directional. maybe i got confused with bi directional.

I don't recognize that locomotive. I keep up with the modern stuff more.

Eric Burris
kc0ldt

 

[kb2vxa]

Hi again,

What Dave is trying to say is a multi dipole collinear array can be made directional for that "right angle bend in the road" but the "collinear" he's talking about cannot. That's a common term for an end fed multi wavelength antenna usually encased in PVC or fiberglass. The confusing part is "collinear" so here's the definition;

collinear (k„`l€n€) adj.
1. lying on the same straight line.
2. having a common line.

Well Eric you're in the ballpark. It's not in my dictionary so here's the best definition I can give you. Cardioid (heart shaped) is a geometrical shape like a D with the bar pinched inward, "elliptical" is close but no cigar.

Darn, I thought my mention of Casey Jones would give you a clue. That's the Cannonball 2 at the Casey Jones Museum in Jackson TN identical to the one he wrecked .

 

[blueangel-eric]

Hi again,

What Dave is trying to say is a multi dipole collinear array can be made directional for that "right angle bend in the road" but the "collinear" he's talking about cannot. That's a common term for an end fed multi wavelength antenna usually encased in PVC or fiberglass. The confusing part is "collinear" so here's the definition;

collinear (k„`l€n€) adj.
1. lying on the same straight line.
2. having a common line.

Well Eric you're in the ballpark. It's not in my dictionary so here's the best definition I can give you. Cardioid (heart shaped) is a geometrical shape like a D with the bar pinched inward, "elliptical" is close but no cigar.

Darn, I thought my mention of Casey Jones would give you a clue. That's the Cannonball 2 at the Casey Jones Museum in Jackson TN identical to the one he wrecked .

According to DB Products in the PDF about those dipoles they use the term elliptical and its more round than heart shaped.

Eric

 

[N1BHH]

When Rockland, MA. Fire went UHF, at first they had an 8-pole array with the pattern set north and south since the town is situated north and south. There were a few problem areas, so they switched to a Stationmaster and that made things better, no holes in coverage. With the 8-pole it had some huge nulls to the west and east, so when they went on a mutual aid response in those directions, signals went unreadable.

The advantages of a multi dipole array are pretty much like putting a signal into a particular direction where you need it. Broadcasters especially sometimes have directional arrays, they have to protect a station a few states away and have to skew their pattern at night, in particular, to protect the other station's listening area.

 

[N_Jay]

According to DB Products in the PDF about those dipoles they use the term elliptical and its more round than heart shaped.

Eric

Well they are wrong because Warren never is!:evil: :lol: :evil:

 

[kb2vxa]

"According to DB Products in the PDF about those dipoles they use the term elliptical and its more round than heart shaped."

In geometry there is considerable difference between ellipse, circle and cardioid so N_Jay for once is correct, they are wrong and Warren never is.