What would happen...

[KD3Y]

Hello fellas,

I currently use a 40 m dipole, oriented NW to SE, up about 26 feet in the trees.  I get good coverage north and south but poorer coverage east and west.  I've been told sometimes dipoles radiate more broadside and less off the ends.

What would happen if I build a "dual dipole" sort of like a fan dipole, both antenna 40 meters, but one perpendicular to the other, and one about 8 inches higher than the other, with one antenna oriented east-west and the other antenna oriented north-south?  Sort of like a + layout, both antenna fed by the same feedpoint.  Do any of the antenna guys here have any ideas if it would get good results or bad results?

Surely it's been tried before.   Just thought I would ask before trying to re-invent the wheel.

I did find this via google:   "Circular polarization can sometimes improve the match over a crossed polarization. One way to do a circular polarization is to have dipoles at 90 degrees...but they have to also be phased correctly. Either not coplanar or with a phasing harness between them."

But all that phasing, coplanar, etc lingo is beyond my antenna comprehension.  LOL
Can anyone translate?

Thanks,
Anthony, KD3Y

Edited April 7, 2023 by KD3Y

[K3MRI]

I'll give you a long answer, from experience, because I have done this extensively. However, first a question... We agree that you are trying to run the two together, correct? This is not about having two switched dipoles?

[KD3Y]

Right.  Two antennas run from one feedpoint, not two dipoles that can be switched from one to the other.  Both radiating at the same time when the radio Xmits, one radiating E to W and the other N to S simultaneously as if one single antenna.

[K3MRI]

Here is a link to the definitive scientific article on 'crossed dipoles'.

https://www.researchgate.net/publication/282776048_Crossed_Dipole_Antennas_A_review

It's not an 'easy read' but it will tell you everything you need to know.

Note that there are different ways of wiring up the dipole, you'll see that in the article. I've tried the three major ways, crossed, crossed trident and crossed asymmetric. You can also create a crossed multi-band.

Let me know when you've read the article, and maybe a couple of other online references to 'crossed dipoles' and then I can go deeper into what I found works best and what doesn't. Remember to look at both 'same band' and 'different band' versions.

[WA3LTJ]

Great article. 

Here is a link to a book (in PDF format) on a topic that has always fascinated me, planar antennas.

http://www.edatop.com/antenna/img/tianxian-563szwchfqytdd.pdf

 

 

[K3MRI]

On 4/12/2023 at 3:02 PM, WA3LTJ said:

Great article. 

Here is a link to a book (in PDF format) on a topic that has always fascinated me, planar antennas.

http://www.edatop.com/antenna/img/tianxian-563szwchfqytdd.pdf

 

 

Now that, my friend, is what I call a definitive piece of work. Wow. I'll download it, flip all the pages 90-degrees, and find time to read more of it than is wise. You know, if I were to start my career over, and I am being serious, I would consider becoming a transmission/broadcast engineer! Long Live The Wave!

[KD3Y]

Thanks Jim and Andy.  That answers a lot of questions.

"Turnstyle" antenna.  Well that name makes sense.  So that's what a "phasing line" is.
So does my 1/4 wave phasing line need to be 1/4 wave long (about 34.5 feet) or is that just the name and not the application?

 

 

 

I suppose this is a separate topic, but how does a phasing line work?  Why not just solder two legs of the dipole to the coax shield and the other two legs to the coax center?  What does the loop of phasing line do?

Anthony, KD3Y

[WA3LTJ]

This type of antenna can be used for different purposes. With the 1/4 wave phasing it becomes circularly polarized, which is good for certain circumstances, like satellite work. 

[WA2WMR]

On 4/6/2023 at 9:03 PM, KD3Y said:

Hello fellas,

... I've been told sometimes dipoles radiate more broadside and less off the ends...
Thanks,
Anthony, KD3Y

If I remember correctly, dipoles normally radiate more broadside. That is for half wave dipoles, If you go for 1.5 wave dipoles, the main lobe splits and starts swinging around toward the ends. So if you have a 40m dipole and run it on 15, I believe this would happen. But a half wave dipole radiates broadside. Now if you have a lot of stuff around it like trees, buildings, etc, it may behave differently.