CA on omnidirectional antennas?

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mattvds
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CA on omnidirectional antennas?

Post by mattvds » Wed May 02, 2018 12:38 am

I have a lot of trees and hills around my house, and was unable to get reliable B41 reception on the high gain directional antenna I purchased (only was able to get a ping lock once, and no CA, so speeds were pretty slow).

However, I am able to get decent speeds using some cheapo antennas that came with my PCIe/USB/Sim card combo on B26 (16mb down/10mb up). Therefore, I'm wondering if I would be able to get B41 with a good outdoor omnidirectional antenna. Is it possible to get CA with omnidirectional antennas? How would you position them so they are 90 degrees out of phase?

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JimHelms
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Re: CA on omnidirectional antennas?

Post by JimHelms » Wed May 02, 2018 8:17 am

mattvds wrote:
Wed May 02, 2018 12:38 am
I have a lot of trees and hills around my house, and was unable to get reliable B41 reception on the high gain directional antenna I purchased (only was able to get a ping lock once, and no CA, so speeds were pretty slow).
As a general rule, directional antennas perform best with Line-of-Sight (LOS) with the tower--with little to no obstructions. Signals from the tower can bounce and scatter off objects in different directions, so it is possible to "receive" these signals, or random pieces thereof, and possibly from more than one cellular tower. But, more often than not, they are unusable. Directional antennas generally have a fairly narrow focal point, and the antenna transmits/receives in that direction. It is akin to how a satellite dish functions.

However, I am able to get decent speeds using some cheapo antennas that came with my PCIe/USB/Sim card combo on B26 (16mb down/10mb up).
The reason your "cheapo" antennas can out perform your directional is because they are omni-directional. By their very nature, they are able to receive and transmit signals on a 360 degree radius. They are more forgiving of obstacles and better suited for signals that are being scattered.

This is demonstrated in the rather crude illustration below.


Omni vs Directional.png
Omni vs Directional.png (18.12 KiB) Viewed 1113 times

Therefore, I'm wondering if I would be able to get B41 with a good outdoor omnidirectional antenna. Is it possible to get CA with omnidirectional antennas?
This is a difficult question to answer. It first would depend on whether the tower has band 41. While the vast majority of Sprint towers/antennas include the 2500HMz (Band 41) frequency, there are still a few that do not. Since Sprint uses band 41 for Carrier aggregation (though now rumored to include band 25), without Band 41, there is no CA. CA is obtainable on omni-directional antennas. A single omni-directional antenna is capable of receiving CA (although not MIMO).
How would you position them so they are 90 degrees out of phase?
Good question, and one not easily answered. Lets first consider placement when using two omni-directional antennas. There is a valid argument that, for optimal placement, the antennas should be configured where both are perpendicular to the tower. This logic can be demonstrated in the image below with Tower 2:

Dual Omni Antennas.png
Dual Omni Antennas.png (17.87 KiB) Viewed 1113 times

Now consider your question on how to phase the antennas at 90 degrees (+45/-45 degrees from one another). The image below helps to visualize this cross polarization of two separate data streams used for MIMO:


Cross Polarization.png
Cross Polarization.png (24 KiB) Viewed 1113 times


The full 90 degree relationship can be shows as:


+45 -45 Waves.gif
+45 -45 Waves.gif (847.63 KiB) Viewed 1113 times

I have tested the Omni-directional antennas in the two configurations below. I am certainly no expert in antenna technology but my intuition was that the antennas should work best at the +45/-45 position. But, to be honest, there were little to no difference in their performance when tested. Of course, my tests were conducted on open terrain with no obstacles between me and the tower.

Configuration Test.png
Configuration Test.png (3.51 KiB) Viewed 1113 times

What I have come to learn (and accept) is that there is no one-shoe-fits-all solution when it comes to antenna placement and configuration. There are a lot of variables that come into play.

Those willing to use a little logic coupled with some trial and error to test configurations, will certainly benefit the most.

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Re: CA on omnidirectional antennas?

Post by mattvds » Sun May 13, 2018 9:36 pm

CA worked with two omni antennas without issue. Signal strength is a bit weak (64%), but am able to lock onto B41 and get CA. Speeds now ~45 down, 4 up. Download is obviously way better, but up is much lower than B26. I assume this is due to weaker signal strength. I'm happy with this as I don't really upload much, and now I don't have to worry about 2 people streaming netflix at the same time.
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JimHelms (Sun May 13, 2018 10:03 pm)

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