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pseddon

Setting up Diversity Antenna

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I have two goof patches and an Oracle diversity receiver. I have read I need to have the antenna 1.5, 2.5, or 3.5 etc wavelengths apart. What is the best way to optimise the setup:

1. At what angle to the horizon should they be set?

2. At what angle relative to each other should the patches be set (ie in the horizontal plane)?

3. Are the patches polarised and do they have to be set up in a particular orientation?

Any help would be appreciated.

regards Peter

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It all depends on your flying. Long range? overhead? aerobatic? built up area? mixture of any of these?

Terry

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I agree with Terry, it all depends on the "antenna issue" you intend to solve. Environment, flying style, flight path, etc., all affect the choice of diversity antennas and their placement. There are some very strong opinions out there on what is best. But, I can say that "best" depends on the many factors.

Here's some examples (when all you have are two GP Patches and a diversity system like Oracle):

Spatial Diversity: Minimum required distance is at least a half wavelength, "best" distance depends on the RF expert you ask. Both antenna designs must match, have the same polarization orientation, and direction/orientation must be the same. Used to combat multipathing / Raleigh fading.

Polarization Diversity: Both antennas pointed in same direction, but with 90 degree difference in polarization orientation. Typically no minimum required distance. This is used to help improve cross polarization issues, such as when a stunt model airplane steeply banks. No expected improvement to multipathing problems.

Beamwidth Expansion: Both antennas with same polarization orientation, pointed in non-overlapped directions. This is used to effectively add the two antenna radiation patterns together to increase their practical beam widths. No improvement to multipathing problems.

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Oracle was designed to be a spatial diversity system (but not be limited to that use). So it has the extra hardware and software to help reduce multipathing/Raleigh fade events. However, now that long distance flight is the big thing, it is not always used as common diversity antenna device. Instead, I see it being used as an automatic antenna switch to select between a high gain directional antenna (GP Patch is common) and some other antenna, such as a omni whip. This is yet another use for a diversity controller, but is certainly not a true diversity solution.

Plus, there are users that have created hybrids of the different methods discussed above, such as using two patches that are loosely pointed in the same direction (typically with 50% beam overlap). This can offer some multipathing reduction and increase the effective beam width.

All antenna choices and diversity solutions are compromises. Nothing is "best" for every installation or every flying location. Having several rx antennas in the flight box, and a willingness to experiment with them often, is perhaps the best solution.

Responses to your questions:

1. At what angle to the horizon should they be set?

Think in terms of a geometry math problem. The angle depends on distance and height of the model aircraft. There is sufficient beam width in the GP Patch that a reasonable compromise would probably be about 45 degrees. But every situation is different, so experiment with the angle.

2. At what angle relative to each other should the patches be set (ie in the horizontal plane)?

Depends on what you are trying to achieve. See above.

3. Are the patches polarised and do they have to be set up in a particular orientation?

Yes, they are linear polarized. I believe the polarization orientation is shown on the plans. The polarization must match the transmitter's antenna: vertical is the expected choice for our application.

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Thanks for the very useful help. With the information you have given I think the next step is test and retest.

To answer the fundamental question - flying style is gentle not 3D and always in front of the pilot up to an elevation of about 80degrees and azimuth of +/- 90degrees, short range - visual.

One last question - I have read that the antenna are best mounted close to the ground rather than on a tripod - any thoughts?

regards Peter

I agree with Terry, it all depends on the "antenna issue" you intend to solve. Environment, flying style, flight path, etc., all affect the choice of diversity antennas and their placement. There are some very strong opinions out there on what is best. But, I can say that "best" depends on the many factors.

snipped to save space....

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I have read that the antenna are best mounted close to the ground rather than on a tripod

If you are suffering from multipath related ground reflections then putting the antenna close to the ground may help reduce them. Putting the antenna up high may help with very long range flight. So, once again, "best" depends on what is best for the particular situation.

For example, for your short range visual flights I would lean towards putting the GP Patch close to the ground. But it would be wise to also try it on a tripod too to see if it works better.

I propose that there is no single "best" for every FPV situation. And to make things more interesting, what is best for a particular time of year, might not be best at another time. So, if you are looking for best, be flexible in your installation and be willing to experiment.

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I feel much better after that reply!!!

Cut and Try seems to be the answer.

Thanks for the help, Peter

If you are suffering from multipath related ground reflections then putting the antenna close to the ground may help reduce them. Putting the antenna up high may help with very long range flight. So, once again, "best" depends on what is best for the particular situation.

For example, for your short range visual flights I would lean towards putting the GP Patch close to the ground. But it would be wise to also try it on a tripod too to see if it works better.

I propose that there is no single "best" for every FPV situation. And to make things more interesting, what is best for a particular time of year, might not be best at another time. So, if you are looking for best, be flexible in your installation and be willing to experiment.

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