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Patch Antenna Ground Plane - Increase Performance

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I was testing on 900 mhz 500 mw video and was getting very poor results. With a 8 dBI patch from hyperlink mounted on my head with a helmet, the video would become unusable before 2 miles :angry: When I set the helmet antenna down on the ground in disgust, the video suddenly became very clear :o With the helmit sitting on the ground, I got a range of 8 miles... See the attached picture.

I have read about adding ground planes to patch antennas before, but appears that having ground near a 900 mhz patch makes a HUGE difference !!! I would also guess that it helps at 2.4 GHZ.

I am going to add external ground planes to my patch antennas both 900 mhz and 2.4 ghz, does anyone know what size and distance would make the optimum ground plane ? Lots of us use patch antennas and this would be really good information.

Thanks

JettPilot

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Here is an example of an artificial ground plane added by someone to an 8 dBI 2.4 GHZ patch antenna. He said it is 1/2 inch behind the patch mounted with insulated plastic. The ground or reflector seems to be about 12 inches square, as the 8dBI patch is 4.5 inches square.

The guy that made this claims a great signal improvement with this modification. Have any of you guys ever tried this ? I would like to make the same type of thing, but bigger for my 14 dBI patch which is twice the size of the one in the picture below.

JetPilot

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Interesting, not heard of it before.

Seems cheap and easy to do though, could you try it and report back please ?

I would give it a go but I am working on my new 4 way system, hope I dont need to add them to that :unsure:

Terry

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Interesting. Topic "How low can you go?" had mainly concluded that improvements from putting receiver antennae close to the ground were due to shielding from local sources on the horizon.

However, at my local field, which has 'phone and other dishes on a mast in one corner (and the picture gets pretty speckly if I point my antennae that way!) I've definitely got to 400m away with 10mW at an altitude of about 100ft, with no line of sight between my 8dB patches flat on the ground. Not what you'd expect from the radial plot of an 8dB patch.

So, perhaps it's more a ground plane effect, with maybe some really sharp dropoff near the horizon. If it was just sensitivity, why less speckliness?

Has anyone compared a 14dB patch on a tripod pointing at the 'plane with an 8dB patch on the ground pointing straight up? Or, indeed, compared a 14db patch on the ground pointing up with an 8db one... perhaps the 14db is worse, except directly overhead!

Thomas, there must be some way of modelling these effects?

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Thomas, there must be some way of modelling these effects?

I think this is one of those cases where a 'real' test is the only way to go.

I hoped someone would have done a side by side test (one patch on the ground the other on a tripod) by now :(

I would have done it but I don't have two video recorders.

Terry

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I hoped someone would have done a side by side test (one patch on the ground the other on a tripod) by now

You should be able to do a practical test with one Rx. Setup your Tx and a Rx in a large field away from same band RF sources. Get them as far apart as you can. A low power (10mW) would be best to avoid confusion from reflections. Install a DVM on the Rx's RSSI signal. Compare the RSSI voltage with the Rx on the ground and while it is elevated. Look for the highest signal at each elevation. This should give some indication which position is best.

My personal theory as to why the UHF/microwave antenna on the ground works well for some folks is related to the earth acting as a reflective body. A UHF antenna on hard ground puts the radiation angle low enough to reduce nasty reflections. Plus, there is an added bonus of the closely positioned earth slightly squishing down the Rx antenna's radiation angle. Sort of a double whammy. :) But, it could just be due to magic from the microwave gods.

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Wet or constantly damp ground even better for low angle radiation..... Optimum height above ground is about 1 wavelength, but sort of hard to maintain (~2.2") evenly at these frequencies...

Edited by W3FJW-Ron

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You should be able to do a practical test with one Rx. Setup your Tx and a Rx in a large field away from same band RF sources. Get them as far apart as you can. A low power (10mW) would be best to avoid confusion from reflections. Install a DVM on the Rx's RSSI signal. Compare the RSSI voltage with the Rx on the ground and while it is elevated. Look for the highest signal at each elevation. This should give some indication which position is best.

I'm not convinced that RSSI will tell the whole story, my guess is that it may be as much to do with cutting multipath and reducing interference from other band users, thats why I would like to see a side by side test in the air. Nice testing days seem few and far between here at the moment, last weekend was good but I had to work :(

Terry

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FWIW, the RSSI method is helpful because it may provide useful clues:

(1) If the RSSI voltage changes with antenna elevation, then that indicates that the performance change is due to signal strength. (2) If the RSSI provides contrary information, or does not change, and the video signal gets worse, then the performance difference is caused by the reception of competing RF signals.

Plus, using the same Rx and antenna for all the tests eliminates equipment performance issues. This is big advantage, since I have noticed RF performance differences between "identical" systems.

For sure, this data would need to also be validated with a comparison test using two systems. No argument from me about that. But, like you, I''m too busy to do the testing. Plus, I'm not really that curious about it. So, someone else gets to experiment. :)

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well I was going to play with my newly purchased left and right circular patch antennas with Oracle, but perhaps I will test the 8db and 14db patch first. I used to fly with my 14 db on a tripod and had not so good results because of too narrow of a beam along with static. Now I use my 8db patch on the ground and have almost static free flights, mind you the 14db did give me some awesome range. (2KM) But needed a spotter to constantly point the patch at the plane.

8db patch on the ground

8db on a tripod (notice more static on this video)

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And did the spotter saw your plane at 2km?

For me with Oracle there is no need to fly with a spotter any more, and 2km with Airwave 500mW is easy achieved with my 2 8dbi home made patchs (GPP, CPP) Would like to try a double biquad (14dbi aprox), and I think I wouldn´t need a spotter too with Oracle.

The other day I reached 5km with those patches, th image had some noise but I think the patches were a bit off the plane´s line. How far you guys have you reached with either GPP or CPP? What would be the theorical distance with the 500mW tx and a standard rx?

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JMS thats the closest I have seen to a side by side test but I think I need to see it side by side to convince myself the difference is not for any other reason.

It would be much easier if there were another FPVer near me and we could share resorses to run the test, do any of you guys live close to each other ?

Terry

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My 2Km trip was done last year but since then our gear has improved a lot since (God bless Mr.RC-CAM ;) ) BTW the spotter (me) did see the 2KM trip... we actually lost the plane but managed to fly back by static video.

Now that I have a few OSDs kicking around and patiently waiting for I.F. RF link, I love to push the limits of my 500mW Airwaves, Lawmates, Gospellar and another brand that I.F. was toying with (as soon as I get my hands on it and they claimed best results over all the brands). And yes I too will use my Oracle and record/post this flight.

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I'll be down in Bradworthy, N.Devon, 16-23 August - nice long way from major roads and 'phone masts. I'll take a 2nd recorder, and as it's a holiday, I should even have the time to get some simultaneous footage.

Come to think of it, Terry, that's not a billion miles from Taunton! PM a 'phone number, we might be able to converge at some point.

However, I think Mr RC-Cam's point about comparing like with like is important; I guess one could swap Rx aerial positions mid-flight... or I should dig out my old receiver that has an RSSI meter.

I guess the gold standard would be to log servo positions, GPS data and RSSI simultaneously. You could then build a real-world real-time 3D radial plot which factors in the orientation of the Tx aerial too. A project for the autumn*, perhaps.

(*Autumn 2020...)

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Bradworthy, hmmm, if your getting there on the M5 you will drive past me at j24. Give me a call if you want to meet up, I met chargenut from rc groups a couple of months back and even got to have a fly of his quad copter, great fun.

A split screen video of both patches would be the best, must look out for one of those old cctv units.

Terry

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OK, being a fan of backyard laboratory work, here are some initial test figures with an 8dB patch antenna attached to my trusty 'tobacco tin' receiver, which has a meter on the RSSI output, with 100% = max signal, 0% = no signal. 10mW Tx (TX40) about 1m off the ground:

Zero feet - 90% signal at all angles/heights. (ah-hem, yes, this really should be 100%;I'll calibrate it again any day now, but it held pretty stable on any reading, and this won't affect the sign of any results...)

8m away:

- patch straight up: 55% signal on the ground, rising to a max of 65% at about 1m.

- patch pointing at Tx: 55% signal on the ground, rising to a max of 65% at about 1m.

I suspect such results should be viewed while listening to "Deliverance"-style banjo music i.e. loads of multipath, probably meaningless. Even I won't believe any such data until pointing the patch, held off the ground, at the transmitter shows an increased signal <_<

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Thanks for the test results.

Now repeat that simple test while out in a wide open space with much further distance between the goodies Perhaps a couple hundred yards. BTW, don't let your human helper hold the Rx/Antenna (use a tripod and stand at least a couple meters behind it all).

If the RSSI continues to show that the signal is weaker when the Rx is directly on Earth, then that eliminates at least one of the theories. So, all the little observations tell a story.

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Just curious here from a hams point of view. Has anyone ever tried just a random length of long wire, say 10 or 20 feet in a horizontal and vertical configuration on the receivers antenna input..?

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Step 2- flat field, 10mW TX40 as before about 1m off the ground.

8dB patch about 50m away:

- on the ground, signal 10%. No particular increase in signal moving aerial flat to 90 degrees.

- 1m off the ground, signal 50%. Rising to 55% as it tips to 45 degrees, then back down to 50% at 90 degrees (i.e. pointing at the transmitter).

So, "earth ground plane blocks out interference" theory 1, "earth ground plane boosts sensitivity" theory 0.

Unfortunately, the next step really does need a transmitter more than a metre off the ground, and fiddling around with receiver aerial height while a 'plane is flying around is going to get trickier.

Again, the health warning - I noted variations of 10% or more, as I stood 1-2m away (i.e. close enough to see the RSSI reading), just me swaying back & forth a few cm - presumably multipath off me (the only vertical object on the field). I suppose I could use a spotting 'scope to view the meter from a distance... I'd feel like someone testing a bomb B) I still won't feel happy until the signal is at max when the patch is pointing at it...

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I suppose I could use a spotting 'scope to view the meter from a distance.

I know what you mean. I use low power binoculars so that I can get away from the RF test zone. I have a pair that cost $1 at the discount store that works fine.:)

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I just received my diversity gear(thanks Vova), and would like to do some field testing regarding this antenna placement question. I have a 5' helium balloon to use as a Tx platform, so it will be possible to park the Tx at altitude and play with different Rx placements without worrying about flying a plane at the same time. I've got a 5dBi whip, a 8dBi patch, plus the original whips that come standard, all on 900mhz running through an oracle. If there is anything that Folks want me to try let me know.

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If you'll be using a diversity system during the tests, then I recommend that you set it up for manual switching. Otherwise, the diversity switching may mask the issues that you are trying to evaluate. For sure, being able to easily switch between the two Rx antennas will allow you to conveniently evaluate how the aerial height above ground affects their individual performance.

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If you'll be using a diversity system during the tests, then I recommend that you set it up for manual switching. Otherwise, the diversity switching may mask the issues that you are trying to evaluate. For sure, being able to easily switch between the two Rx antennas will allow you to conveniently evaluate how the aerial height above ground affects their individual performance.

I thought that I could use the oracle to tell me which antenna had the best reception, as I do not have any testing gear. I figured that I would try different positions with identical antenna and see which one the oracle chose.

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