Antenna Walkabout at 5.8GHz

[Hands0n]

The neighbours must think the bloke at number 232 is completely bonkers tonight.  For there I was, conducting a walkabout antenna test between a FatShark rubber duck, Gav';s Skew Planar and my own Helical that I constructed recently (piccy below) using my 3D printer, some twin and earth copper wire and a pigtail kindly sourced from @teslahed (thank you kind sir).

On the dining room table was my Alien 450 quad with GoPro Hero3 Black attached to a FatShark 200mw VTX with one of Gav';s Skew Planar antenna for the transmitter side. 

For the walkabout I used my FatShark Attitude goggles.

My walkabout was out of the back of the house, through to the end of the garden, out into the street and as far as I could walk away up the street before apparent signal break up or loss.  So, with the quad on the dining room table, the signal would have to pass through the outer walls of the house, there are windows, through the conservatory and its glass windows before hitting clear air. At the end of the garden the signal would have to pass by two parked cars, a concrete garage with steel roof, various trees and bushes before hitting clear air in the street itself.  It has been raining today so the leaves and ground are wet, the air is damp.

1. The FatShark Rubber Duck (35 meters)
I have to assume that FatShark quality prevails and that the rubber duck antenna is tuned to 5.8GHz frequencies. And so the walkabout did not last very long. I made it just up to the end of the garden and out of the rear gate into the street when the signal started to break up significantly. I had walked no more than 35 meters.

2. Gav';s Skew Planar (85 meters)
I then mounted the RX Skew Planar antenna to the FatShark goggles and repeated the test. This time I got much further along the road before the signal started to break up. I made it to 80 meters at which point a lot of snow was showing on screen.  I crossed the road to provide a clearer line of sight with the house, but things didn';t improve much if at all. By 85 meters the signal fell away.

3. Helical Antenna (140 meters+)
Next up I mounted the Helical and hand held it to stop it flopping all over the place. I walked the exact same path, this time reaching the end of my road at 140 meters where the signal was having to pass through many front gardens surrounded by high hedges or wood fences. Also the line of sight with my house was completely obscured by the houses themselves, all 1930';s build. The signal, when the Helical was pointed towards my house was clear of any noise.  Rotating on the spot the directionality of the Helical was very obvious where facing away the signal was noisy to the point of loss. Turning to 90 degrees of home the signal returned, noisy but very viewable, even the OSD characters were clear enough to read. Turning to face the general direction of the home resulted in a rock solid signal, no noise, no interference whatsoever. The Helical was pulling in the signal as if I were standing next to the VTX in the dining room.

So I crossed the road, again to improve line of sight, the signal still having to penetrate bushes, trees, hedges. The signal was as good as above. But now the side-on reception was improved again.  And certainly the beam width was pretty much around the 52 degrees that the antenna calculator indicated.

I never got to find out how far the Helical would work before the signal dropped off as I ran out of road. It was cold, dark, and I really did not fancy walking out even further still. That is an exercise for another day.

Conclusion:
The conditions were harsh for radio at 5.8GHz, completely sub-optimal. They were also completely unrealistic for FPV flying as the aircraft was indoors and on the ground. Whereas in FPV use the aircraft would be airborne with altitude that would generally allow the signal to propagate further than this test.

The Helical antenna has it, hands down. Gav';s Skew Planar was a close second, but they are omnidirectional and while improve transmission/reception they do not match the comparatively highly directional Helical.  The rubber duck are hardly worth discussion.

Going forward, I will continue to routinely use the Skew Planar antenna as they are more compact and work really well. But for awkward conditions, or further distance FPV flights I will be swapping over to the Helical on the RX end of the video link.

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[nub]

nice write up.

is there a way to work out the 52 degrees beam width into meters at a particular distance?

say at 100m, 200m, etc etc

just something i';ve always wondered about

[Biffa]

Good informative post Danny

They work remarkably well for very little outlay, and knowing you made them yourself and they actually work is a great feeling

[Hands0n]

nice write up.

is there a way to work out the 52 degrees beam width into meters at a particular distance?

say at 100m, 200m, etc etc

just something i';ve always wondered about

There is going to be some mathematics for working out the breadth of the cone at a given distance but it is beyond my schoolboy understanding of such things ::)  But thinking about it, the further away the aircraft the broader the area that is covered by the cone of signal reception.   52 degrees is quite a wide angle, the area of coverage expands quite broadly, quickly.

If you find a link to the math please share ... I';d like to know also now ::)

[Amorgos]

Great post HandsOn. Very useful. I was actually gearing myself up to do a very similar test probably at the end of the week. I want to test...

• 600mW ImmersionRC
• 25mW ImmersionRC
• Standard ImmersionRC Whip antennas
• ImmersionRC / Fat Shark CP antennas
• Gav';s antennas which I got through the post today. (Cheers Gav!)

I';ll be using a 30dB attenuator on the transmitter which will basically cut the range by a huge amount so I will be able to test all antennas line of sight, without having to use my legs too much. I';ll post the results!

[Hands0n]

Awesome Amorgos, that';ll be interesting to see what you get for a given antenna/VTX combination.  Gav';s antennas are superb, been working ever so well. 

I';m thinking of taking the Helical out for a little drive in the car, see how far away I can get along the main road which is fairly straight.

Looking forward to seeing your tests/results

[n506]

I';ll be very interested to see the difference between Gav';s antennas and the ImmersionRC CP ones. I';ve noticed quite a difference in picture quality with Gav';s antennas, and it certainly seems more locked in for a further distance, but haven';t done anything scientific to judge just how much!

[nub]

There is going to be some mathematics for working out the breadth of the cone at a given distance but it is beyond my schoolboy understanding of such things ::)  But thinking about it, the further away the aircraft the broader the area that is covered by the cone of signal reception.   52 degrees is quite a wide angle, the area of coverage expands quite broadly, quickly.

If you find a link to the math please share ... I';d like to know also now ::)

found an easy way to work it out i think

http://www.calculator.net/triangle-calculator.html

[jimbo385]

Nice one guys!

I';s always good to get a comparison side by side all tested with the same equipment. It would be interesting to add to the table price which adds another dimension .

@Handson. Danny would be useful to pass on your antennae to Amorgos for him to test with the same parameters.

[fruitsalad]

you should of done some john cleese funny walks to go with it danny,thatve the neighbours talking 
good test info 

[Hands0n]

@jimbo385 - in terms of cost it is all rather modest.

FatShark Rubber Ducks - £0 (included with the Attitude goggles)
Gav';s Skew Planar - £30 a pair
Helical - £3 (estimated as uses very little ABS filament, twin&earth scrap wire, SMA connector (£2), pigtail wire (£1 est.).

[Amorgos]

@Handson. Danny would be useful to pass on your antennae to Amorgos for him to test with the same parameters.

PM me and I';ll reply with my address. Always nice to get some stuff to play about with through the post I';ll post them back of course!

[Hands0n]

PM me and I';ll reply with my address. Always nice to get some stuff to play about with through the post I';ll post them back of course!

PM sent ::)

[richardg6paj]

This quite interesting.
http://www.changpuak.ch/electronics/calc_12a.php

Richard

[Hands0n]

A nice find Richard.

I ran the simpler Helix Antenna Calc http://www.changpuak.ch/electronics/calc_12b.php  which closer matches the design I built to.  Interesting that it is suggesting an 11dBi gain - but I guess it is all in the same ballpark as the 9dBi gain from the other calculator I used.  Both are creditworthy gains, nice to be had ::)

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[richardg6paj]

Hi Danny
I was wondering how the reflector would be constructed. Looks as though it might have to fabricated in copper.
Not as easy as what you';ve done.

Richard

[Hands0n]

Hi Richard,
The reflector/groundplane can be anything you like that is metallic. I used copper-clad PCB cut to shape and drilled for the coax to pass through. It could equally have been solid copper or even aluminium.  In theory you could even use a bit of kitchen foil glued to a piece of cardboard (you may have seen those self-build parabolic WiFi reflectors?). 

The all important gubbins is the helical coil itself, its dimensions in terms of coil diameter and spacing to attune it to the radio frequency required.  From what I read, the Helical design is very wideband and so minor errors in such dimensions will not be terribly significantly impacting on dBi gain efficiency.

I also read, and am advised, that at 5.8GHz there is no need for some of the additional complexity of constructing RF matching for the Helix.  Which is nice ::)

[richardg6paj]

Hi Danny, yes I get what your saying. I didn';t make myself clear on my previous post. (a failing of mine).
I meant the construction of the reflector on the example shown on the calculator.

I';m going to have a go at making a former and reflector out of g10 and like you say copper clad board for the reflector.
I read somewhere that the wave trap wasn';t needed if you use 10 swg (1/8") any less you might need one. 
I guess it';s all experimental, which makes it fun. Is your panel mount sma , male or female.
I don';t have any FPV gear at the moment so reading as much as I can before taking the plunge.
I must say I have learnt a lot from this forum, a great bunch of people.

Richard

[Hands0n]

Ah, ok, I see    So the reflector shown on the calculator, using your original link to the calc, is more complex than the one I built.   It seems to me that the wavetrap is part and parcel of the helix, at the base where the wire is formed straight and just before it joins the PCB or panel mount SMA connector.

In my build I used a pigtail cable to the reflector and helix.  I have some PCB mount SMA coming but think they';ll complicate the build for me.  The SMA connector I used is female and has the pin (they confuse me as they use the shell to define gender).

I do not have the kit to measure the actual gain of this build - but the effectiveness of it suggests that it is doing its job rather well. 

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[Hands0n]

A late addition.

Attached to this post is a ZIP of the two STL files for 3D printing