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Old May 31, 2012, 05:02 PM
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Quote:
Originally Posted by nogas View Post
You may find post 3 is talking about building for 1280mhz. Different kettle of fish.

Hey Markus, can you confirm if my measurements are correct?
Not sure what you mean with "Coil centres" but I asume you refer to "Winding step (between centers)" or "s" as it's shown on jc opens page. If so, it should be 11.8mm for your case.

Based on my experiance, there is no way to "pre calculate" the other parameters to the degree you would like. As mentioned many times in discussions around 5.8Ghz CP antennas, tolerances and factors having influence are such that you can't do that. You have to build something, measure, then apply corrections. If you can't measure, build such that you can be sure to at least end with a useable result. Alas go wideband.

The definately most critical areas of a helical - provided you stick to the calculated parameters - are the feedpoint and the wavetrap. Precalculating them so as you end up with an antenna being highly resonant where you want it and then just build it to measure - impossible. So unless you have access to a vector network analyzer for the tuning process I recommend you to use a thicker wire ( 2mm for your frequency ) and mount the precalculated wave trap to the center of the first turns quarter.

HTH

Markus
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Old May 31, 2012, 08:28 PM
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Highland, CA, USA
Joined Jan 2001
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For a 5.8 antenna are there any thoughts on using 1mm stainless wire for the coil? Soldering to it is not a problem, I am wondering if it has to be copper or what I have to change to get equivalent performance. I have the stainless, 316, and it will hold it's shape so I thought it could take more "abuse".
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Old May 31, 2012, 08:57 PM
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Australia, QLD, Brisbane
Joined Feb 2011
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Quote:
Originally Posted by markus123456 View Post
Not sure what you mean with "Coil centres" but I asume you refer to "Winding step (between centers)" or "s" as it's shown on jc opens page. If so, it should be 11.8mm for your case.

Based on my experiance, there is no way to "pre calculate" the other parameters to the degree you would like. As mentioned many times in discussions around 5.8Ghz CP antennas, tolerances and factors having influence are such that you can't do that. You have to build something, measure, then apply corrections. If you can't measure, build such that you can be sure to at least end with a useable result. Alas go wideband.

The definately most critical areas of a helical - provided you stick to the calculated parameters - are the feedpoint and the wavetrap. Precalculating them so as you end up with an antenna being highly resonant where you want it and then just build it to measure - impossible. So unless you have access to a vector network analyzer for the tuning process I recommend you to use a thicker wire ( 2mm for your frequency ) and mount the precalculated wave trap to the center of the first turns quarter.

HTH

Markus
Hi Markus,

Thanks for the response.

Yes winding step is what i was refering to.

I used .25 as the quarter wavelength instead of .23 so thats what gave me 12.9mm step rather than 11.8mm. What will the difference be at .25 (12.9mm) and why is it .23 rather than .25 (quarter wavelength?) Should i change it to 11.8mm (.23)?

I have access to a SWR meter so will 'attempt' tuning with that. With that in mind i would like to start with the right (or 'best' if there is no right) build measurements so that i can tune it with the wave trap.

I dont expect it to ever be 'perfect' but would like to go into this giving my self the best shot at getting close.

I am using 1.5mm copper coated PCB for the reflector, would it be possible to just reverse the pcb and lay the first quarter of a turn and the wave trap flat on the fiberglass backing, achieving an exact seperation of 1.5mm?? or does it need to be .4mm as per jcoppens calculator, or just as close as possible with out touching?

Thanks for any help.
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Old Jun 01, 2012, 01:29 AM
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hi all first post here i just built my first 5.8ghz 5 turn helical antenna and tested it yesterday and was only able to get a max range of 1.2km. Attached are the photos anyone recomend adjustments i can make to push it out a little further on 5 turns ive read through and seen people getting up to 3km with them.

Also attached a photo of my cl anyone able to tell me if its right hand polarized or left? i made my helical right hand polarized so if i got the wrong might explain why my range isnt that great.

Thanks every one in advance
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Old Jun 01, 2012, 01:47 AM
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Australia, QLD, Brisbane
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They are both RHCP so no worries there.

The only other thing i can see is the position of the wave trap. As far as i have seen it is supposed to be level with the reflector ???
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Old Jun 01, 2012, 02:37 AM
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thanks nogas ill give that a go. so does the wire have to be parralell or the wave trap? and they have to be as close as possible without touching the reflector i think i read some where
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Old Jun 01, 2012, 05:45 AM
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Quote:
Originally Posted by nogas View Post
Hi Markus,

Thanks for the response.

Yes winding step is what i was refering to.

I used .25 as the quarter wavelength instead of .23 so thats what gave me 12.9mm step rather than 11.8mm. What will the difference be at .25 (12.9mm) and why is it .23 rather than .25 (quarter wavelength?) Should i change it to 11.8mm (.23)?

I have access to a SWR meter so will 'attempt' tuning with that. With that in mind i would like to start with the right (or 'best' if there is no right) build measurements so that i can tune it with the wave trap.

I dont expect it to ever be 'perfect' but would like to go into this giving my self the best shot at getting close.

I am using 1.5mm copper coated PCB for the reflector, would it be possible to just reverse the pcb and lay the first quarter of a turn and the wave trap flat on the fiberglass backing, achieving an exact seperation of 1.5mm?? or does it need to be .4mm as per jcoppens calculator, or just as close as possible with out touching?

Thanks for any help.
The winding step is not that critical. You just have to make sure to stay at about that range as if it gets too small, the antenna all of a sudden will change to radiate like an omidirectional antenna to the sides.

Regarding the reversed reflector, you don't want that as the velocitiyfactor of the PCB material would come into play. Make the reflector bigger than the minimum size. I recommend around 5cm diameter, maybe a little more. The feed gap distance will be part of the tuning, so just adjust the wavetrap acordingly if like you say have acess to an SWR meter.

Markus
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Old Jun 01, 2012, 07:13 AM
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Thank you Markus. I adjusted the step to 11.8mm.

Just cut my reflectors out at 35mm, bugger! Back to the work bench.
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Old Jun 01, 2012, 05:38 PM
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Highland, CA, USA
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Quote:
Originally Posted by cyhyam View Post
for a 5.8 antenna are there any thoughts on using 1mm stainless wire for the coil? Soldering to it is not a problem, i am wondering if it has to be copper or what i have to change to get equivalent performance. I have the stainless, 316, and it will hold it's shape so i thought it could take more "abuse".
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Old Jun 01, 2012, 05:41 PM
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Quote:
Originally Posted by cyhyam View Post
For a 5.8 antenna are there any thoughts on using 1mm stainless wire for the coil? Soldering to it is not a problem, I am wondering if it has to be copper or what I have to change to get equivalent performance. I have the stainless, 316, and it will hold it's shape so I thought it could take more "abuse".
It does not have to be copper. HF energy, because of the so called skinn effect, travels on the surface of the conductor. I personally use silver coated copper wire because silver is know to be very very good for this type of application. However, if you manage the mechanical part of using stainless wire, that should work ok.

Markus
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Old Jun 01, 2012, 06:10 PM
Zephyr 66" Blunt
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New Zealand
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Apparently S/S sucks at radiating RF energy, trying to locate the table for the respective RF losses in different metals, I think gold was quite good

Mark
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Old Jun 02, 2012, 12:15 AM
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Originally Posted by IBCrazy View Post
A 5 turn helical has no business being on a tracker. This is why readymade only sells the 3 turn version (and that is pushing it too). I have been playing with some CP patches and also have the CP dual quad tutorial. These both work on a tracker.

Here's what I would do: sell the tracker and buy a diversity controller. Diversity is better than a tracker. Far more reliable. When these long range flight are done, what do they use? Diversity. There's a good reason for that.

-Alex
Sorry to dig this out of the grave, but I have your bluebeam whip set. I'm wanting to make a diversity system. I just bought the black cannon (10 turn) from urban drones. I'm wanting to but the helical on an antenna tracker. Do you think this is a good setup. Not real sure what my range limit is on my current radio. Turnigy 9x with frsky system. But I want to make sure I can reach it with clear video. I'm running ImRC 600 mw vtx and using my fatshark pred internal vrx for now.

Anyway would the Cl and helical (10 turn) be a good choice to get a well rounded diversity w/ tracker setup? I'm running the ezosd so I want to use it tracker feature.

Thanks
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Old Jun 02, 2012, 12:36 AM
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Yesterday I was sitting in my living room on the front side of my house. Had the helical (4.5 turn) pointing out the front window. Video hooked to my 32" tv was flyign around in front of the antenna with the tri, then decided to see how far I could go in the back yard (back side of the antenna. Wow I was surprised I had nearly perfect video through several double layer plaster walls (sheetrock over plaster) and the back wall of my house is 3 layers of sideing, vinyl over, concrete board, over wood. and I was able to fly a 150 ft away even at 8 o clock (if the helical was pointing at 12) with no real loss of video. I turned around and flew into the garden fence and broke a prop. But that was my fault.

Today I flew my CL with 5 lobe FAN on the rx in the living room. was pretty good, but not as good as the helical not even as good as the backside of the helical. Its pretty fun to fly like that though. I can do laps around my house. Now I jsut want to see if I can fly directly over the roof (3 stories up) with the fan antenna. The shingles might proof too much through two floors.

I clipped my power lines with the tri and it landed right on the CL breaking off the wires. Man these thigns are harder to fix than to make, all the lobes fell off when I tried to repair it!
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Old Jun 02, 2012, 04:40 AM
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Australia, NT, Katherine
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I have cut out a reflector from copper coated PCB. The hole saw puts a hole in the centre which is approx 7mm in dia, is this going to be a problem?
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Old Jun 02, 2012, 12:42 PM
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Originally Posted by nrg2go View Post
I have cut out a reflector from copper coated PCB. The hole saw puts a hole in the centre which is approx 7mm in dia, is this going to be a problem?
Nope, it should be ok.

Markus
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