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Old Apr 06, 2011, 08:46 AM
Videopilot
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United States, NC, Charlotte
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I would say pros are it is easy to make, and can easily be made for various gains. Cons are that is is more fragile and efficiency is much lower than the biquad.

I have found my 4 turn helical is excellent for 2 miles, and has terrific FOV.
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Old Apr 06, 2011, 08:56 AM
Engineer for Christ
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Amherst, VA
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Originally Posted by boopidoo View Post
What's the main pros & cons of this antenna vs the cp biquad?
Axial ratio and efficiency.

The CP double Quad has execellent efficiency at 95-98%, but the axial ratio is not great. Out of band rejection is only about 7-8db. This makes it Great for long range attempts but in close multipathing is still and issue.

The Helical is fairly inefficent. A 3 turn is only 80% at best. A 12 turn drops to 60% or less. However the axial ratio (ratio of linearity to circularity) is 2N+1/2N where N is the number of turns. 1:1 is perfect circularity with 26 db rejection. So even a 3 turn has a 9 db rejection.

The CP BiQuad (very different from my double quad) is the middle of the road. 85% efficient, but excellent axial ratio if you make your baluns right.

I personally fly a 4-1/4 turn helical as my antenna of choice. 2 miles is a walk in the park.

I just saw the Flite Test is building one of my helicals

-Alex
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Old Apr 06, 2011, 09:36 AM
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1. Is the helical going to get me better multipath rejection than the Skew Planar Wheel on my ground station? Though I have a cloverleaf on my plane, I've been running a regular linear Biquad and a SPW on diversity. The Biquad is excellent, but I'm having real trouble with that SPW and dealing with multipath (elements on the SPW are at a 45 degree angle and everything looks normal, but it's hard for me to be sure). I was going to try the linear BiQuad and an old linar patch on diversity later today to see how it does with the Cloverleaf.

2. For mounting, does the helical go up high or stay down low?
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Old Apr 06, 2011, 11:56 AM
Engineer for Christ
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Originally Posted by Infernal Bill View Post
1. Is the helical going to get me better multipath rejection than the Skew Planar Wheel on my ground station? Though I have a cloverleaf on my plane, I've been running a regular linear Biquad and a SPW on diversity. The Biquad is excellent, but I'm having real trouble with that SPW and dealing with multipath (elements on the SPW are at a 45 degree angle and everything looks normal, but it's hard for me to be sure). I was going to try the linear BiQuad and an old linar patch on diversity later today to see how it does with the Cloverleaf.

2. For mounting, does the helical go up high or stay down low?
The helical will absolutely dominate over the BiQuad with a cloverleaf on the plane as it has incredible circularity. In fact, placing the skew-planar wheel on the plane when using a helical results in slightly better signal than with a cloverleaf.

Helicals should be mounted high in the air for best results.

Circular polarization is a tool to help, but not a cure-all. Sometimes a little directivity is needed to help with multipath fading.

-Alex
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Old Apr 07, 2011, 08:35 AM
Pat K
The Netherlands
Joined Dec 2010
382 Posts
Hi Alex,
I've just performed a couple of flights with my setup:
- 200mW 5,8GHz FPVHobby combo (cam+Tx+Rx)
- stock frequency:5,945GHz
- Cloverleaf on the plane (according to your How-to)
- Helical 6turns (according to your How-to with Hecker transformer)

I'm flying over an industrial area not very dense (but with some antenna dishes on the roofs) where there is a nice large wild field in the middle where I can take off and land safely. I got very clear video up to ~700-800m and then the video fades out quite fast. From time to time, I get very strong glitches.
Do you think the range is what should be expected with such a setup or do you think there is room for improving the RF link? I haven't tested my antennas (frequency, SWR) yet but should be able to do it in the coming couple of weeks. I will try a SpinWheel on the Tx to see if it makes any difference.
Pat
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Old Apr 28, 2011, 09:25 PM
KF5LDN FPV Junkie!!!
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United States, TX, Lubbock
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I was considering the SP on my plane and a 4 turn helical and a SP hooked to my diversity. DOes that sound good or would I be better off with two helical antennae on the diversity Rxs?
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Old Apr 28, 2011, 10:38 PM
KF5LDN FPV Junkie!!!
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I also wanted to ask if polycarbonate would shift the frequincy the same as PVC? I have some sheets I'd like to use like the wood helix.

Or would it be better to just build the wood?
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Old Apr 28, 2011, 11:05 PM
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I'd just build a wooden one. I fly dual helicals. Works great, even through hills and houses. Ask me how many times I lost control due to that...


-Alex
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Old Apr 29, 2011, 01:27 AM
KF5LDN FPV Junkie!!!
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Originally Posted by IBCrazy View Post
I'd just build a wooden one. I fly dual helicals. Works great, even through hills and houses. Ask me how many times I lost control due to that...


-Alex
NICE! What gains are you using? I have started a 3 turn and I considered a 5 with it. would I be able to fly behind the array? I haven't built my tracker yet.

How many deg ofset is your array?
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Old Apr 30, 2011, 03:17 PM
Kiwi in Germany
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Germany
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Has anyone done any range testing on 5.8ghz and using this antenna? I would love to see what range people are getting on the standard chinese 200mw transmitter. Right now using a SPW and CL I get 1.1km easy but wind/being sick has stopped me testing the extreme range. Does anyone think that this would be worth the time to build for 5.8ghz (aka is there proof that this will work)?
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Old May 01, 2011, 10:30 PM
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Originally Posted by whakahere View Post
Has anyone done any range testing on 5.8ghz and using this antenna? I would love to see what range people are getting on the standard chinese 200mw transmitter. Right now using a SPW and CL I get 1.1km easy but wind/being sick has stopped me testing the extreme range. Does anyone think that this would be worth the time to build for 5.8ghz (aka is there proof that this will work)?
I built one and sent it to Jeffy who claimed it worked very well. I wound it around a wooden dowel rod. PM Jeffy and see what he has done with it.

-Alex
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Old May 01, 2011, 10:31 PM
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Originally Posted by Wizzard033 View Post
NICE! What gains are you using? I have started a 3 turn and I considered a 5 with it. would I be able to fly behind the array? I haven't built my tracker yet.

How many deg ofset is your array?
Mine isn't an array. It is two 4-1/4 turns on a diversity controller. Works great for me.

-Alex
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Old May 01, 2011, 10:44 PM
KF5LDN FPV Junkie!!!
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Originally Posted by IBCrazy View Post
Mine isn't an array. It is two 4-1/4 turns on a diversity controller. Works great for me.

-Alex
"Array" would probably be just me misunderstanding the term.

are they both pointed the same direction or offset? ANd do I remember right you don't use a tracker?
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Old May 02, 2011, 09:49 AM
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I have a tracker, but never use it. I had it on demonstration at the SouthEastern fly-in as it would track anyone's plane regardless of OSD.

I aim my antennas about 50 degrees apart. This increases my coverage.

-Alex
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Old May 02, 2011, 10:42 AM
Kiwi in Germany
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Germany
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Originally Posted by IBCrazy View Post
I built one and sent it to Jeffy who claimed it worked very well. I wound it around a wooden dowel rod. PM Jeffy and see what he has done with it.

-Alex
Jeffy hasn't done a range test with it yet. So far I am using a SPW and CL and I am getting 1.5km range pretty easy (made by markus). Need to think should I build a cp bi-quad or this one. Which is easier at 5.8ghz do you think to build.

Oh how do you make up your connections? Do I need to buy SMA pilers or is there a better/cheaper/easier way?
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