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Old Oct 24, 2011, 09:24 AM
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Ai77's Avatar
Deutschland, RP, Winningen
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Hi Nek,

first of all, you do not have to set the antenna on a pole upon the center of the tricopter.
The radiation is circular, so the copter will not influence too much, if the antenna is some centimeters away of metal or dielectric material and no part of the copter will shadow the line of sight.

Also it does not really have to be exactly perpendicular pointing up.
I found it is best to mount the antenna and VTX under the airframe center under the battery, pointing down.
In the center the battery will have the least impedance, only it's own without wires, and act as a little "shielding" from CPU noise. So EMI is surprising lesser than on any other place on the airframe between the motors. A raw thin pcb will shield even more and act as a "ground". Also the VTX does not interfere with GPS on top of the copter.

Another nice place is a guy wire between arms. A tricopter just calls for it! Make one side for RX and the other for VTX, for weight balace. Let the compact RX, VTX and their antennas hang on the wire.

As alway, ground ground ground! Connect everything metal on the airframe to the center ground point. It is done in reals airplanes, too. For good reasons!

cheers
Ai
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Old Oct 24, 2011, 09:52 AM
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^I agree. Under the copter is best.
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Old Oct 24, 2011, 12:09 PM
Nek
DIY O.G.
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French Polynesia, Windward Islands, Faaa
Joined Nov 2002
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Wow, thanks a lot for all the great suggestions!!!

Maybe I had more range but could not properly test it. Will do on my next set.

Here is a recap of what I should try changing, will be sure to post again with the results!

1- Everything grounded. Looks like I am good there, anything metal grounds to my center power plate. Frame is 100% wood and nylon.

2- I really like that guy wire idea, but it would have to be very taunt to not have any play with movements right? Definitely something I want to look into. Spreading out the weight throughout the copter seems to be key for stable flight! Thanks for the great idea!

I was thinking about using some small carbon fiber rods as guy wire. Would that be bad for the microwaves? If I tape or shrink tube the rods would that fix it?

3- Will make my antenna wires as short as I can. Right now I do not have access to RG317, I ordered a few cables with straight and 90 SMA connectors but it will be some weeks before I get them.
Should I try to make a new CL and SPW with something like 2-3mm of cable left after the connector sleeve, or should I try to solder it directly to the connector?

4- After doing more reading I remember IBCrazy saying that hot glue could shift the signal by a couple %. I guess changes will be even more dramatic at the 5.8GHz range. I guess I could do without but it seems the base of the antenna soldered to the antenna cable shield would be very weak. What else could I use to make it a little more robust?

5- Is it OK to paint the antenna with electronics plastic spray, looks like a very light coat, some sort of conformal coating.

I will be redoing my antennas today with some thicker wire if I can find it. I used something around 22-20 AWG single strand wire and it looks a little thin compared to other 5.8GHz CP antennas I see in this thread. 0.8-0.9mm is a good size to look for right? It is hard to know which design in this thread to exactly copy and I could not find details for IBCrazy's 5.8GHz version. So many different ways to cut, bend and solder to the coax!

Thanks gain for all the great insight and I will give it another go!
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Old Oct 24, 2011, 10:02 PM
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Just did a 1.28 one, using the stock antenna bases. I just added a little liquid electrical tape to keep the 2 feed points from touching, they are very close. I plan on adding some clear coat next.
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Old Oct 24, 2011, 11:51 PM
Nek
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French Polynesia, Windward Islands, Faaa
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Since right now RG174 is all I had I stripped it all the way to the bare rotating shield.

Here are a few pictures of the build of the 5.8GHz skew planar wheel.



I used 1.34mm copper wire and it seemed to work just nice for making the bends.

Please let me know if that one looks better. I will start working on my cloverleaf.

Also is it better to strip one of the stock rubber duckys, or I might just as well use the connector from the RG174 as I did?

I also have this plastic spray and was thinking of using it (http://www.taerosol.com/prf_products/27) but it says that it is insulating as well, so that would be bad right? I need to find a good coating fast as things rust super fast here, I only have a few hours ahead of me lol

Thanks again for the help!
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Old Oct 25, 2011, 12:43 AM
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Poway, CA USA
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Originally Posted by IBCrazy View Post
That looks more like an elliptically polarized antenna rather than a circular one. CP isn't done by making round shapes. It is done by vector phase coordination.

I have abandoned the CP patch idea. Patches are sub-optimal antennas IMHO. L-COM and ReadyMadeRC sell 8db CP patches that work ok. I was going to sell CP patches at one point, but the performance did not meet my requirements.

-Alex
Well with that knowledge I won't worry about matching it then and just get started building, my plan was skew planar on the plane, a cloverleaf and helical on a tracker on diversity for the rx, sound reasonable? Thanks. Kirk.
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Old Oct 25, 2011, 12:55 AM
Nek
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Originally Posted by atckirk View Post
Well with that knowledge I won't worry about matching it then and just get started building, my plan was skew planar on the plane, a cloverleaf and helical on a tracker on diversity for the rx, sound reasonable? Thanks. Kirk.
From what I understand, you want cloverleaf on the plane, with the skew planar and helical on the rx side with your diversity and tracking.

Edit: just done with the 5.8GHz cloverleaf, looks good?

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Old Oct 25, 2011, 03:46 AM
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Originally Posted by Nek View Post
From what I understand, you want cloverleaf on the plane, with the skew planar and helical on the rx side with your diversity and tracking.

Edit: just done with the 5.8GHz cloverleaf, looks good?
Nek,

Your antennas look good. The angle of attack of the CL seems a bit flat though. Don't expect super long range but if all else is ok, and if you were lucky enough to be at least near the frequency you operate them you should be good for 1-2 km of range. Maybe you should experiment with changeing channels a bit as the sky-rf based units virtually go from mid 5.6Ghz all the way up to 5.9Ghz with a big gap in between around 5.8Ghz.

Markus
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Old Oct 25, 2011, 03:50 AM
Nek
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Originally Posted by markus123456 View Post
Nek,

Your antennas look good. The angle of attack of the CL seems a bit flat though. Don't expect super long range but if all else is ok, and if you were lucky enough to be at least near the frequency you operate them you should be good for 1-2 km of range. Maybe you should experiment with changeing channels a bit as the sky-rf based units virtually go from mid 5.6Ghz all the way up to 5.9Ghz with a big gap in between around 5.8Ghz.

Markus
Thanks for the pointers Markus!

What do you mean by the angle of attack? The 45deg of the lobes?

Also I am on the airwaves bandwidth with my fatshark and immersionrc stuff. From what I understand video quality is slightly better, but you need a stronger VTx like 600mw to compensate for the loss of 5db in the VRxs gains. Sounds about right?

So maybe it was a mistake but I shot for the lowest possible channel, 5740MHz to have the biggest possible antenna. If I am off I hope it is higher than lower

I will do some basic range tests with only the VTx on a long road tomorrow and see how it goes and compare with my older ones.
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Old Oct 25, 2011, 05:24 AM
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Originally Posted by Nek View Post
Thanks for the pointers Markus!

What do you mean by the angle of attack? The 45deg of the lobes?

Also I am on the airwaves bandwidth with my fatshark and immersionrc stuff. From what I understand video quality is slightly better, but you need a stronger VTx like 600mw to compensate for the loss of 5db in the VRxs gains. Sounds about right?

So maybe it was a mistake but I shot for the lowest possible channel, 5740MHz to have the biggest possible antenna. If I am off I hope it is higher than lower

I will do some basic range tests with only the VTx on a long road tomorrow and see how it goes and compare with my older ones.
Yes, the 45 degrees angle, wich with the CL can be slightly more even (47 or so). Shooting for a frequency is a honerable attempt, but not really much more without the measuring equipement on 5.8G.

With the immersion RC stuff you have the advantage that they don't have this "gap" around the center of 5.8G. When makeing your own antennas, you should shoot for the center frequency as you WILL be off by 100 - 200 Mhz PER antenna and if you have bad luck in both directions. Make the lobes of the CL slightly longer (about half a millimeter) as the CL otherwise will be 100 to 200Mhz above the SPW.

The wire thikness you use is on the upper edge for 5.8G. I use 6mm, but if I were you I probably would use 1mm. Thicker wire makes it harder to work with precise lenghts and bending etc. on those high frequencies. The good thing is that it tends to make the antenna more wideband thus chances are higher to have a better frequency response where you will operate them. This however has the price of smaller sensitivity but again, you have to make compromises when building antennas at 5.8G just to measures.

Markus
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Old Oct 25, 2011, 07:20 AM
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looks good, Nek.

did you have to correct the base segment for the diameter of the coax cable?

the feedpoint is a few mm above the base, but the base does not meet at single point, but around the circumference of the coax instead. i'm wondering if you made the straight base segment about 1-2 mm shorter to account for the coax?

alternatively, is it better to solder the base segments into a single point and then solder that to the coax from one side? this would keep the dimensions of the CL/SPW somewhat more true.

thanks
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Old Oct 25, 2011, 07:25 AM
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looks good, Nek.

did you have to correct the base segment for the diameter of the coax cable?

the feedpoint is a few mm above the base, but the base does not meet at single point, but around the circumference of the coax instead. i'm wondering if you made the straight base segment about 1-2 mm shorter to account for the coax?

alternatively, is it better to solder the base segments into a single point and then solder that to the coax from one side? this would keep the dimensions of the CL/SPW somewhat more true.

thanks
As long as it's within reasonable limits there is no need to correct for this.

For 5.8Ghz, bottom feed is the way to go. Side feed introduces issues with the fresnel zone on 5.8G due to the small size of the antenna compared to the (in relation to the antenna) bulky cable.

Markus
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Old Oct 25, 2011, 09:18 AM
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Chicago, IL USA
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Flew Alex's Cloverleaf VTx with Skew Planar Wheel and two 9.5dbi helicals for VRx on two diversity stations at 1280mhz...there's FPV view video in middle of footage, but NO DROPOUTS! and only blocks from some of the heaviest RF around!

http://vimeo.com/31081513
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Old Oct 25, 2011, 09:32 AM
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Originally Posted by Nek View Post
From what I understand, you want cloverleaf on the plane, with the skew planar and helical on the rx side with your diversity and tracking.
Oops I misspoke, I get the cloverleaf and skew planar mixed up since they look similar, Cloverleaf for transmitting, skew planar for receiving, Check..Thanks. Kirk.
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Old Oct 25, 2011, 10:57 AM
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Quote:
Originally Posted by AdamChicago View Post
Flew Alex's Cloverleaf VTx with Skew Planar Wheel and two 9.5dbi helicals for VRx on two diversity stations at 1280mhz...there's FPV view video in middle of footage, but NO DROPOUTS! and only blocks from some of the heaviest RF around!

http://vimeo.com/31081513
I'm glad you are enjoying your equipment. I remember that helical of yours was giving me all sorts of trouble tuning it just right. Sometimes they're easy, other times it's hard, but it's all worth it when the palne takes to the sky

-Alex
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