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Old Mar 23, 2011, 10:40 PM
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IBCrazy's Avatar
Amherst, VA
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Mini-HowTo
Build a performance antenna for your LRS radio

This is my complete tutorial on how to build a turnstile antenna for your LRS system. Everything is explained. Even the theory and impedance plots are given.

You can find it all here: http://fpvlab.com/forums/showthread....tenna-tutorial

This video is the short and dirty:

Build IBCrazys Turnstile LRS antenna for FPV (4 min 33 sec)


Build, Discuss, Enjoy

-Alex
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Old Mar 23, 2011, 11:37 PM
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United States, CA, Galt
Joined Mar 2009
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Alex

i was looking at your turnstile antenna, I thought a 75 ohm phasing harness was required between the 2 dipoles.

like this:
http://www.west.net/~jay/turnstile.html

your antenna seems to be more of a modified biquad

Phil

i used to use them for wx satellite work years ago
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Old Mar 25, 2011, 11:23 AM
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i guess no comment...
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Old Mar 25, 2011, 12:43 PM
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That antenna is a different type of turnstile. The author used a 1/4 wavelength section of coaxial cable to obtain the phase shift where I used the reactive components of the wires. I tried using his method and it failed. The antenna performed very poorly until I tried using the reactances instead.

Does his work? Probably for 2 meters, but it doesn't work for UHF. At least not without a 1/4 wave section of 75 ohm coaxial cable to get the impedances to match up properly.

-Alex
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Old Mar 26, 2011, 04:37 AM
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thanks Alex,
i wasn't aware of the different way to acheive the same result, i'll have to build one and try it out.
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Old Apr 09, 2011, 11:10 AM
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Thanks for offering this video, i built myself one for my new plane.





Cheers, Kev.
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Old Apr 10, 2011, 08:50 PM
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Will servo wire work? Is there a certain gauge I need?
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Old Apr 10, 2011, 08:51 PM
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There IS such thing as a stupid question...

"Take 2 pieces of 18-22 AWG wire 15” (40 cm)"
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Old Apr 10, 2011, 10:28 PM
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Quote:
Originally Posted by Kmart View Post
There IS such thing as a stupid question...

"Take 2 pieces of 18-22 AWG wire 15” (40 cm)"
Wire thickness is critical. Wire has two properties R and X. together they create an impedance Z. As wire thickness changes, so does X and R, but X changes much more significantly where R is nearly constant. The X vectors of the two segments need to be opposed as closely to 90 degrees as possible at a point where their parallel equivalent is 50 ohms. This happens with an 18-22 AWG wire. Outside that range the X value changes too much and it loses it's phase shifting properties.

Simulating this is as easy as doing a frequency sweep of a simple Dipole in 4NEC2. Selects X/R plot and you will see what happens as you select different wire thicknesses.

-Alex
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Old Apr 10, 2011, 10:46 PM
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It would be interesting to do a ground range test with this antenna

like in this video

If it passes the test for the plane when it is in a dive or heavy climb it would be cool

or a tight turn

testing for diversity (1 min 6 sec)
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Old Apr 10, 2011, 11:57 PM
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So is 20awg the most ideal thickness? Or will anything from 18 to 22 work just fine?
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Old Apr 11, 2011, 12:13 AM
Just FPV'n
Orange County Ca.
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Whats the math behind this antenna?
Is it designed only for LRS?
How about the other frequencies??
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Old Apr 11, 2011, 07:20 AM
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The math is a complex impedance matching scheme. I designed it for 22 AWG wire. The reactance of that wire is fine for wire between 24 and 18AWG. 22 is optimal.

It works by phasing the reactive vectors 90 degrees apart. It is actually circularly polarized, but should not be used as such as the rotation shifts between the top and bottom of the antenna.

One element of the antenna is 52 +j54 and the other is 53-j52 if cut perfectly.

-Alex
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Old Apr 11, 2011, 07:28 AM
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this will work on any LRS..Dragonlink??...
using the welding wire (same wire used to make the cloverleaf ant.) should be ok..

thanks..
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Old Apr 11, 2011, 08:32 AM
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It will work with any LRS. I have some cables coming with MCX connectors for use with the Scherrer LRS.

Welding wire will work ok so long as it is .050 wire. Wire thickness is critical here.

-Alex
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