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Old Feb 24, 2011, 03:27 AM
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Wizzard033's Avatar
United States, TX, Lubbock
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Quote:
Originally Posted by IBCrazy View Post
I find the cloverleaf (3 blade) is a bit easier at 5.8GHz. It performs just as well as the skew-planar wheel in my tests. You need to compensate for the added length given from the coaxial cable sticking out of the connector by shortening the lobes a bit.

-Alex
So if using a length of coax you need to reduce the length of the lobes on the 5.8G Would it also be true for 1280Mhz? If so why couldn't you use a length of coax on the 1280Mhz and the 900Mhz in order to make the antenna size a bit more manageable?
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Old Feb 24, 2011, 03:53 AM
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SW England
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I always use coax in multiples of a half wavelength at the frequency in use, also allow for the velocity factor of the coax.
This way, there is less chance of the coax becoming a matching transformer and the potential for current flow on the cable itself.

Nigel.
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Old Feb 24, 2011, 01:14 PM
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Interesting TY Sir! I'll give that a try this time.

When using the coax is there an orientation to the coax that is preferable?
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Old Feb 24, 2011, 05:47 PM
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I can't do a full half-wavelength. My cables are not long enough. Would a quarter work? What is the velocity factor? Would it be better just to put it as close to the connector as possible?
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Old Feb 24, 2011, 08:11 PM
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Quote:
Originally Posted by Devonboy View Post
I always use coax in multiples of a half wavelength at the frequency in use, also allow for the velocity factor of the coax.
This way, there is less chance of the coax becoming a matching transformer and the potential for current flow on the cable itself.

Nigel.
Would you mind if I take exception to this? If the antenna is built properly and resonates at the proper 50 ohm impedance, then a 50 Ohm matching stub will result in the exact same impedance.

Remember your equation:

Zin = Z0^2/ZL

If Z0 = ZL = 50 Ohms then Zin = 50 Ohms.

Thus you can make the cable any length you want without harming the impedance match.

-Alex
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Old Feb 24, 2011, 11:57 PM
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I have some 20ga steel for picture hanging I'm going to attempt some antennae some time this weekend
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Old Feb 25, 2011, 03:06 AM
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Quote:
Originally Posted by IBCrazy View Post
Would you mind if I take exception to this? If the antenna is built properly and resonates at the proper 50 ohm impedance, then a 50 Ohm matching stub will result in the exact same impedance.

Remember your equation:

Zin = Z0^2/ZL

If Z0 = ZL = 50 Ohms then Zin = 50 Ohms.

Thus you can make the cable any length you want without harming the impedance match.

-Alex
I'm not disagreeing Alex, and that is good theory in an ideal situation.
In the real world, all things are not equal and less than perfect.

It is so easy to calculate and use a length of coax in a multiple of half wavelength, why not just do it?

Nigel.
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Old Feb 26, 2011, 04:00 PM
Happy FPV pilot
lucianozan's Avatar
Italy
Joined Feb 2009
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Quote:
Originally Posted by IBCrazy View Post
I find the cloverleaf (3 blade) is a bit easier at 5.8GHz. It performs just as well as the skew-planar wheel in my tests. You need to compensate for the added length given from the coaxial cable sticking out of the connector by shortening the lobes a bit.
-Alex
Following MarcAntonio, Alex, Devonboy and Mikey-flies suggestions I've modified the Skew Planar. Cutted the 4 lobes that now are 2mm shorter and soldered on the connector side. I have reduced the coax cable that was sticking out and now the coax is soldered to the antenna as soon as it exits from the connector. The geometry is not Star Trek and can be improved in the next prototypes.

I've also built a Cloverleaf for the VTX ...and it's really easier to do. Following Devonboy suggestion I've kept the antenna a little far from the VTX, soldering it on top of a little coax cable (half wavelength long).

Today I've done the same flight tests on the same course and the results are pretty good! I've got my target 1000m (0,62 mile) with video much more clean and with less disturbance even when the model was banking.

Here a little video. The first part of the video is done with the whip standard antenna. In the second part the same course is done with the new IBCrazy antennas. I think that the difference is evident. I've left all the sounds (forgot to switch off the vario) so you can better appreciate the disturbance....or the silence!

Thank you Alex for your tutorial and thank you all for your support!

Luciano

http://www.youtube.com/watch?v=-_wXTwjepsk
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Old Feb 26, 2011, 07:43 PM
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Awesome antenna! Well done! Both of them look incredible. Now you need to try a helical!
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Old Feb 27, 2011, 01:21 AM
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@IBCrazy or anyone with the knowledge

Will 20ga steel picture hanging wire be good?
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Old Feb 27, 2011, 03:22 AM
O <- this a ground loop
Japan
Joined Nov 2010
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Quote:
Originally Posted by Wizzard033 View Post
@IBCrazy or anyone with the knowledge

Will 20ga steel picture hanging wire be good?
It won't solder well but in terms of thickness it should be fine.

Thickness is best judged by being thin enough to bend in making but thick enough to not deform at speed due to oncoming air flow.

Ren
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Old Feb 27, 2011, 03:25 AM
O <- this a ground loop
Japan
Joined Nov 2010
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Quote:
Originally Posted by lucianozan View Post
Following MarcAntonio, Alex, Devonboy and Mikey-flies suggestions I've modified the Skew Planar. Cutted the 4 lobes that now are 2mm shorter and soldered on the connector side. I have reduced the coax cable that was sticking out and now the coax is soldered to the antenna as soon as it exits from the connector. The geometry is not Star Trek and can be improved in the next prototypes.

I've also built a Cloverleaf for the VTX ...and it's really easier to do. Following Devonboy suggestion I've kept the antenna a little far from the VTX, soldering it on top of a little coax cable (half wavelength long).

Today I've done the same flight tests on the same course and the results are pretty good! I've got my target 1000m (0,62 mile) with video much more clean and with less disturbance even when the model was banking.

Here a little video. The first part of the video is done with the whip standard antenna. In the second part the same course is done with the new IBCrazy antennas. I think that the difference is evident. I've left all the sounds (forgot to switch off the vario) so you can better appreciate the disturbance....or the silence!

Thank you Alex for your tutorial and thank you all for your support!

Luciano

http://www.youtube.com/watch?v=-_wXTwjepsk
Luciano,

bit worried about your VTX placement right next to your GPS.

If you fly any kind of distance and have need for accurate GPS (plane down locating or RTH etc) then you would be best to seperate them out of principle even if the frequencies and harmonics are not a real factor.
Call it best practices if you will.

Ren
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Old Feb 27, 2011, 03:58 AM
Happy FPV pilot
lucianozan's Avatar
Italy
Joined Feb 2009
148 Posts
Quote:
Originally Posted by devfor View Post
...bit worried about your VTX placement right next to your GPS.

If you fly any kind of distance and have need for accurate GPS (plane down locating or RTH etc) then you would be best to seperate them out of principle even if the frequencies and harmonics are not a real factor.
Call it best practices if you will.

Ren
Hi Ren!

Thanks...you are right! I was worried too about the GPS placement ...and in the first time (with 2.4Ghz kit) I put it far from VTX. Now with this 5.8Ghz kit I've built an FPV pod that I can move among models so I need to keep everything pretty close...well... at 5.8Ghz the VTX seems to have little effect on GPS. It finds satellites very soon (10-11 sat during flight) and the info on OSD look to me quite accurate (compared with other barometric telemetry sensor).

BTW on my MaxiSWIFT with 5.8Ghz kit I've put the GPS very very far from VTX....best practices...you never know...

Luciano
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Old Feb 27, 2011, 04:03 AM
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Denmark, Capital Region of Denmark, CPH
Joined Mar 2006
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First, my apology if this has been asked before, but could I benefit from using the skew planar or the cloverleaf on my Spektrum transmitter?
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Old Feb 27, 2011, 04:09 AM
Happy FPV pilot
lucianozan's Avatar
Italy
Joined Feb 2009
148 Posts
Quote:
Originally Posted by IBCrazy View Post
Awesome antenna! Well done! Both of them look incredible. Now you need to try a helical!
Thank you Alex! I understand that helical are pretty directive and as I normally fly 360 around me looking for thermals I believe that a non directive antenna should be better....is it correct?

Next tests will be a new Cloverleaf mounted at 90 under the FPV T-REX450 boom. With the standard whip in the same position I get a lot of disturbance when the heli is flying low facing the ground station ...if I land a bit far sometimes I even loose the video signal. I'll let you know!!!

Luciano
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