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Old Feb 09, 2011, 06:49 AM
Cape Cod
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Alex,

Congrats on getting the Diawa. I did not realize they made one for our needs. I just bought a Bird with the proper elements on ebay. Got a couple of "N" to sma adapters and am anxious to see the actual output of my 900mhz Tx's.

Have you had a chance to evaluate the Saw filter mod on your 900mhz Rx?

If it would just warm up here maybe I could fly.......


Tom
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Old Feb 09, 2011, 01:01 PM
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Old Feb 09, 2011, 01:06 PM
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What is that ball made for? I am curious as to what kind of shop to look for it at. I looked at a craft store but didnt see anything like it.

And if the foam doesnt affect it, couldnt it also just be put inside the fuselage, provided the plane is large enough?
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Old Feb 09, 2011, 01:28 PM
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Old Feb 09, 2011, 01:40 PM
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Quote:
Originally Posted by tom3holer View Post
Alex,

Congrats on getting the Diawa. I did not realize they made one for our needs. I just bought a Bird with the proper elements on ebay. Got a couple of "N" to sma adapters and am anxious to see the actual output of my 900mhz Tx's.

Have you had a chance to evaluate the Saw filter mod on your 900mhz Rx?

If it would just warm up here maybe I could fly.......


Tom
The SAW mod helped some, but not much. I got better results with a Lawmate RX on the helical antenna than I did with my modded 1.3GHz standard RXs. Unfortunately the Lawmate does not play nice with the skew-planar wheel.

900MHz TX's are VERY sensitive to having the proper antenna. The output begins to drop immediately after the SWR drops below 1.2. I just tested my first ever Vee antenna and found the SWR was about 1.3 or so which dropped the TX output to 400mW. I tested it with my new Vees and got a VSWR of 1.05 and an output of 500mW at 12VDC.

-Alex
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Old Feb 09, 2011, 02:36 PM
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Are your newer Vees more dimensionally accurate?
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Old Feb 09, 2011, 09:47 PM
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No. Every Vee I have sold is the same. I just tested my first ever Vee antenna which was made long before I started selling them. Every Vee I sold is made for SWR of 1.2 or less.

-Alex
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Old Feb 09, 2011, 11:05 PM
Cape Cod
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Alex,

Thank you for the comments. I got both the bird and the 400-1000mhz 5 watt element today. I tested the 500mw 900mhz Vtx I had been using in my EZ. It measured, with a bird 50ohm load, 2.6 watts output. I looked at it again and that is what it read. It must be the element or the watt meter. I did buy another 1 watt 400-1000mhz element on ebay. I am off to work for a week so will test it when I get home.


Tom
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Old Feb 11, 2011, 06:18 AM
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Old Feb 11, 2011, 06:35 AM
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Nice work, Micheal! This confirms my suspicion that the antenna has some polarizaion in the opposite direction. Do you have any of the source files for 4NEC-2?

If I send you the details of my cloverleaf antenna, (which is very similar to the skew-planar wheel but with one less lobe) do you think you could model it? It is basically a 3 lobe skew-planar wheel over a ground plane .2 wavelengths away.

-Alex
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Old Feb 11, 2011, 06:35 AM
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So, I worked some math and played with Excel. A quarter of an SPW antenna will be auto calculated now. Copy, paste and rotating can be used in the 4nec2 geometric editor to complete the antenna.

OMM, what you think?

An example, calculated for 1240MHz:
Excellent. I'll give you an A+ if the element lengths and the two key angles are defined as variables inside of 4Nec2. Be sure that the one angle defining the 1/2 wavelength arc can go beyond 90 degrees. With those variables you will be able to do auto optimizations.

Can you show the RHCP vs LHCP plots in 3d Color mode?

OMM
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Old Feb 11, 2011, 06:42 AM
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Old Feb 11, 2011, 06:47 AM
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For now calculation for now is only done in Excel. Phi and Theta angle for the hot Lambda/4 element is variable.

What other plots you want to see? The above show RHCP and LHCP gain.
I would like to see the RHCP and LHCP plots in 3d like this set (from my CPOD antenna):





OMM
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Old Feb 11, 2011, 07:02 AM
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Old Feb 11, 2011, 07:05 AM
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Awesome! Excellent work Micheal! Absolutely incredible!

Do you think you could model a 3 lobe skew planar wheel over a ground plane 0.2 wavelengths away? I have been considering this as an RX antenna. It is far easier to build than a quadrafiliar helix.

-Alex
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