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Old Sep 27, 2012, 10:33 AM
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You could contact this seller: http://www.ebay.com/itm/17-shts-FR-4...item2574ada8c8

Maybe he can sell smaller amount...


BTW this is mine first bi-quad for 2.4 RC:









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Old Sep 27, 2012, 06:30 PM
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Quote:
Originally Posted by Martin Y View Post
I found that 1/8 wavelength minimum from the ends of the antenna element is good. So your 200 x 300 mm is spot on.
Excellent I'm going to order the cable and connectors.

Jack2010, I see your plastic cover. I was wondering if with vacuum forming it would not be possible to make a custom fit cover for it.
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Old Sep 29, 2012, 02:13 PM
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Albany NY
Joined Feb 2005
476 Posts
Ok certainly not the most conclusive test in the world but I finally got to try out my 2.4Ghz antenna. It was a bad day of low level clouds and mist so I didnt venture out very far but I generally wanted to get a idea of how this antenna performed.
I have to say it certainly beats paying money for a patch when you can build it yourself and it works just as well if not better. Not to mention it looks really cool.

FPV 2.4Ghz Antenna Test (6 min 18 sec)
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Old Oct 07, 2012, 08:57 AM
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What could happen if the element spacing was shorter?
Eager to make mine I ended up using a old whip antena, I've took it appart and use the connector. Problem was the cable was too short I made it for 980Mhz but still it fails short.

I tried it inside the house and works fine, even across walls where the other whip antenas I had would fail.
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Old Oct 07, 2012, 09:24 AM
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Shorter element spacing harms SWR (albeit only slightly) but actually increases F/B ratio. Thus it eliminates the lobe to the rear of the antenna.

-Alex
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Old Oct 07, 2012, 09:32 AM
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Originally Posted by IBCrazy View Post
Shorter element spacing harms SWR (albeit only slightly) but actually increases F/B ratio. Thus it eliminates the lobe to the rear of the antenna.

-Alex
I'll take care to avoid going much to the side/back of it. It will be used only with Multicopters so a lower F/B ratio would actually be better for me as I'll never go to far out.

Alex, Thanks a million for the time and dedication you put into sharing this things!

Btw a pic of the new toy! Had fun building it.



UPDATE: Just tested it... I want to break all my whip antenas I was using before. Even without the perfect sizes this one rocks!
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Old Oct 07, 2012, 12:13 PM
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My calculations for 1360mHz centered BiQuad are:

Full wave length
209.2mm(8.23622inch)
Section length
52.3mm(2.05905512inch)
Element spacing
26.15mm(1.029527559inch)
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Old Oct 08, 2012, 09:20 AM
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Cool builds. I do want to mention the possible hazards of heating up galvanized steel for the purpose of soldering the shielding. Known commonly as Metal Fume Fever, in small doses it won't cause permanent harm, but you may feel its symptoms. Just be careful.
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Old Oct 08, 2012, 02:11 PM
Foam Snow
South Africa, WC, Cape Town
Joined Aug 2011
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Holy smokes that was hard work

Mine did not come out as perfect as some of the others on here at all, but I was wondering if you all could take a look at it and see if I've made a catastrophic error somewhere.

Damn it's hard to solder something to a galvanized plate with a 25W soldering iron...

I couldn't find small nylon screws so I used wooden rods with epoxy.

I've soldered the shielding at the back of the plate in stead of the bottom of the front.
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Old Oct 11, 2012, 01:21 AM
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Gotta give out a big THANK YOU! to Alex. I built the BiQuad and it is selected over my L-com 8db patch by my diversity on anything less then a 45 deg advantage. I haven't been able to test the range till my UHF system arrives. What can I expect with 1280 800mw RV system? What would be a good companion antenna on a diversity, the patch seems redundant and weaker.
Thanks Again!
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Old Oct 11, 2012, 07:16 AM
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Range? I'm using a 4 biQuad phased array for a 50 mile link. So 25 miles for a single.

-Alex
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Old Oct 11, 2012, 08:05 AM
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Originally Posted by IBCrazy View Post
Range? I'm using a 4 biQuad phased array for a 50 mile link. So 25 miles for a single.

-Alex
My wish would be a thread about principals of phasing antennas, how one goes about it, I've seen a few of these arrays and it would be nice if I would be able to do them myself...Maybe you can teach me via PM or something if you don't want a thread be made here..
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Old Oct 11, 2012, 09:15 AM
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Originally Posted by IBCrazy View Post
Range? I'm using a 4 biQuad phased array for a 50 mile link. So 25 miles for a single.

-Alex
LOL. That's a can opened! When will that be added to the blog? I want one!
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Old Oct 11, 2012, 11:47 AM
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Phasing linear antennas is a walk in the park. All you need to know is the velocity factor of your cables and from there how to combine them into the array you like.

Let me explain:

2 50 ohm antenna in parallel is 25 Ohms. 2 50 Ohm antennas in series is 100 Ohms.

With odd multiples of 1/4 wavelength of coaxial cable (accounting for velocity factor) you can transform the impedance of any antenna. For example, if you use 1/4 wavelength of 75 Ohm coaxial cable to your 2 antennas in series (100 Ohms), you get 50 Ohms again. You have now phased 2 antennas.

Now for the quad array: We know 2 50 Ohm biQuads in parallel is 25 Ohms, right? Ok, well if we meet them together and use say, 3/4 wavelength of 50 ohm cable, the array now becomes 100 ohms. What good did that do? Simple: 2 100 Ohm loads is 50 Ohms and now you have a 4 antenna array.

With circular polarization, you actually need to rotate the firing order of the array where linear you phase it so it fires all at once. If you want a good example of a really well built 4 antenna CP array, look up TrueRC's "Gatling". 16dbic with an axial ratio of a perfect 1.0!

-Alex
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Old Oct 11, 2012, 12:17 PM
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Cool thanks, I kinda understand that, guess I have to build it to see for sure ..

Yeah thats exactly what I would like to achieve, a quad array of biquads at 2.4ghz for my rc link, and a quad array of crosshairs at 5,8ghz for video link.

So same principles apply for CP antennas, just the I need to rotate them like in the "crosshair gatling"? Would that work also for helicals I presume? (but these have no visual reference to rotate them?)?
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