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Old Oct 27, 2010, 02:14 PM
The Fixer
Martin Y's Avatar
Canada, ON, Milton
Joined Jan 2009
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Quote:
Originally Posted by techspy View Post
I will be building this one soon. Couple questions... Does painting (light spray paint) have any discernible effect on performance? I am thinking flat black but would there be any benefit to a chrome/copper type paint?

Thanks
Painting the antenna element will effect it a bit. You can paint the reflector any colour but use either conformal spray or clear on the element. Plus it depends whats in the paint.
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Old Oct 27, 2010, 03:01 PM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by Martin Y View Post
Painting the antenna element will effect it a bit. You can paint the reflector any colour but use either conformal spray or clear on the element. Plus it depends whats in the paint.
So long as he keeps it off of the antenna feedpoint, there will be no noticeable effect. Since the paint isn't supporting the element against the reflector, the capacitive effects of an insulator are neglegible.

That said, I am assuming he's spraying it with a thin layer and not building it thick. 1-2 mils of paint will not make any difference. Human manufacturing tolerances make far more of a difference.

-Alex
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Old Oct 27, 2010, 04:00 PM
UAV Pilot
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sweden
Joined May 2007
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Really nice! I have a Spektrum (2.4) and my TX is in 1.2/1.3 Ghz band...

An external SMA connector on the DX7 to hook up antenna to would be really cool - using Interface Cable RP-SMA to U.FL

I assume it's just to solder a connector to the other end of the Coax ?


(I have plans for a really cool - not seen yet tracking device)

//UndCon
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Old Oct 29, 2010, 08:19 AM
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Just thinking out loud , what happens if you make it a tri quad on a more oblong reflector ?
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Old Oct 29, 2010, 08:35 AM
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Amherst, VA
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High impedance and thus poor performance. You can make a double biquad and get 13dbi gain or a stacked double quad and get 14 dbi. The double biquad is bigger and easier. The stacked double biquad has a parasitic element and thus it is a bit harder to make, but it is the same size as the biquad. It's basically a biquad Yagi

-Alex
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Old Oct 31, 2010, 12:50 PM
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Bemidji, MN
Joined Dec 2003
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Very nice Alex!

I'll be building one this week!

You certainly have given a lot back to the FPV community.

Thank you!

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Old Oct 31, 2010, 01:57 PM
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Well decided to build a Bi quad and it is not so hard ,
But
I found my self a piece of 1mm aluminum and it is virtually impossible to solder to ....

So my tip is do not use sheet aluminum stay with copper or steel .....


Nick
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Old Nov 01, 2010, 10:49 AM
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Great news to report

I built the BiQuad antenna this weekend using variations of the IBCrazy and Talajouy designs.

http://www.rcgroups.com/forums/showthread.php?t=1301126

I made this BiQuad for 1280mhz and used a SunSky 1.2ghz 800mW transmitter and IBCrazy Vee antenna.

Placing the transmitter on one side of my very dense house and my receiver at the other end of the house, I got the following RSSI readings.

Stock rubber ducky antenna on both transmitter and receiver - 63

Transmitter with Vee antenna and stock receiver antenna - 85

Transmitter with Vee antenna and BiQuad antenna (in phase) - 97 rotate BiQuad 90 degrees (out of phase) = 86
++++++++++

I used 22ga sheet of sheet steel from Home Depot cut to 9.17" square. I used 10ga electrical wire for the sections (I took one long piece and bent it as a single wire) and bent them to 2.29" per section.

One question I have is, the designs call for sections of 2.29". I bent the wire at 2.29" but after the bend was made, the outer dimension was ~ 2.40". Which dimension do you bend to? an inner dimension of 2.29" or outer dimension of 2.29"?? Whatever it is, my antenna worked great.

I made slight changes to the IBcrazy design by cutting 6 spacers out of 1/4" wood dowels and sanding them to 1.15" I ended up epoxying the spacers to the steel reflector (worked well) I used hot glue to secure the antenna to the top of the spacers (also worked well).

I used RG174 wire with an SMA connector but try to keep it short, I noticed that the longer the distance from the SMA connector to the BiQuad antenna, the lower the RSSI reading. I noticed that looking at Talajouy's post that he connected the receiver directly to the back of the center feed, I think that is optimal.

I am still waiting for my eBay 13dbi yagi to see if that will beat this BiQuad but I bet it'll be close.
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Old Nov 01, 2010, 10:53 AM
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On a funny but truthful note, last weekend at my Gf's house they were pissed that they couldnt watch tv cose the antenna they bought, seems to be some kind of patch with an amp didnt work properly and the picture was worse than poor.

Just for fun I grabbed a bit of "wrapping" thin wire that was keeping one of the antenna cables and quickly shapped a biquad. Literally truck it to the plug on the back of the Tv and it had the best reception ever, I was amazed! ahahah great stuff.
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Old Nov 01, 2010, 11:11 AM
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Hi IB, for long distance, which one is better?

Patch, Biquad or Yagis?

Thanks a lot, your tutorials are awesome.
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Old Nov 01, 2010, 11:24 AM
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kubiaks - Nice work! Very nice antenna! I can't wait to hear your results flying it. On the dimensions, the lengths should be from the center to center. You built yours correctly.

FabioBrazil - It all depends on what your goals are. There is no "best" antenna. The antenna determines the propagation pattern onf the recieved wave. They all cover the same area, but some direct it better than others.

The Biquad is a longer range antenna and therefore has a narrower beam than my fast patch. I also prefer it to a Yagi as Yagis can degrade the signal with humidity and other conditions.

I need to build a BiQuad for my homebrew antenna tracker I got the control circuit all soldered up. Now I need to build another Biquad and make the turn table

-Alex
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Old Nov 01, 2010, 11:41 AM
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How about 30dbi for the really long range aficionado's using a biquad and old satellite dish with offset feed...

http://www.trevormarshall.com/biquad.htm

Only problem is, it only has a 4 degree beamwidth (aside from it's physical size!) but hey, at 10+ mile out, that 4 degree is quite wide.

Nigel.
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Old Nov 01, 2010, 03:44 PM
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That is quite possible to do. You can use any satellite dish, really. The focal point must be at the rear of the antenna, not the front. Admittedly, I have no idea why this is.

I will be building a stacked BiQuad (~14 dbi) later. This can also be used as a feed for a dish and will increase the gain even more

-Alex
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Old Nov 01, 2010, 05:43 PM
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The dish needs to be offset fed as well, because if it's focal point is central, the biquad's reflector (and support arm(s)) will interfere with all those waves you are desperately trying to focus onto the biquad feedpoint.

Could you add the sizes for those of us on 5.8GHz in your 3rd post.

Quad element lengths = 12.9mm each leg
Element from reflector = 6.5mm
Reflector size = 52mm square

Works for me


Also, looking at your figues for 2.4GHz "sectional length" in your 3rd post, you have:
2.4GHz = 1.197/30.41cm

Should be 3.04cm (30.4mm)

Keep up the good work.

Nigel.
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Old Nov 01, 2010, 07:30 PM
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Bemidji, MN
Joined Dec 2003
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Hi Alex,

Again thanks for the great BiQuad information. Mine is about 90% done, but I need a few more nylon nuts to finish it up.

Concerning your home brew antenna tracker, I was thinking along the same lines. I assume you're thinking pan only. Tilt seems rather irrelevant unless you're going for very high altitudes or live in the mountains like Trappy! For us flatlanders, pan should be just fine.

Concerning your schematic. I'm not quite sure what the purpose of the 2k and 390 ohm resistors is on the output of the LM393 op amp??

I haven't looked at an NE555 spec sheet for quite a few years. Is there an easy way to get it to change duty cycle based on a varying input voltage? I don't recall that being a feature of the chip. I'll have to get a data sheet from Digikey on the 555 and check it out. At any rate, this scheme should work with the addition of a circuit to convert the varying comparator voltage to a pulse train with varying duty cycle.

To make it work in application, you'll need two identical high gain antennas (Patch, BiQuad, or Yagi) pointed anywhere from 10 to 30 degrees apart horizontally depending on antenna beam width, etc.

All this being said, the more complex GPS based systems do have their advantages. I could see this system tracking a side lobe and getting confused. A GPS based system won't be fooled like this.

You should start another thread so we can begin discussing this. I like the idea of a simpler antenna tracker without all the complexity of GPS, return link, etc.

The big question is: Will it track well? It should be a fun experiment!

Bill

Quote:
Originally Posted by IBCrazy View Post
kubiaks - Nice work! Very nice antenna! I can't wait to hear your results flying it. On the dimensions, the lengths should be from the center to center. You built yours correctly.

FabioBrazil - It all depends on what your goals are. There is no "best" antenna. The antenna determines the propagation pattern onf the recieved wave. They all cover the same area, but some direct it better than others.

The Biquad is a longer range antenna and therefore has a narrower beam than my fast patch. I also prefer it to a Yagi as Yagis can degrade the signal with humidity and other conditions.

I need to build a BiQuad for my homebrew antenna tracker I got the control circuit all soldered up. Now I need to build another Biquad and make the turn table

-Alex
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