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Old Mar 02, 2011, 10:34 AM
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Derek_S's Avatar
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You want the whole antenna or just wood? Pm me or email me your address. I sent you a message and some drawings.
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Old Mar 02, 2011, 10:55 AM
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Derek, If you are going to make these, you need a repeatable match. I will come up with a match that works with this perfectly so there is no guess work. We'll go with a tapered match to make it easy to replicate. It will also scale better.

I got your drawings and updated them a bit. If you can cut me a sample or two for 5 turns, I will design a tapered match for you, build up one antenna and send it back to you ready to go with perfect SWR. I will also send you some tapered matching stub samples to build more of your own.

In addition, send me a couple of the antennas you have already made, I'll let you know how close you came to the mark, tune it for perfect SWR and send it back to you

-Alex
KJ4RIV
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Old Mar 02, 2011, 02:16 PM
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I would like to contribute to this. I can build a 2414 MHz antenna (I will build 2) if we can settle on the correct dimensions for the various parts including the tapered match. I can then send them to Alex for testing. I would like to make both 5 and 7-8 turn versions, perhaps 2 of each. I think I can use scraps of pcb board for the ground planes, or we have lots of aluminum or sheet metal lying around our shop at work.

It might help me get started if someone could share their source for the cables and connectors as well so I can get an order placed.

I also have a spare IntelligentRC 2.4 500mW tx that we can use for testing if necessary, given that my TS2 did a dirt dive last weekend. I don't know how much 2.4 GHz gear Alex has. I also have a spare RX.

-Tom
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Old Mar 02, 2011, 02:27 PM
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I will send you cables if you need them. Everyone takes forever to ship other than a select few. I can have them to you in 3 days - free.

Do you have a drawing for your design? if so, send it to me at gadgetinventor <at> yahoo and I will take a look at it and verify the dimensions. You can use the equations on the first page.

Also, use galvanized steel for the ground plane. Aluminum won't solder.

@Derek - I made another correction to your drawing and sent it back to you.

-Alex
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Old Mar 06, 2011, 07:32 PM
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Hi Alex,

I've got spring break coming up in a week and some time to work on antennas. I have enough stubs to make the cloverleaf and skew planer antennas, but I want to make several dipoles and helix antennas for you to test. If I shoot you some money for shipping via paypal could I take you up on your offer to send me some cables?

Thanks,

Tom
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Old Mar 07, 2011, 06:24 AM
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Yes. I just need your address. The helix is a fickle beast. You need to be VERY precise with the match. This is why I recommend using the conductor match or the Hecker transformer.

I put a piece of 1/8" balsa under a 1/4 wave section of 1/4" tubing and it gets the SWR near perfect every time. The hecker transformer works like magic and can be way off, but it attenuates the signal a bit.

I personally use the tapered stub match, but that's because I have the testing equipment to make it perfect. The tapered match usually gets very close on a blind try. The trick is the feedpoint. You need to make the base of the tapered stub as wide as the coaxial cable (or just a bit less) and make the coaxil cable feed in perfectly flat and secured against the ground plane. This is where the matching is most critical. Get it correct and the antenna becomes the best antenna you'll ever use (until I develop the CP BiQuad ).

-Alex
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Old Mar 07, 2011, 08:02 AM
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My 2.5ghz 12 turn helix:
I decided to use the tapered strip match., coax feed is from the bottom.
Note that I still need to cut the helix to make it exactly 12 turns.
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Old Mar 07, 2011, 11:29 AM
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Nice build Hugo. What wire gauge did you use? 10 and 12AWG work best in my experiments for 2.4GHz.

Also, how are you planning on tununig that beast?

-Alex
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Old Mar 07, 2011, 11:37 AM
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Thx Alex!
It is copper tubing about the size of 12awg, but much lighter.
I'm thinking of buying a meter like yours. If not, I'll go for a diversity match against a 11db patch and see what can make it better than the patch.

-Hugo
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Old Mar 07, 2011, 11:44 AM
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If you were careful with your measurments you will be below 1.5 SWR. I have yet to make one with higher SWR on the first try. Like I said, that feedpoint is very fickle. That's why I recommend not tapering the match to a point as I was doing before.

In any case, prepare to be amazed at what that antenna will do with a skew-planar wheel or Cloverleaf on the TX.

-Alex
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Old Mar 07, 2011, 12:07 PM
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I did not made it sharp, it's a bit wider that it's height above the ground plane, rest is as acurate as my caliper.
I have both CL and SPW ready, just need some snow to melt and this FPV season's gonna rock.

What difference make a 1.5 SWR to a 1.1SWR?

-Hugo
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Old Mar 07, 2011, 12:49 PM
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Quote:
Originally Posted by Hugeone View Post
What difference make a 1.5 SWR to a 1.1SWR?

-Hugo
Very little on the RX side. TX side you get about 70% power out. On the RX side you get about 90% efficiency out. Not bad. RX impedance isn't well specified like TX impedance is.

-Alex
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Old Mar 07, 2011, 12:51 PM
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Is that 90% efficiency of the estimated efficiency of the helix (you stated the 12 turn is about 60% efficient)
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Old Mar 07, 2011, 01:06 PM
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Yes. Efficiencies are multiplied. High gain antennas typically have low efficiency. The helical is a decent antenna for the most part. It beats grid antannas which are usually 50% or less.

-Alex
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Old Mar 10, 2011, 10:00 AM
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Blue Chip's Avatar
United States, FL
Joined Oct 2005
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So is it safe to say that a 12 turn would drop to about 9.5dbi when used with the V antenna?

Even though the tx side is lineal - and the rx side is circular - does it really make that much of an improvement - even if the antennas aren't matched?

Also - anyone seeing any kind of distances (3+ miles) out of a mismatched setup yet?
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Last edited by Blue Chip; Mar 10, 2011 at 10:09 AM.
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