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Old Jun 07, 2011, 03:59 PM
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Hello Alex,
I think this was not asked before and I did not find the answer, but could of missed it.
Quote:
PVC pipe former outer diameter range in inches = 3000/f in MHZ Ė to Ė 4600/f in MHz
so if I plan to use the 2450Mhz band I would need a pipe which diameter is from 3000/2450 * 25.4 ~ 31.1mm to 4600/2450 * 25.4 ~ 47.69mm
it is a difference of ~16mm in diameter, so my question would be - what diameter pipe would be best and why there is such a big error that does not matter
Thanks
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Old Jun 07, 2011, 04:04 PM
Kiwi in Germany
whakahere's Avatar
Germany
Joined Jun 2010
2,292 Posts
Quote:
Originally Posted by vipix View Post
Can you look at my new 5-turn 5,8ghz helical?
It`s good?
Mounted on receiver with magnets, next photo is my tripod GS.
very nice. I found you can strip a dipole and use that wire as it is long enough (might not be). Magnets is a great idea too. question, since the case is metal and the magnets are metal wouldn't that change the base plate for the antenna??
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Old Jun 07, 2011, 04:10 PM
FPV from Lithuania
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Lithuania
Joined Mar 2007
128 Posts
Quote:
Originally Posted by whakahere View Post
very nice. I found you can strip a dipole and use that wire as it is long enough (might not be). Magnets is a great idea too. question, since the case is metal and the magnets are metal wouldn't that change the base plate for the antenna??
I ordered two wi-fi dipoles for that reason antennas are cheaper when RP-SMA connectors in shops...

I dont know about metal case, for this Alex have answer.
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Old Jun 07, 2011, 04:27 PM
Kiwi in Germany
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Germany
Joined Jun 2010
2,292 Posts
Quote:
Originally Posted by vipix View Post
I ordered two wi-fi dipoles for that reason antennas are cheaper when RP-SMA connectors in shops...

I dont know about metal case, for this Alex have answer.
yea I have a few of these coming

http://cgi.ebay.com/12in-RP-SMA-male...#ht_2689wt_907

much cheaper than making them yourself. and a little easier!!

edit: I just when and changed my setup. No more block of foam!!! I took it off and use Velcro. Your idea on the case was great!!!
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Old Jun 08, 2011, 01:20 PM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by aSa2 View Post
Hello Alex,
I think this was not asked before and I did not find the answer, but could of missed it.

so if I plan to use the 2450Mhz band I would need a pipe which diameter is from 3000/2450 * 25.4 ~ 31.1mm to 4600/2450 * 25.4 ~ 47.69mm
it is a difference of ~16mm in diameter, so my question would be - what diameter pipe would be best and why there is such a big error that does not matter
Thanks
The helical is a very wideband antenna. Ideally you want to have a circumference equal to 1 wavelength. However anything in that range makes a good antenna. just be sure your coil spacing is ~.25*former circumference. The helical is extremely tolerant of error. You can really mess up and make a good antenna.

-Alex
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Old Jun 08, 2011, 01:22 PM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by whakahere View Post
very nice. I found you can strip a dipole and use that wire as it is long enough (might not be). Magnets is a great idea too. question, since the case is metal and the magnets are metal wouldn't that change the base plate for the antenna??
Sort of. It will cause some side lobe radiation. However the helical is circularly polarized so the sidelobes shouldn't be a multipath problem.

-Alex
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Old Jun 15, 2011, 12:31 AM
FPV Pilot
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United States, OR, Beaverton
Joined Mar 2008
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Quote:
Originally Posted by IBCrazy View Post
The community has recently seen a few FPVerís including myself gravitating toward circular polarization. Hamís have been using it for many years for ATV and satellite communications. Old Man Mike has proven the incredible benefits of using a CP system on his quad copter in its ability to reject multipath interference. I have seen its benefits in never losing my signal due to banking the plane. The problem with CP is mainly in that the antennas are generally not easy, nor well understood. It is my belief that CP is the way of the future of FPV and thus, this tutorial gives you a fairly easy to make directional CP antenna that can be mounted to an antenna tracker: the helical.

Advantages - Can be made to vitually any gain you desire. Easy to make and truly circularly polarized.

Disadvantage - Efficiency drops with added turns. Maximum efficiency is about 80% with a 3-4 turn helical and drops to about 60% at 12 turns.

The helical antenna when in axial mode is incredibly wide band which makes it great to receive our wide band analog signals as well as making it great for construction because building tolerances are incredibly loose. Thus, if you want an easy to construct antenna that will keep signal in a bank, this is the one for you. I know the impedance match section looks cumbersome. Itís not. Donít over think this one. Itís pretty easy.

I will be making two types of helicals: a former wound helical, and a cross supported helical. The former wound unit is much easier to build, but the proper size former may not be available. The cross supported helical is more efficient and can be made at any frequency, but is harder to make. It is your choice.

My helicals will be built for 1280MHz. You can scale the design to fit any frequency by the simple equation:
1280/Your frequency * My dimension = Your dimension

Or you can simply calculate it with the equations given in the second post.

For an example of a 2.4GHz helix, you can see Jason Heckerís design here: http://www.wireless.org.au/~jhecker/helix/


-Alex
IBCrazy, I must be too thick headed or something, I just can't understand how to scale this up to 5.8GHz. Is there a build thread for one of these for 5.8 GHz that shows the actual calculations ? I thought I was getting pretty good after I built and flew your CLs but I'm really having trouble getting my mind around this helical antenna.
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Old Jun 15, 2011, 10:19 AM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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Welcome to my nightmare. 5.8GHz is a challenge I have been trying to conquer with this antenna. I have found a 5/8" dowel rod wound with 14AWG wire using a hecker match works pretty well. I'm working on a stub match as well. Your coil spacing should be between 7/16" and 1/2".

I hope this helps you,

-Alex
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Old Jun 15, 2011, 12:41 PM
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Germany
Joined Jun 2010
34 Posts
Maybe this was asked before, but I didn't find the answer. Concerning the diameter and the spacing: do you measure from the middle of the wire, or is ist from outside to outside? In other words: I'm going for 5,8 GHz and I am going to use a 2 mm diameter wire. Thus, if I bend a spiral, the outer diameter will be somewhere near 19 mm whereas the inner ist about 15 mm. Same problem with the spacing. I think, this difference won't be in the range of "never mind". Hope my question is clear, else I have to sketch it up. Thx for your great work for the community, Alex!
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Old Jun 15, 2011, 01:01 PM
um.. yeah, I can make that fly
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United Kingdom, Milton Keynes
Joined Jun 2007
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I would always use the centre of the wire for both diameter and spacing.

CJ
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Old Jun 15, 2011, 02:01 PM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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Ideally you go for the center of the wire. However this antenna is really wideband, so it matters very little where you take your measurements.

-Alex
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Old Jun 15, 2011, 02:32 PM
FPV Pilot
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United States, OR, Beaverton
Joined Mar 2008
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Quote:
Originally Posted by IBCrazy View Post
Welcome to my nightmare. 5.8GHz is a challenge I have been trying to conquer with this antenna. I have found a 5/8" dowel rod wound with 14AWG wire using a hecker match works pretty well. I'm working on a stub match as well. Your coil spacing should be between 7/16" and 1/2".

I hope this helps you,

-Alex
Thanks IB, I'll give it a try. The cost is good

How many turns should I use?
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Old Jun 15, 2011, 03:22 PM
FPV Pilot
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United States, OR, Beaverton
Joined Mar 2008
371 Posts
Quote:
Originally Posted by IBCrazy View Post
Welcome to my nightmare. 5.8GHz is a challenge I have been trying to conquer with this antenna. I have found a 5/8" dowel rod wound with 14AWG wire using a hecker match works pretty well. I'm working on a stub match as well. Your coil spacing should be between 7/16" and 1/2".

I hope this helps you,

-Alex
Thanks IB, I'll give it a try. The cost is good
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Old Jun 15, 2011, 05:35 PM
Yes, "that" Karl...
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Canada, BC, Burnaby
Joined Mar 2007
1,680 Posts
Could I use 1/4" copper tubing wrapped around PVC with a microstip and see good results?

Planning on building one tonight and want to make sure I have all the parts I need. As an hvac tech, I have 1/4" tubing by the yard laying around.
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Old Jun 16, 2011, 10:44 AM
SX_
.........lost..........
Zambia, Lusaka, Lusaka
Joined Jun 2005
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Quote:
Originally Posted by karl k View Post
Could I use 1/4" copper tubing wrapped around PVC with a microstip and see good results?

Planning on building one tonight and want to make sure I have all the parts I need. As an hvac tech, I have 1/4" tubing by the yard laying around.

I would also like to know i want to make a helical for 900MHz and have (i think) 1/4" copper tube( the outside dia looks like 8-9mm and inside dia is 6mm)

Thanks
Willie
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