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Old Mar 24, 2011, 07:56 PM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
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Use 14 AWG for 5.8GHz. That worked for me.
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Old Mar 25, 2011, 04:35 AM
Pat K
The Netherlands
Joined Dec 2010
382 Posts
Quote:
Originally Posted by IBCrazy View Post
Use 14 AWG for 5.8GHz. That worked for me.
Thks Alex. I've made my calculations at 5.945GHZ for the tapered match and found in my case:
- width at coax connection=1.25*2.5mm=3.1mm
- width at 1/4 turn: 750/5945*25.4=3.2mm

In fact I just need a constant width. Did I make a mistake? In that case, if I use a 14awg wire (1,6mm diameter), I can flatten it with a hammer to get it 3.2mm wide. Will this work?

For the rest, I got:
- coil inner diameter: 15,4mm
- coil pitch: 11,9mm
- length: 60mm (5 turns)
- screen: 50mm diameter

That will be a very small antenna, I guess very sensitive to manufacturing tolerances. Being that small for the screen I plan to make it from soldered copper wires to make a grid with 4mm mesh size. Will it be efficient enough?
Pat
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Old Mar 25, 2011, 08:42 AM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
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I wouldn't even consider a tapered match at 5.8GHz. Use the Hecker transformer method. There is a reason I put so many matching schemes up there - to allow you to choose the best one. Yes, I exclusively use the tapered match, but that's because I have lots of RF equipment to test it.

The mesh screen will not work. Why? The matching section requires a metal plate. Your number seem correct to me.

-Alex
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Old Mar 25, 2011, 12:09 PM
Plane and multirotor's - FPV
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Moss, Norway
Joined Jun 2007
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Old Apr 01, 2011, 03:40 AM
Pat K
The Netherlands
Joined Dec 2010
382 Posts
Quote:
Originally Posted by IBCrazy View Post
I wouldn't even consider a tapered match at 5.8GHz. Use the Hecker transformer method. There is a reason I put so many matching schemes up there - to allow you to choose the best one. Yes, I exclusively use the tapered match, but that's because I have lots of RF equipment to test it.

The mesh screen will not work. Why? The matching section requires a metal plate. Your number seem correct to me.

-Alex
Hi Alex,
I've built last evening my first Helical following your instructions (with the Hecker transformer). Made a quick test at home and seems to work quite well. Having read in details all your instructions I have a couple of questions:
- does the hecker transformer distance to the metal plate matter?
- what if the metal plate is bigger (90x50mm) instead of 50x50mm for 5,8 GHz?
- as without the hecker transformer, the antenna is 100-105 Ohm, would it make sense to use a 95 Ohm coax (RG62) and to put 2 antennas soldered in parallel on the receiver?
Pat

Edit: I mean 2 identical antennas with 2 identical coax length of 95 Ohm
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Old Apr 01, 2011, 09:03 AM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
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Originally Posted by Papat View Post
Hi Alex,
I've built last evening my first Helical following your instructions (with the Hecker transformer). Made a quick test at home and seems to work quite well. Having read in details all your instructions I have a couple of questions:
- does the hecker transformer distance to the metal plate matter?
- what if the metal plate is bigger (90x50mm) instead of 50x50mm for 5,8 GHz?
- as without the hecker transformer, the antenna is 100-105 Ohm, would it make sense to use a 95 Ohm coax (RG62) and to put 2 antennas soldered in parallel on the receiver?
Pat

Edit: I mean 2 identical antennas with 2 identical coax length of 95 Ohm
I never thought of this. You are speaking of an array... that might work very well. You need to be precise in your measurment of the cable and you'll need a tuning stub where the cables join. If only this were predictable...

The beauty of the hecker transformer is that it is not sensitive to anything. You can be way off and it works. I would simply mount it as close to the reflector as you can.

The larger reflector will cause some sidelobe radiation. This may be very useful when flying close in. The sidelobes are usually small.

-Alex
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Old Apr 01, 2011, 09:13 AM
Pat K
The Netherlands
Joined Dec 2010
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Originally Posted by IBCrazy View Post
I never thought of this. You are speaking of an array... that might work very well. You need to be precise in your measurment of the cable and you'll need a tuning stub where the cables join. If only this were predictable...
Why would a tuning stub be necessary? I was thinking of a simple wire to wire soldering. Would it work?
Pat
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Old Apr 01, 2011, 12:50 PM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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Consider how a coaxial cable does an impedance transformation:

Assuming a 110 ohm load and an RG62 cable the transformation would be from 110 Ohms at every 1/2wave interval to 82 Ohms at every odd 1/4 wave interval.

Thus, your impedance is anyone's guess if you use a random length of coaxial cable. It needs to be precise. Then you still need a tuning stub to match both antennas together in the proper phase.

-Alex
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Old Apr 02, 2011, 11:17 AM
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United States, MD, Solomons
Joined Feb 2002
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Multipathing?

Alex,
Check out this video, is the interference and eventual loss of video due to mulitpathing? I want to make sure that is my problem before i get the CP antennas. Current set up is 500mw 900mhz TX w/ rubber ducky, 8dbi patch on a tracker mounted on a tripod about 5 ft off the ground. Thanks

Kyle
FPV video interference (1 min 23 sec)
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Old Apr 02, 2011, 12:30 PM
Fidler & twidler
empeabee's Avatar
Cranfield U.K.
Joined Mar 2004
4,083 Posts
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Originally Posted by gromitvt10 View Post
Alex,
Check out this video, is the interference and eventual loss of video due to mulitpathing? I want to make sure that is my problem before i get the CP antennas. Current set up is 500mw 900mhz TX w/ rubber ducky, 8dbi patch on a tracker mounted on a tripod about 5 ft off the ground. Thanks

Kyle
IMHo its QRM - or in English - Interference.
Its so solid and stable.
Multipath is all over the place with good bits, multiple shadows, loss of sync, False colo(u)rs, brightness changes, all following each other at random while flying.
Mike
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Old Apr 02, 2011, 12:47 PM
...just an earth bound misfit
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Joined Mar 2010
660 Posts
Pax River, MD

Hmmm.... somebody at the naval air station lighting you up?
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Old Apr 02, 2011, 08:23 PM
Engineer for Christ
IBCrazy's Avatar
Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by gromitvt10 View Post
Alex,
Check out this video, is the interference and eventual loss of video due to mulitpathing? I want to make sure that is my problem before i get the CP antennas. Current set up is 500mw 900mhz TX w/ rubber ducky, 8dbi patch on a tracker mounted on a tripod about 5 ft off the ground. Thanks

Kyle
http://vimeo.com/21844819
Oh yeah, that's multipathing alright. At least where you lost it was. The lines in the video were something external, maybe noise in the ground station. Look around you and see what the signal could be reflecting from. Move your ground station if necessary.

...Or you could make the switch to circular polarization.

-Alex
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Old Apr 03, 2011, 12:33 AM
Fly FPV, sleep; repeat
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Germantown, MD
Joined Mar 2006
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Quote:
Originally Posted by gromitvt10 View Post
Alex,
Check out this video, is the interference and eventual loss of video due to mulitpathing? I want to make sure that is my problem before i get the CP antennas. Current set up is 500mw 900mhz TX w/ rubber ducky, 8dbi patch on a tracker mounted on a tripod about 5 ft off the ground. Thanks
That looks VERY similar to interference I was getting at a particular flying site. Check out the screen capture below. This was due to external interference. Turns out there was a cell tower very close to where I was flying. There also were some other antennas nearby.

But to be sure, fly your EXACT setup at a different location. That will tell you if it really is external interference (which it sure looks like to me) or something with your setup.

BTW, I was flying 900MHz also. Seems to work great at most locations. But when you happen to get near external interference, it basically renders it useless.
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Old Apr 04, 2011, 12:02 PM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
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External linies are usually external interference. Also sudden blips of static constitute external sources. Video scrambling is often multipathing. It's hard to tell them apart sometimes.

Check the video in my blog. That's what multipathing looks like. look what happens when I switch to coloverleaf antennas.

-Alex
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Old Apr 04, 2011, 01:11 PM
On a holiday?
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Uppsala, Sweden
Joined Sep 2008
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What's the main pros & cons of this antenna vs the cp biquad?
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