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Old Feb 27, 2012, 02:32 PM
Happy Days
mudlark's Avatar
United Kingdom, England, Exmouth
Joined Mar 2001
4,184 Posts
Guys.
Can you make a helical TX antenna for ground link of say half a mile. from a barn to a farm house?
My fiance runs a farm in Washington and wants me to fit a "Lamb Cam" for the lambing season. Looking to be using a 900mhz TX RX set 800mw.
Will probably work with standard antennas but would prefer to beef it up.
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Old Feb 27, 2012, 04:45 PM
um.. yeah, I can make that fly
Carlos230023's Avatar
United Kingdom, Milton Keynes
Joined Jun 2007
3,735 Posts
Sure thing mudders,I've ground tested my 5.8ghz gear for 1km (cloverleaf to helical) though a built up area, had a quality signal. I suspect helical to helical would be good for your needs, tbh 900 MHz @ 800 mw may well be massive overkill, I reckon you'd get about 3 miles at ground level no sweat (after that you'd have to lift them off the deck to account for the earths curvature or any topography that's in the way).

CJ
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Old Feb 28, 2012, 07:14 AM
Happy Days
mudlark's Avatar
United Kingdom, England, Exmouth
Joined Mar 2001
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Cheers CJ
Just looking at over kill.
As I will only be there for two weeks I will not have time to order stuff in time. Will need to to bring every thing I need with me so just making sure.
I think I will just use the standard antennas and cross my fingers.
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Old Feb 28, 2012, 08:04 AM
I think it'll work this time!!
Chairwolf's Avatar
399 feet above Roanoke, VA
Joined Jan 2007
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Quote:
Originally Posted by TurboCinqy View Post
It's probably calculated with GPS.

It's the value above the Home Arrow.

http://youtu.be/NpX7pQNxb2Q

"You (home location) are the center of this circle"
Thanks for the reply. So if I understand correctly, your OSD is simply showing the planes' heading? And since you are, for example, flying out on a heading of 90 degrees, your return home would be on a heading of 270 (theoretically, anyway), correct?

Bob
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Old Feb 28, 2012, 08:33 AM
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Tiel, The Netherlands
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No,

After we noticed we thought the same thing.

As i said your home location is the center of the circle around you.

So 90 degrees in front of you is always 90. untill you fly over your home location.
At that point it will turn into 270 degrees.

So your 90 degrees flightline wil maintain the same value if you will fly home.

In this vid We fly on the same path most of the time.

FPV Wing with 5.8Ghz Helical. (6 min 18 sec)


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Last edited by TurboCinqy; Feb 28, 2012 at 08:43 AM.
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Old Feb 28, 2012, 09:10 AM
I think it'll work this time!!
Chairwolf's Avatar
399 feet above Roanoke, VA
Joined Jan 2007
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Quote:
Originally Posted by TurboCinqy View Post
No,

After we noticed we thought the same thing.

As i said your home location is the center of the circle around you.

So 90 degrees in front of you is always 90. untill you fly over your home location.
At that point it will turn into 270 degrees.

So your 90 degrees flightline wil maintain the same value if you will fly home.

In this vid We fly on the same path most of the time.

http://www.youtube.com/watch?v=ipRfbqwudgo
Ok, the light just came on! It's the plane's POSITION relative to you, regardless of it's direction. I understand. So 90 is 90 relative to me, no matter which way the plane is travelling. Got it.

Last question, and sorry for going off topic, but can you tell me the setting in the Remzibi software that puts this on-screen? Is it actually called "Flightline angle from home?" As I said, I'm new to the Remzibi.

Thanks so much for your patience! I appreciate it.

Bob
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Old Feb 28, 2012, 11:17 AM
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Tiel, The Netherlands
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AZIMUTH - Angle from Base Station
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Old Feb 28, 2012, 02:05 PM
I think it'll work this time!!
Chairwolf's Avatar
399 feet above Roanoke, VA
Joined Jan 2007
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Quote:
Originally Posted by TurboCinqy View Post
AZIMUTH - Angle from Base Station
Perfect! I understand now, and can see what it's doing in your video. And I see it in the software too.

Thank you!

Bob
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Old Mar 04, 2012, 04:17 AM
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Joined Sep 2011
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RHCP Helical Antenna

Hey Guys

I've been busy over the weekend. I'd be interested in your thoughts. I have not used a match.

Cheers

WN
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Old Mar 04, 2012, 07:31 AM
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Switzerland, LU, Buchrain
Joined Aug 2006
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Quote:
Originally Posted by WhiteNite1971 View Post
Hey Guys

I've been busy over the weekend. I'd be interested in your thoughts. I have not used a match.

Cheers

WN
There's not much we can say really. Unfortunately it's very very hard to predict the resonance of a helical built like this. What made me wonder is the ground plate which makes the impression like it's splitted into four quarters? Or is this just the colour of some stick you used to find the center?

At 5.8Ghz helicals are fairly difficult to tune, even when useing the wave trap aproach. Assuming you have no way to measure the resonance, all that you can try is to add a wave trap to the first quarter and try. You used pretty thick wire which makes it wideband, so chances are it will work a bit. Considder adding the wave trap, that's a little copper piece, 1/8 times 1/16 the wavelenght, so for 5.8Ghz, aproximately 3.2 x 6.5mm in size.

Markus
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Old Mar 04, 2012, 01:36 PM
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Hi Markus

The reflector is made from a printed circuit board 50mm x 50mm. I marked it using a pencil to find the centre for the cross. The wire is 1/16th inch copper tubing which was the closest match I could get to 14 AWG. I will add the wave trap in the next couple of days. Thanks for the feedback.

Regards

WN
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Old Mar 05, 2012, 06:39 AM
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Switzerland, LU, Buchrain
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Quote:
Originally Posted by WhiteNite1971 View Post
Hi Markus

The reflector is made from a printed circuit board 50mm x 50mm. I marked it using a pencil to find the centre for the cross. The wire is 1/16th inch copper tubing which was the closest match I could get to 14 AWG. I will add the wave trap in the next couple of days. Thanks for the feedback.

Regards

WN
Considering that you can't measure, having thicker wire is better. A more wideband antenna means better if you don't hit the frequency you operate your tx and rx on. It also means less efficiency and your rx will get stuffed by other nearby hf sources, but this is all a compromise obviousely. The wavetrap at least will raise the possibility that your antenna is at least in the area of where you want it.

Markus
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Old Mar 05, 2012, 01:21 PM
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Amherst, VA
Joined Jun 2006
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Quote:
Originally Posted by WhiteNite1971 View Post
Hey Guys

I've been busy over the weekend. I'd be interested in your thoughts. I have not used a match.

Cheers

WN
Make sure your feedpoint is VERY close to the reflector. Then move the first 1/4 close to the reflector to make a conductor match. Generally speaking this works well for a helical antenna at 5.8GHz even without measuring equipment.

-Alex
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Old Mar 05, 2012, 03:19 PM
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Brasil, RJ, Rio de Janeiro
Joined Aug 2011
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Hi guys, i bought from alex some time ago the helical 7,5 dbi and the closerleaf for my 1,2Ghz system. The image quality over the land was perfect, my friends became shock !! But when try to fly over the water, i have some lines on horizontal, even on short range ( 500 meters) that i dont have with my patch. This some problem with circular polarization and water?

Ps: i rx/tx are lawmate
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Old Mar 06, 2012, 02:06 AM
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Joined Mar 2012
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Newbie question regarding 5.8 GHz and wavelength

Hi there,

I am currently using the CL SPW combo of IBCrazy and I am loving it. Thank you so much Alex for everything you've done to FPV in the past years. You rock man!!

Now I am about to build a Helical Antenna as a match on my diversity receiver.

I am using the 5.8 GHz band and made myself an excel sheet to do the calculations, when I stumbled over the wave length everyone is using when building a 5.8 GHz antenna. Everyone is using 0.21 which seems correct for 2.4 GHz but (might be a silly question) isn't

Lamda = 300 / f in MHz

That would leave me with a wave length of 0.05 for a 5800 MHz wave.

That again would lead to a coil spacing of 2.5 mm... using a 1 mm wire this would lead to a 0.5 mm gab betwean the wires.

Also this seams to raise the gain of the antenna and thus narrow the beam, but according to http://jcoppens.com/ant/helix/calc.en.php

e.g. a 6 turn helical would be

95 degree beam at 0.05 wavelength
instead of 55 degree at 0.21 wavelenght


could someone lead me into the right direction?

Am I totally wrong here or am I overthinking this due to the tolerance of the 5800 MHz helical?

Thank you in advance

A.
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