Circularly Polarized Helical antenna 7.5 -13 dbi - New: Wave Trap match! - Page 52 - RC Groups
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Apr 16, 2012, 09:43 PM
Engineer for Christ
IBCrazy's Avatar
Originally Posted by arashi
I am going to put my Helix on a tall mast. Details of using a loop for a reflector would be appreciated. It should lower the wind loading significantly.

Use a mesh screen for a reflector. Mind you that the wavetrap will be much closer to the screen than it would a solid reflector.

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Apr 16, 2012, 10:04 PM
Rotary~myPast,Present &Future!

Tuning Helical without an SWR Meter

Originally Posted by Matt.
Hi Guys,

Here is a few pics at my first attempt at a helical.
Please comment if you see any big mistakes.
I am now looking to try and build a SWR meter etc so I can tune this

Hi Matt, since you don't have a SWR meter now, you can use this method I'm using to tune your helical
1. Do a range test by moving the helical further and further from the VTX, point the helical at your VTX as you verify the video
2. Keep walking until you reach the point where the video starts to fade out and you notice you have a very narrow beam left
3. At this point, if you aim off slightly, the video should disappear and when you aim back at that precise angle, the video starts to recover slowly. And there would be noise (white specks) in the recovered video
4. Note how much noise there is and how long the video takes to recover
5. Now adjust the bend of the wire, right after the 1st-quarter turn. The first quarter turn should remain parallel to the reflector and so does your wave trap.
6. Reducing or increasing that upward bend will have an effect on the amount of noise in the video. If you get the correct angle, the recovery time of the video from fade-out also reduces

After this tuning, you would see a significant improvement in performance.
For example, at some corners of your house where you used to get a grainy video, you will notice that the video would appear less grainy now.
Apr 17, 2012, 03:17 PM
Always soldering

Helical first ground test...24dB attenuation.

Hi guys!

Finally I manage to do some ground test on my helical build. Details of this build are posted earlier in the thread. Post #754.

Please note this test is with in-line 24dB attenuator. VTx is 200mW.

This is aprox. 1/16 of the range.

3 turns helical and pinwheel.
Helical is 1.5 meters above ground on trypod and my test platform is at my head level wich is aprox. 1.76 meters or so.

Note that at some point I get LOS interrumpted by an old machinery laying on the field and this can be clearly see in video signal drop for a couple of seconds.

I cannot go further cause it is not allowed to enter the next field and Im allready on the cross border. Read video description + info.

Sorry video is no edit.

5.8GHz DIY 3T Helical - PW (24dB attenuation) (4 min 19 sec)

Last edited by Martinba77; Apr 17, 2012 at 03:39 PM.
Apr 18, 2012, 06:02 PM
The Dreamer
Pisces's Avatar
Originally Posted by Martinba77
Hi guys!

Finally I manage to do some ground test on my helical build. Details of this build are posted earlier in the thread. Post #754.

Please note this test is with in-line 24dB attenuator. VTx is 200mW.

This is approx. 1/16 of the range.

Excellent work. Your video was still a good strong signal at 250m. Then without the 24dB attenuator used for the range test set-up means you have tested the equivalent of 4km. Still with good strong video. CP is also working well when you rotate the pinwheel 90 degrees.

Can you post a close up photo of your ground station on the tripod with the helical. This would be interesting to see. It is not easy to see the detail in your video. Maybe also a close up photo of that hand held test bed you are using.
Apr 18, 2012, 09:47 PM
Registered User

Thanks for the tip.

Apr 18, 2012, 10:55 PM
Rotary~myPast,Present &Future!
Congrats Martin, did you tune your helical by using your DIY SWR meter? Since in theory is 4km, even dividing that by half gives you 2km, which is still good. Looking forward to see what your getting in 'practical'.
Apr 19, 2012, 12:56 AM
Registered User

DYI Direction coupler

I have been having real troubles trying to finding the appropriate coupler that's anywhere near Australia. I contacted Mictronics about his but unfortunately he is out. So I asked him to share the dimensions of the couplers he was making so I could have a go a making one myself. I have access to a cnc mill so it was fairly easy once I had the dimensions. I have attached a picture to show my first attempt.
I have ordered the diode from RS Components so now all I need to complete the SWR is a dummy load.
Is there anyway you can make one of these or is there a substitute that can be made from readily available parts?

Apr 19, 2012, 04:25 AM
The Dreamer
Pisces's Avatar
Originally Posted by terencechan
Congrats Martin, did you tune your helical by using your DIY SWR meter? Since in theory is 4km, even dividing that by half gives you 2km, which is still good. Looking forward to see what your getting in 'practical'.
Yeah, I thought it a pretty good result.
I forgot to mention I calculate the Vtx RF power into the PW antenna with 24dB attenuator.
Vtx 200mW is +23dBm then - att 24dB = -1dBm.
Then is 0.8mW RF power into the PW.
250m LOS for 0.8mW is a pretty good result I think.
Maybe Martinba77 can post a picture of the PW with the attenuator 24dB.
Apr 19, 2012, 07:25 AM
Always soldering
Glad you liked my tests guys!

The 3T Helical build details are on post #754.

I attach here pictures for attenuators and the Pinwheel antenna.

Also some GS photos, pretty simple and im working now in a more decent wiring but work just fine as it is.

The wooden platform photo is archive since I have now bare wooden stick only, I take apart all components when Im not using that. It is all velcroed to the sticks, easy to set up and change stuff placement.But with the photo you can make an idea on how it looks and works.

@Terencechan :
Yes I do tune my helical on my SWR meter. Im using the Alex wave trap match to do so. I think what you mean with "practical" is a "in flight" test, but Im not searching medium range. I want to do only short range maybe 1 to 1.5 KM im happy just with that and good video link.So this test must wait for a long long time, Im just a noob here. But since "in flight" the Fresnel zone can be a little less interrupted, I hope that the results goes even better. Remember this is 3 turns helical nothing more nothing less...this is just a ground test and the A/V Rx and A/V Tx are pretty close to the ground.

The helical is my build, the Pinwheel it is not my build.

The test is performed on CH5 5885MHz on Foxtech A/V Tx 200mW.

So for the photos now, hope you guys like it...again see post #754 + info.

I wish to thanks Alex again for his great work and support to our community.
The wave trap match is great and simple to work with...great idea for newbies like me to get a good impedance match in a simple way and without having to find difficult to get materials. Thanks Alex keep coming your great work please.
Hard work you do to improve the hobby...lots of time you put on this for free!!!

Big thank you!

#The the Ground Station box is from my Hoiki analog meter that I use to build the VSWR meter. Someone put this on garbage and I was at the right place at the right moment!


Last edited by Martinba77; Apr 19, 2012 at 07:54 AM. Reason: Checking typo...
Apr 20, 2012, 08:33 PM
steve's Avatar
OK I see you said that already I will use copper and 10mm wire and 20mm PVC tube for former. .5" turns and my reflector is 2" sq. I will go with 4 turns. Hoping to get at least a 3km range in non polluted in environment with antenna tracker. I have a 3 lobe cloverleaf on the transmitter and 4 lobe skew planar wheel on the second channel of my receiver. I'm using 600mW immersion vTx.

Does that all sound ok?
Last edited by; Apr 20, 2012 at 09:00 PM.
Apr 21, 2012, 08:45 AM
Engineer for Christ
IBCrazy's Avatar
Sounds good to me.

Apr 23, 2012, 11:39 AM
New RC geek!
HI guys.

I am currntly trying to make a helical antenna. and I got a stainless steel plate as a Reflector will that work? anyone tried that?

Inge Nikolai
Apr 23, 2012, 01:39 PM
Lame-As The real alternative!
narcas's Avatar
It will be impossible to solder onto I think
Apr 24, 2012, 09:27 AM
Registered User
Zen09's Avatar
It is possible to use steel but you need powerful flux to solder on. As for stainless steel, narcas is right, forget it.
Apr 24, 2012, 10:19 AM
New RC geek!
Thanks guys.

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