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Old Jan 14, 2012, 10:24 AM
Always soldering
Joined Dec 2011
234 Posts
Hey guys, finally I decided to give my helical a chance and instead of building a new one, try to improve what allready have!

I add the Alex wave trap match to the antenna and I am getting better numbers.

After doing some testing I note that the wave trap its not perfectly on the center of the first 1/4 turn!

I attach some pictures and a video as well!

5.8GHz CP Helical antenna with IBcrazy wave trap match test! (1 min 12 sec)


If I do my maths well the results are :

Without the wave trap match : SWR 4.92:1

With the wave trap match : SWR 2.38:1

The Vf really improves almost at double, while the Vr is 0.20V less than the first test, great news to me!

Please guys when have a chance give it a look, your input is greatly appreciatte!!

Cheers

Martin
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Old Jan 14, 2012, 01:27 PM
The Dreamer
Pisces's Avatar
Sydney, Australia
Joined Dec 2010
911 Posts
Martin,

Super good.

I forgot yesterday to comment on your video for Vf : Vr ratio. As you have found the Vf changes as the Vr changes. The Vr changes as you tune the antenna and then the Vf gets higher VDC.

As you can see from the video yesterday the CL antenna had the highest Vf. The SPW next, rubber ducky and then the very poor out of tune helical the lowest Vf. Of course you are tuning for the lowest Vr but I'm pointing out that this also affects the Vf as your video shows.

What this means is that as you tune the antenna for minimum Vr and get as close as possible to Vr = 0 VDC the Vf gets higher VDC. So it is then necessary to repeat and measure for the forward power reference Vf again. This is as the last step before doing the calculation reverse the coupler and measure again the Vf again. Then do the calculation for the final VSWR measurement.

For the helical it is possible to get a nearly perfect match 1 : 1.

EDIT: As IBCrazy has often repeated the advice, the height of the wavetrap above the back reflector plate has the most effect on getting a good match. Maybe I think your wavetrap needs to be closer to the reflector plate. As it gets closer to the plate then the Vr should get lower VDC and give a better VSWR calculation. If this is not the case and then wavetrap is too close to the reflector plate then the opposite needs to be done. Increase the distance of the wavetrap from the reflector plate.

Your nearly there with a good helical

Lindsay
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Last edited by Pisces; Jan 14, 2012 at 03:05 PM. Reason: typos..
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Old Jan 14, 2012, 05:19 PM
Always soldering
Joined Dec 2011
234 Posts
Hey Lindsay! Nice to hear you! Thanks for the advice!
I think that now I must try and build a new helical with a thinner wire.
Itīs so dificult to bend this one and the reflector is far from flat. I made the reflector with the bottom of a Pringles can.
To do the first 1/4 turn more paralell to the reflector I must de-solder then bend then re-solder everything. Also I must use a torch to heat up the wire to solder the wave trap match cause is so thick that my 12V soldering iron is non capable to build up the necessary heat for a good solder joint.

Also I note that the coil spacing is at least 1 mm larger than the instructions.

The wave trap match is not at the center of the first 1/4 turn, its more on the last part of it.
Its all so small on this frequency that I must be very carefull on the measurements.

The total lenght of the spiral must be 48mm and mine is 52mm, so I think all this things must be improved to get a good one.

Anyway I am getting a great video signal with this antenna, no rain or noise at close range combined with the SPW on the 10mW Tx.

Alex wave trap match is working pretty well I think and is super easy to build, when I plug all for the first time after adding this I can believe that the Vf improves so much only with this.

Im running off topic maybe I must post this on the helical thread.

Cheers

Martin
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Old Jan 14, 2012, 06:35 PM
The Dreamer
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Sydney, Australia
Joined Dec 2010
911 Posts
Hi Martin,

All understood about your problem with bending and soldering that heavy gauge wire on your helical.

You obviously also know what is wrong with your helical and then what needs to be done to get the helical to be a good VSWR match.

Maybe not off off topic here as it is a good example of how to tune an antenna with the IBCrazy VSWR meter. You are the first to do this on RC Group as a DIY IBCrazy project build. ++ great videos you make.

Hope some others comment on your great work.

Lindsay
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Old Jan 15, 2012, 03:31 AM
Always soldering
Joined Dec 2011
234 Posts
Hey Lindsay thanks for the comments and I also wait for the rest of the groups to give their thoughts!!!

I found this datasheet (attachment) seems to be positive and negative different ones and I have no idea what it is but Iam reading now.

Can you give me some clue about this Lindsay?

Cheers

Martin
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Old Jan 15, 2012, 05:01 AM
The Dreamer
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Sydney, Australia
Joined Dec 2010
911 Posts
Quote:
Originally Posted by Martinba77 View Post
Hey Lindsay thanks for the comments and I also wait for the rest of the groups to give their thoughts!!!

I found this datasheet (attachment) seems to be positive and negative different ones and I have no idea what it is but Iam reading now.

Can you give me some clue about this Lindsay?

Cheers

Martin
Hi Martin,

A coaxial detector and sometimes referred to as a crystal detector is a commercial version similar in operation to the IBCrazy DIY schottky diode detector. Same beast more or less. The Agilent detector is 50 Ohms input impedance.

Usually expensive even as a used item on ebay. Good specs on the Agilent detector DC to 26GHz. It is a precision detector with a guaranteed specification.

Do you have one of these Agilent detectors? You can give it a test on your directional coupler and measure VSWR.

Lindsay
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Old Jan 15, 2012, 04:26 PM
Always soldering
Joined Dec 2011
234 Posts
Hey Lindsay no I dont have the Agilent detector and as you say before it is very expensive, founded at 180 Euros used here In Italy.
Today I redo the helical and build the first 1/4 turn parallel to the reflector hence the wave trap match near too and I get on Vr 0.34 and on Vf 1.25.
So the new SWR 1.77:1

By this time my reflector is no more flat and I must found other material to build a new one as well as the recommended 1 mm diameter copper wire.

Gone try this the coming days and wait to the attenuators to come to see if I can do some measurements and found if the detector is accurate or not.

Im start to think to move my information to the lab to share with the guys there also, after all this Alex project starts there!

Thanks and have a nice day!

Cheers

Martin
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Old Jan 15, 2012, 04:33 PM
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Joined Mar 2009
37 Posts
At the end..... now i want to build SWR meter.
But I cant understand, if the best solution is use Pisces's MOD or not...
And what is PRO with MOD bias ?


Thanks
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Old Jan 15, 2012, 06:54 PM
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Joined Jul 2004
505 Posts
Hi all. I've just built my SWR meter and tested it. I've got a question.....Is the Vr supposed to fluctuate even when not touching it and also give different readings depending on its position.
Sorry in advance for the poor quality vid, it was done using my iphone...in a rush
SWR Meter test (3 min 26 sec)

Cheers
Cadders
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Old Jan 16, 2012, 12:11 AM
The Dreamer
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Sydney, Australia
Joined Dec 2010
911 Posts
VSWR Meter- Detector 2.8VDC at 200mW 5.8GHz

Hi Group,

The pictures attached below will finish off my VSWR meter build test results. These results augment my previous test results in my post #72

As shown in my earlier build sketches the detector is built on the back of a SMA-PCB connector using SMD components and gives 2.8VDC output at 200mW 5.8GHz into a 10dB directional coupler.

Picture 3.
WARNING: NO NOT DO THIS TEST USING YOUR VTX.
HIGH VSWR MAY DAMAGE YOUR VTX

Knowledgeable Amateur and Engineer may find picture 3 interesting. Vf = Vr

Skeptic's and the like may find it a tad disappointing result.

My Eureka moment..exonerated..Im out of here.
Lindsay
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Last edited by Pisces; Mar 03, 2012 at 03:55 PM. Reason: forgot the smilie
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Old Jan 16, 2012, 04:56 AM
Always soldering
Joined Dec 2011
234 Posts
Hey Lindsay what a great job men!!! You are contributing so so much to this thread I really aprecciate all your support!!! I learn a lot from you!

And you guys also are doing a great job, it whorts just to try this build!!!Its just my modest opinion cause I dont have the knowledge but I like so much to see that we are trying this build! Hope you get great results with your measurements.

I am just thinking about now to give a try to Lindsay build as well, it is very interesting and looks so well made all his work!!!

Yes definitly i am gone try this!

BTW: Lindsay the picture 3 significate that your detector is accurate??? Please explain...Please please

cheers

Martin
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Old Jan 16, 2012, 05:03 AM
Always soldering
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Cadders your multimeter is set at 2000mV? Mine do the same thing! What if you put on 20V?

Let me know...
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Old Jan 16, 2012, 05:07 AM
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Quote:
Originally Posted by Martinba77 View Post
Cadders your multimeter is set at 2000mV? Mine do the same thing! What if you put on 20V?

Let me know...
Why you dont use Bias Mod ?


thanks
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Old Jan 16, 2012, 05:20 AM
Always soldering
Joined Dec 2011
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Hey Piopio honestly I dont know what is a BIAS before I read the Lindsay work!!
I am just new to all this. No background at all.

Now when I finish to assimilate all the info and components (pots and all other) I gone build the Lindsay BIAS off course.

Thank you!!!
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Old Jan 16, 2012, 08:35 AM
Engineer for Christ
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Amherst, VA
Joined Jun 2006
10,453 Posts
@Martin - Keep playing with that wavetrap. Bend it and just it up and down until you hit zero reflected power. The wavetrap adjusts the capacitance of the helix more than anything. If you would look at a small slice of the antenna, you'd see the wavetrap is in fact a parallel plate capacitor!

@Cadders - A few people have reported this. Make sure your coaxial cable from the coupler is not excessively long and be sure that the exposed run of cbale exiting the coaxial cable shield is less than 1/8th wavelength. You also want to be sure your system is isolated (no outside interference due to proximity changes) and your capacitor is solidly connected.

-Alex
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