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Dipole antenna fabrication
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nuckolls.bob(at)aeroelect
Guest

Posted: Wed Feb 29, 2012 11:46 am Post subject: Dipole antenna fabrication

Correction of typo . . .



 	  Quote: 	
		      It took 0.2 to 0.33 uV (6 to 10 dB increase)

    to make that much difference.


	




   Bob . . .

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jan_de_jong(at)casema.nl
Guest

Posted: Wed Feb 29, 2012 12:57 pm Post subject: Dipole antenna fabrication

 	  Quote: 	
		   I am glad to see others post good info. There are many Hams out there who are quite skilled in this area. Thanks Jan de Jong. I'll be building one of those for my Glastar's vertical stab.

   

I am thinking of building one of those for the Europa vertical stab as 
	


well. The V-shape adjusts the impedance to 50 Ohms and improves 

horizontal directivity . Whether it also increases bandwidth ("more 

volume" - despite using cloth hanger wire?) I don't know.

Remarks:

- the lengths mentioned in the article may a little too great for 

perfection when put inside a fiberglass structure, even when not touching

- the Pawsey stub could be tuned using a SWR meter and a dummy load 

instead of the antenna; looking for largest possible SWR over the air 

band; the transmitter used could be protected with a guaranteed load by 

50 Ohm in-out voltage divider

- after that the antenna could be tuned looking for the smallest 

possible SWR over the air band.

- if things are to be tuned anyway then the only concern in construction 

is treating both legs of the dipole the same



I may instead go for the straight dipole as follows:

http://www.europa-aircraft.com/pdfs/buildersmanuals/CBM%20-%20ANNEX%20C.pdf

with the beads replaced by a (verified if not tuned) Pawsey stub, as 

good enough.



As an added measure 2 choke baluns 1/4 wavelength apart anywhere on the 

feedline would be effective.



I also found some literally orphaned DOS programs to play with:

http://www.zerobeat.net/G4FGQ/page3.html#S301%22

SOLNOID3 shows the effect of 4 turns of 5mm wire (coax) on 45mm former 

(min. bending diameter) as a choke balun

LINELEN shows dipole performance in terms of losses, assuming a choke 

balun. Amazingly the largest effect is the type of coax where I thought 

RG58 would be good enough for my needs.



I think Bob is right - it's not all that critical. Good enough is not so 

much worse than perfection.

I should get back to my regular program now from this interesting 

diversion into radio.



Jan de Jong

* <http://www.zerobeat.net/G4FGQ/solnoid3.exe>*

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 01, 2012 10:02 am Post subject: Dipole antenna fabrication

At 02:54 PM 2/29/2012, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Jan de Jong <jan_de_jong(at)casema.nl>



 	


    Did some further study on baluns in general and the

    Pawsey stub in particular. I discovered an interesting

    article supported by bench testing on good equipment.



    I captured the article with the intent of mirroring

    it on aeroelectric.com



    I made an unhappy discovery that there were a number

    of html syntax errors in the index of articles pertaining

    to antenna issues which I've corrected. The errors

    broke links to a number of antenna features. I believe

    they're fixed and all is right with the world . . . at

    least under the heading of "Antennas, Feedlines and Connectors"



    In addition to the balun article, you'll find a compendium

    of Bob Archer articles that I uploaded to the website several

    years ago . . . and then left them dangling link-less. 



    See:



  http://tinyurl.com/857u8x8 



    In the Huggins balun article I spotted a some toe-stubbers

    like, "Velocity Factor actually varies from 0.7 to over

    1 depending . . ."  Of course, the velocity factor could

    never exceed 1.0.



    Aside from a few items that would benefit from editing,

    I found the article informative.



 

   Bob . . .    [quote][b]

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rlborger(at)mac.com
Guest

Posted: Thu Mar 01, 2012 11:40 am Post subject: Dipole antenna fabrication

Bob,



Speaking of Bob Archer and his antennas…

I was able to connect my new Red Dot analyzer into the line between my MicroAir 760 and the Bob Archer antenna I have mounted in the vertical stab of the Europa.

Here's a picture of the antenna installation:

[img]cid:B603EF70-0DC9-43CF-A07D-FB0FD0A47F79[/img]

The coax termination to antenna is as per Archer's instructions.  Crimp eyelets on to the central conductor and onto a braid made from the shield wire.  Apply some shrink tube on the braid and coax for insulation and support.  Then attach the eyelets to the antenna with nuts & lock washers over the screw posts.

Always looked pretty crude to me, but those were the instructions so I that's what I did.

Measured SWR 1:1.2  Not bad at all.



 Blue skies & tailwinds,

Bob Borger

Europa XS Tri, Rotax 914, Airmaster C/S Prop.

Little Toot Sport Biplane, Lycoming Thunderbolt AEIO-320 EXP

3705 Lynchburg Dr.

Corinth, TX  76208-5331

Cel: 817-992-1117

rlborger(at)mac.com (rlborger(at)mac.com)

 

 

On Mar 1, 2012, at 11:59 AM, Robert L. Nuckolls, III wrote:

 	  Quote: 	
		    At 02:54 PM 2/29/2012, you wrote:

  	  Quote: 	
		  --> AeroElectric-List message posted by: Jan de Jong <jan_de_jong(at)casema.nl (jan_de_jong(at)casema.nl)>



 	


    Did some further study on baluns in general and the

    Pawsey stub in particular. I discovered an interesting

    article supported by bench testing on good equipment.



    I captured the article with the intent of mirroring

    it on aeroelectric.com



    I made an unhappy discovery that there were a number

    of html syntax errors in the index of articles pertaining

    to antenna issues which I've corrected. The errors

    broke links to a number of antenna features. I believe

    they're fixed and all is right with the world . . . at

    least under the heading of "Antennas, Feedlines and Connectors"



    In addition to the balun article, you'll find a compendium

    of Bob Archer articles that I uploaded to the website several

    years ago . . . and then left them dangling link-less. 



    See:



  http://tinyurl.com/857u8x8 



    In the Huggins balun article I spotted a some toe-stubbers

    like, "Velocity Factor actually varies from 0.7 to over

    1 depending . . ."  Of course, the velocity factor could

    never exceed 1.0.



    Aside from a few items that would benefit from editing,

    I found the article informative.



 

   Bob . . .     	  Quote: 	
		  



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jan_de_jong(at)casema.nl
Guest

Posted: Thu Mar 01, 2012 12:05 pm Post subject: Dipole antenna fabrication

Thank you Bob,



1. The Morris and Bob Archer pdf's are still not available from the 

index I'm afraid but can be found using the search facility.



2. The Higgins measurements made me think that a simple VSWR meter might 

be used to tune a Pawsey stub in the presence of a dielectric other than 

air.

What bothers me is that Mr Higgins seems to measure a velocity factor of 

1.07 (322 / 300). I wonder what might account for that.



Fascinating stuff that almost makes me buy a simple antenna & complex 

impedance analyzer. But not quite (yet).



Jan de Jong

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 01, 2012 1:16 pm Post subject: Dipole antenna fabrication

At 02:00 PM 3/1/2012, you wrote:

 	  Quote: 	
		  



Thank you Bob,



1. The Morris and Bob Archer pdf's are still not available from the 

index I'm afraid but can be found using the search facility.


	


   Thanks for the heads-up. I think it's fixed now.

   Found a couple more un-linked features.

 	  Quote: 	
		  2. The Higgins measurements made me think that a simple VSWR meter 

might be used to tune a Pawsey stub in the presence of a dielectric 

other than air.


	


   Yeah . . . that's worth some tinkering time on the

   workbench. Don't have time right now but I've got

   lots of coax scraps that I can used to refine my

   own understanding.



 	  Quote: 	
		  What bothers me is that Mr Higgins seems to measure a velocity 

factor of 1.07 (322 / 300). I wonder what might account for that.


	


   I didn't catch those warts the first time I read the

   article. I was too fascinated by the test data. I'll

   but this on my list of things to read. I think there

   are links to contact him directly. I'll verify any

   'fixes' to the article with him directly.

   Bob . . .

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nuckolls.bob(at)aeroelect
Guest

Posted: Thu Mar 01, 2012 2:51 pm Post subject: Dipole antenna fabrication

 	  Quote: 	
		  

Always looked pretty crude to me, but those were the instructions so 

I that's what I did.



Measured SWR 1:1.2  Not bad at all.


	


     Not surprised. I suspect that Bob's fabrication of

     the gamma-match and associated capacitor are designed

     to tune out much of the reactance added by the bare,

     non-coaxial lead wires. The wide geometry of the

     radiating elements do doubt contributes to a wider

     performance band-width.

   Bob . . .

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