[TowerTalk] Collins Coaxial Balun

[geo.johnson@worldnet.att.net]

Hi Mike,
Thanks for your note.  I wish I could find my old issue!  As I recall
the design, a larger inductance (more turns) will be needed on the lower
frequencies to obtain good balun 'operation'.  This design actually does
behave as a 'bandpass' transformer.  It is a short circuit at DC.  It is
limited at the upper end by its self resonance (just like any coil). 
The dimensions are from my notes wherein I referenced the article
directly so I think it is W6TC's version which I use for my tribander.

I have used the device on a G5RV which worked fine but I would not have
confidence that I had good 'balun' transformation on 80m or 40m. 
Correspondingly, the version with more turns would probably not work
well at 10m or 15m.  I defer to W6TC's discussion which, as I remember,
noted his measurements of different designs.

In the meantime, I'll dig through my stuff and see if I can find any
more information.  Now my engineering instincts have been piqued!!

73, George W1ZT
     
nasfred@interserf.net wrote:
> 
> Hello George,
> 
> Thanks for bringing to our attention the balun - dug out the Mar. '80 issue
> of HR.
> 
> How low in freq. does your adjustments in length of the coax and wire allow
> the balun to function?
> 
> In the George Badger's, W6TC, article his is designed (used twice the wire
> lengths you used) for use on the low bands - 160 thru 40ty - with hook-up
> wire for the second winding.  Looking for a balun to use with a used TH6 I'm
> refurbishing.
> 
> Thanks again, George, for bringing up a design and solution that is timeless.
> 
>         73,
>         Mike, K4GMH
> 
> At 06:52 PM 11/18/97 -0800, you wrote:
> >RSOLOMON@systems.TEXTRON.COM wrote:
> >>
> >>      Since I am taking the 402BA down to rebuild, I might as well replace
> >>      the coax (Preventative measure). The Collins Coaxial balun interests
> >>      me. Not having a CQ library, can anyone provide more info on this.
> >>
> >>         Thanks, Dick, W1KSZ
> >>         rsolomon@systems.textron.com
> >>
> >>
> >I use the version from Mar '80 HR for a 50ohm 1:1 balun as follows:
> >
> >       RG 8X  50" long
> >       #12 insulated wire  50" long (I use the plastic covered stranded)
> >
> >       The coax and wire are COUNTER wound into a coil of 4.5" dia to make a 3
> >1/2 turn coil of each piece.  This means that the coax is wound
> >clockwise and the wire counter clockwise with it.  The #12 wire attaches
> >to the shield of the coax at one end and then attaches to the center
> >conductor of the coax at the other end.  I tape the whole thing
> >together.
> >Put a coax connector on the same end that the #12 wire attaches to the
> >shield.  The antenna (balanced load) connects at the other end to the
> >coax shield for one line and  the center conductor+#12 wire junction for
> >the other line.  A picture is better.  I hope this helps.  The artcle
> >was excellent,  I have successfully used these things since 1980 under
> >high power and SWR conditions.
> >
> >My power tests and SWR test show it flat to about 35MHz.  I check my
> >recent one with the MFJ analyzer with similar results and I also noted a
> >self resonant frequency around 47MHz.  I use it on dipoles and my Wilson
> >System 1 through 10 meters.
> >
> >Good luck..  George W1ZT

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