[Elecraft] Balun with a G5RV?

[Charles Greene]

At 09:35 PM 4/21/2002 -0700, Ron D' Eau Claire wrote:
> > The two coax lines in parallel are being used as a balanced feed to the
> > antenna.  Only the center conductor is being used for the feedline.  It
> > acts like any other balanced feedline with the exception that you don't
> > have as many "gotchas" as with the "real" thing.
> > 73 de John - KC4KGU
> > K2 #2490
>
>Hi, John.
>
>Maybe I misunderstood. I thought that your schematic showed the shields
>being grounded. If they are you have losses caused by leakage and dielectric
>losses between the center conductor and the shield. These losses increase as
>the SWR or the operating frequency increase.
>
>If the shields are not connected to anything at any point, you are right.
>You won't have losses in the dielectric between the center conductor and the
>shield. But you will have losses through the dielectric to anything the
>cables come in contact with.  You need to be sure that each coaxial line is
>carefully spaced and well insulated from everything around it including the
>other coaxial line.
>
>In that case I  would think that it'd be easier (and cheaper) to use a good
>air-insulated open wire line.
>
>Ron,

I used a similar arrangement on a 40 meter dipole/multi-band antenna I was 
using.  The antenna was victim to a storm, but the feed line is still here, 
I am looking it now in a bundle of three (one for another antenna) attached 
to the ceiling of my basement.  It is easy to run through the holes in the 
walls where goes from the shack to the basement to the garage to the garage 
attic through the roof, up the pole to the antenna, where twin lead would 
have been harder to run and affected by the proximity to metal objects in 
the path.  In my installation the shield was connected to ground at the 
antenna tuner.  The article describing it, in 73 magazine, claimed the 
shield reduced noise pickup.  I guess there were losses in the coax, but 
they could be placed anywhere.  Recently on the antenna reflector, a G 
station had a problem running a feed line to his multi band antenna.  I 
believe his landlord approved coax but not open wire feed line, so he ended 
up using twin RG-8X coax.  He reported it worked well.

73, Chas, W1CG