[TenTec] openwire feed OT

[Carl Moreschi]

Rick is correct about this.  If you make open wire line out of coax and
ground the shields, you have twice the loss of running a single coax line.
If you want to make open wire line out of coax, then the only practical to
way to do it is to use the coax shields as the conductors and not use the
center conductor at all.  Remember, open wire line develops its shielding by
equal and opposite currents in each side.  The resulting fields from these
conductors cancel and cause no radiation.  Using the center conductors of
coax for this ruins the opposite field cancellation and introduces all the
loss that coax has for each side.

Carl Moreschi N4PY
121 Little Bell Drive
Bell Mountain
Hays, NC 28635
----- Original Message ----- 
From: "NJ0IP" <Rick at DJ0IP.de>
To: "'Discussion of Ten-Tec Equipment'" <tentec at contesting.com>
Sent: Thursday, February 02, 2006 12:20 PM
Subject: Re: [TenTec] openwire feed OT


> Guys, this may be a stupid question, but if you use two parallel pieces of
> (long) coax, wouldn't you have twice the loss.  On the other hand,
resistors
> in parallel would mean half the loss.  In any case, coax is lossy, heavy,
> and expensive, so why would you use a long run of two coax cables?
>
> Using short lengths to going through the wall is a good idea, but then why
> would you need to tie the shields together at all and why ground them?
>
> Sinisa?
>
> Cheers,
> Rick
>
> -----Original Message-----
> From: tentec-bounces at contesting.com [mailto:tentec-bounces at contesting.com]
> On Behalf Of Darwin, Keith
> Sent: Thursday, February 02, 2006 9:05 AM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] openwire feed OT
>
> Ken (and others)
>
> Oh, man, true confession time here :-).  I've only done what I described
> one time, years ago.  I built a coax parallel feed line for a loop
> antenna.  The coax went from the back of the tuner, through the window
> and all the way to the antenna.  I connected the shields together at the
> tuner end of the line and tied it to tuner ground.  It worked fine.  I
> figured the same technique would be great for constructing a parallel
> balanced line for use inside and near things that would upset the field.
> Truth is I'm still not sure what to do with the shields :-)
>
> I believe that the 2 pieces of coax can go their separate ways as long
> as they start together and end together.  The shield isolates the center
> conductor preventing it from being affected by nearby stuff including
> the other half of the parallel feed line.
>
> I got the idea from an article in QST but don't really have the
> engineering or physics data to truly explain how it all works.
>
> In my personal case I feed RG-8x coax from the rig to the tuner which is
> mounted 50 feet away.  From the tuner I run RG-213 coax 30 feet to the
> base of my 28' vert antenna.  Doesn't work well on 80 but seems to work
> well on 40, 30, 20, 17 & 15.
>
> - Keith KD1E -
>
> -----Original Message-----
> From: tentec-bounces at contesting.com
> [mailto:tentec-bounces at contesting.com] On Behalf Of K. Indart
> Sent: Thursday, February 02, 2006 11:31 AM
> To: Discussion of Ten-Tec Equipment
> Subject: Re: [TenTec] openwire feed OT
>
> Keith,
>    I have two questions:  Do you keep the two coax pieces separated by
> the same spacing as your feed line,...or can you make ONE hole in the
> wall/window and feed both coax through one hole ?
>
>    Does it matter which end of the shields get tied together; inside the
> wall or outside the wall ?
>
>    Do you make the lengths of the coax JUST long enough to protrude
> outside and inside of the wall or how long ?
>
> Thanks, and it sounds like a very good idea.
>
> 73, Ken  WA4RPH
>
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