[BC] Air-Dielectric Sections

[Glen Kippel]

Actually, you could fill the tunnels with carbon dioxide -- nothing could
breathe in that, and it's heavier than air so it won't go anywhere.

I was reminded of that when I heard about a pair of campers that decided to
fill their air mattress from a CO2 fire extinguisher.  Well, it sounded good
at the time.  But, the mattress sprung a leak, the campers settled to the
bottom of the tent and suffocated.


On 3/8/07, Rob Atkinson <ranchorobbo at hotmail.com> wrote:
>
> <<4 Inch Heliax is pretty common for buried AM TX line at 50 KW. I think
> the
> discussion you are referring to was the one where someone wanted to use 1
> 5/8" Heliax at 50 KW which is not OK.>>
>
> yes, that was the one.  I did not realize the power handling of 4 inch was
> so far above that of 3 inch.
>
>
> <<4 Inch Heliax (HJ11-50) has an average power rating of over 600 KW at AM
> frequencies and a peak power rating of over one megawatt. This is of
> course
> at moderate temperatures and low SWR.
>
> One big technical advantage that proper cable burial offers is that if
> buried deep enough it stabilizes the temperature, keeping the cable at a
> better operating point than if it is exposed to high above ground  ambient
> temperature and solar load. Also buried cables are inherently more
> electrically stable when used in directional systems.For a new plant (no
> ground system) a 10 foot trench with lots of sand to protect the cable
> works
> well for the larger air dielectric lines. The larger lines can be quite a
> challenge to pull through ducts unless they are more like tunnels and have
> manholes at strategic intervals. There are a few 50KW stations with such
> an
> arrangement. The problem is that you have also created a nice safe home
> for
> critters, unless you can pressurize it all with nitrogen which is
> unrealistic.
>
> R
> >>
> Thanks so much for taking the time write such a thorough and easy to
> understand explanation Robert.  Much appreciated.
>
> rob atkinson
>
> Rob Atkinson wrote:
>
> >  I asked because I had the impression that the 50 kw stations with ~
> 120%
> >pos. mod. used 3" rigid line because a few days ago I read here that 3 or
> >4" air heliax could not handle the full power in the event of a vswr
> change
> >and I always thought feedline runs from the tx house to the tuning house
> >were below grade whenever possible.
> >
> >rob a.
> >
> >From: "Phil Alexander" <dynotherm at earthlink.net>
> >Reply-To: Broadcasters' Mailing List <broadcast at radiolists.net>
> >To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
> >Subject: Re: [BC] Air-Dielectric Sections
> >Date: Tue, 06 Mar 2007 08:01:17 -0500
> >
> >On 6 Mar 2007 at 0:05, Rob Atkinson wrote:
> >
> > >
> > > Phil,
> > >
> > > just trying to learn something--how is rigid line
> > > normally run below grade?
> > > That is, what is it usually placed inside of?
> > >
> >
> >Usually, it is not run below grade. However, when it
> >is done properly, it would have to be placed in something
> >like a steam tunnel. Rigid typically comes in 20 ft.
> >sections and a rigid run does require maintenance. Unless
> >there are other things in the same run like steam, water,
> >telephone, utility power etc., or overriding reasons, I
> >would never consider putting rigid line underground in
> >this day and age. Today we have air dielectic Heliax
> >and that can go u/g safely in three different ways, all
> >of which have been discussed on this list in the past,
> >and mentioned in this thread to a limited extent.
> >
> >For an existing AM plant, directional boring is probably
> >the best, taking the ground system into consideration.
> >Where that is not a problem, such as a new build-out AM
> >plant, or for a horizontal FM run, I'd be inclined to give
> >the fiber duct that Mike mentioned first consideration.
> >For a new plant, there is also always the old standby of a
> >PVC liner inside clay or concrete pipe to consider, but
> >I would never consider bare PVC. That is just asking for
> >trouble, especially where the ground freezes during winter.
> >
>
> _________________________________________________________________
> Find what you need at prices you'll love. Compare products and save at
> MSN(r)
> Shopping.
>
> http://shopping.msn.com/default/shp/?ptnrid=37,ptnrdata=24102&tcode=T001MSN20A0701
>
> _______________________________________________
>
> The BROADCAST [BC] list is sponsored by SystemsStore On-Line Sales
> Cable-Connectors-Blocks-Racks-Wire Management-Test Gear-Tools and More!
> www.SystemsStore.com       Tel: 407-656-3719    Sales at SystemsStore.com
>
>