Typically you want 2 to 4 PSI of pressure in the transmission line. Andrews
the company that sells Heliax and antennas sells a dehydrator that is used a
lot at broadcast transmitters. I had to purchase one a couple years back and
if I remember correctly is was in $ 800.00 price class.
Terry W6RU
----- Original Message -----
From: "Jim Lux" <jimlux@earthlink.net>
To: "Courtney Judd" <k4wi@earthlink.net>; <towertalk@contesting.com>
Sent: Wednesday, May 28, 2003 8:27 PM
Subject: Re: [TowerTalk] Feedline question
> Several approaches spring to mind, and some analysis as well..
>
> Look at your flow rate and the pressure you're using and see if you can
> bound the number of pinholes. Flow through a small orifice is something
you
> can look up in a table.
>
> Liquid nitrogen (LN2) is much cheaper than nitrogen in bottles, as long as
> the pressure you need is <235 psi. So called high-pressure dewars will
> pressurize to 200 psi, low pressure dewars go to around 20 psi.. A
standard
> GP45 (that's 45 gallons) is around 2000 cu ft of nitrogen (at STP), runs
> around $90 for a fill, and loses 1% a day (and that 1% would nicely
> pressurize your line, eh?) The gas connection on the dewar is the
standard
> CGA gas fitting for nitrogen (CGA-580?)
>
> Using dry air is another possibility, but you have to look at the
> infrastructure to dry the air adequately. W.W.Grainger and McMaster-Carr
> both have the equipment in their catalogs. Several kilobucks is my
> recollection, and you can buy a lot of dry nitrogen for that, and for zero
> capital investment. The other thing to think about is why they're using
> N2.. Are they worried about oxidation? and if so, you'll need a molecular
> sieve, which increases the operating costs. Again, it also depends on how
> dry you need it. If a dew point of 32F is good enough, then almost any
> dehumidifier will work, but if you need "real dry", the cost goes up.
>
> LN2 is probably your friend...
> $90 for 2000+ cu ft in a GP45, vs $12-20 for 300 cu ft in K bottles...In
the
> bottles, you're paying for the electricity to compress it to 3000
> psi..since the original source of the N2 is a bulk liquid truck.
>
> Another gas to consider: CO2 can be very cheap, although N2 is cheaper on
a
> cubic foot basis, usually, and CO2 combines with water to form carbonic
> acid, which is muy bad from a corrosion standpoint.
>
> Jim, W6RMK
>
>
>
> ----- Original Message -----
> From: "Courtney Judd" <k4wi@earthlink.net>
> To: <towertalk@contesting.com>
> Sent: Wednesday, May 28, 2003 6:05 PM
> Subject: [TowerTalk] Feedline question
>
>
> > I have an interesting question for the gurus out there. I have been
hired
> as
> > the remote site manager for a fm station. Basically, I just look after
the
> > site and keep the operation up and going. The question pertains to
> > pressurized Nitrogen and the feedline. This is 600 feet of 4 inch
> hard-line
> > with N tanks hooked to it supposedly to keep moisture out. This feedline
> is
> > old and has what I believe to be many pinholes thru out it. Management
> won't
> > consider replacement but is complaining about the number of bottles of
> > compressed N that I am using. What about replacing N with a small air
> pump
> > and keep the feedline pressurized with air taken from inside the
> transmitter
> > house... air conditioned and de-humidified... air is 70% N anyway! It's
> > running 18 KW out and SWR on the feedline is 1:1. Any comments or ideas?
> > Thanks Cort
> >
> > Courtney Judd K4WI / NA4W
> > 2300 County Road 61
> > Uniontown, Alabama 36786
> >
> >
> > _______________________________________________
> >
> > See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
> Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with
any
> questions and ask for Sherman, W2FLA.
> >
> > _______________________________________________
> > TowerTalk mailing list
> > TowerTalk@contesting.com
> > http://lists.contesting.com/mailman/listinfo/towertalk
>
> _______________________________________________
>
> See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless
Weather Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any
questions and ask for Sherman, W2FLA.
>
> _______________________________________________
> TowerTalk mailing list
> TowerTalk@contesting.com
> http://lists.contesting.com/mailman/listinfo/towertalk
>
|