[TowerTalk] Help on new Tower installation planning and Feedlines

Jim Lux jimlux at earthlink.net
Fri Feb 23 00:49:01 EST 2007

At 09:11 PM 2/22/2007, Wendell Wyly - W5FL wrote:

>All wire and conduit is new. Plan to have two HF feedlines and one
>144/440 VHF feedline and 8 cond rotor cable for Hy Gain T2X Rotor and
>a 4 or more small gauge (#24) wires to control the antenna switching
>for 80,40 dipoles and 10/12/15/17 and 20 meter 2 el quad loops or
>maybe a better antenna.  Plan to use 360 foot 1 1/2 or 2 inch pvc
>conduit for the feedlines and 3/4 or 1 inch pvc conduit for the
>control lines to be buried about 12 to 18 inches.
>Budget is kinda skimpy but always wanted to use 1/2 inch hardline due
>to low loss, but don't know if it pulls through conduit ok.

Pulling a stiff 1/2" diameter feedline (3 of them?) through a 2" 
conduit is going to be a big chore.   That 3 pieces of 1/2" is going 
to be a bundle about an inch in diameter.  You might consider goign 
to a bigger conduit size.  If you want to go less expensive, consider 
using 3" or 4" ABS drain line rather than actual PVC conduit.  It is 
a lot cheaper, and it's not like you need to hold pressure in your conduit.

>  Trade
>off is LMR 400 or LMR600 or ???. The conduit run is 140 feet to a
>pull box and then 220 feet  for a total of 360 feet.

Make sure your bends are big radius sweeps.

>  1500 Watts on
>HF and 50 Watts on 144/440 VHF. Looking at using preamp or two band
>amp/preamp on tower for 144/440 vhf due to long coax run, but unsure
>what kind works well and particularly how to power it through the
>conduit run from the house.

You can run DC up the coax (lots of "bias tee" devices available), or 
just pull some zip cord in the conduit.  Put however many volts you 
need at the sending end to get enough voltage to run a regulator at 
the far end.  Or a battery float charger at the far end and a small 
lead acid battery. or a DC/DC converter "brick"...   AWG 16 will be 4 
ohms per 1000 ft (call it 4 ohms total for out and back with your 
300-400 ft run).. Say you use a surplus 48V to 12V brick, and your 
load draws 100W.. You're looking at 2-3 A on the 48V line, which is 
about a 10-12V drop.  Feed the line with 50-54V, and the 40-44 V at 
the other end will be in the range of a typical converter.

RG-213/RG-8 type coax has a AWG 13 center conductor, so for DC it's 2 
ohms/1000 ft.

>Is direct burial coax any better or worse than LMR type or hardline
>in pvc conduit?  Soil is both sandy and rocky. The site is rural and
>ups is preferred to truck shipments, so how do they ship hardline so
>it does not get damaged or it is worth fooling with for this

Is a dB or so worth it?
Look up the loss at your HF frequencies of interest and decide.

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