[TowerTalk] Open wire line some important points

[Bob Otto]

Hello Tom,

I'm committed to using coax (I'll get that outta the way!  <G>).  I
will have three antennas I think, a Force12 C31XR, Force12 WARC 2/2,
and a Force12 MAG 240N on top of a 88' or 96' aluminum Heights Tower.
(yes, I reduced it from the planned 112' to increase wind sail margin
for the three antennas).  I will need three runs of coax approximately
150' in length.  What coax would you all recommend as the BEST coax
for durability and least loss?  Single center wire or multistrand?
What kind of connectors? If I use a hardline, should I use multistrand
for the last 20' at the top for rotation of the antennas or do I
negate the advantage of using hardline by adding a coupling?

I will also have 2M/70CM antennas on the side of the tower at lower
heights.  What is recommended there?   The coax length would be
probably 100'-150'.

I appreciate the input -- I'm trying to get my "list of material" put
together.

73's from.......

Bob Otto
N8NGA@one.net
Cincinnati, Ohio

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Thursday, September 14, 2000, 10:21:10 AM, you wrote:


>> W1EVT, winner of the first 5BDXCC, uses 4 wire open wire
>> lines to run under the road and up the hill to his 19 towers
>> with 3 sets of stacked wire arrays (two half waves in phase
>> stacked every half wavelength) for every band.
>> Several of my dipoles are fed with ladderline and used 
>> successfully on multiple bands.  I have no problem
>> with running the ladderline across my yard suspended
>> from tree limbs and guy wires.


TR> Marconi and others used spark to set the world's distance record.

TR> I still use spark in my lawn mower and car.

TR> All things have their place, but we should remember two important 
TR> things:

TR> 1.) When the line is electrically short (less than around 1/4 wl) loss 
TR> is a function of conductor diameter and current.  Lowest loss does 
TR> not occur with lowest SWR on the line! Lowest loss occurs when 
TR> the line has a mismatch in the direction that lowers current in the 
TR> line.

TR> 2.) Ladder line, or open wire line with small conductors, has more 
TR> loss than most conventional coax when used to feed a 50 ohm load.

TR> 3.) Ladder line really gets lossy when it is wet. You might as be 
TR> using RG-58 in some cases.

TR> 4.) If the coax is matched, and the ladder line is mismatched
TR> by running it to a 50 ohm load, the losses are about the same in 
TR> dry weather between ladder line and foam insulated RG-8 style 
TR> cables.

TR> Real open wire line with large conductors is pretty good, except for 
TR> physical problems. For most matched line installations, coax will 
TR> be better.


 
TR> 73, Tom W8JI
TR> w8ji@contesting.com

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