Topband: Supporting Ladder line
jeremy at maris.plus.com
Sun Jan 7 05:28:00 EST 2018
I’ve done something similar to Jim with two paralleled runs of WD1A for a bi-directional Beverage and it worked very well.
According to the specifications, WD1A is made up of two 0.85mm diameter conductors separated by 0.85mm between the inner surface of the conductors.
I took the effective diameter of two paralleled strands of WD1A to be 2mm. Two lines spaced apart by 50mm gives about 450 ohms impedance.
Paralleled strands of WD1A at 450/600 ohms are OK for RX but you want to use the line for feeding QRO to a transmit antenna, so loss matters.
I’ve considered using RG6U spaced apart by 150mm for 450 ohm TX transmission line but think that I’d need too many poles to support it with acceptable sag.
Aluminium wire or copperweld would be much better - it would be lighter and hold more tension so less sag, fewer supports needed and more consistent impedance.
Re horizontal versus vertical spacing, don’t think it will make much difference on taught lines raised above head height.
73 Jeremy G3XDK / G4AQG
> On 6 Jan 2018, at 21:05, Vic <g4byg at lindgren1.karoo.co.uk> wrote:
> Thanks for that Jim,
> Well we plan on using some on site "Shot Gun" coax (about 8 gauge diam) as the ladder line conductors with a 6 inch spacing. Which on a test length gave us around the 450 ohm impedance we require.
> I dont know the diameter of that WD1a wire but suspect it is quite small which would make home made 450 ohm line spacing very small indeed.
> Your method of supporting using the wood clamps sounds a good idea as we were concerned about the plastic clamps breaking due to flexing and UV deterioration.
> If our conductors fail through the flexing then we may bite the bullet and buy some Aluminium wire as Rik N6RK uses.
> All useful info though and thanks again Jim.
> On 06-Jan-18 20:38, Jim Garland wrote:
>> Vic, I've had nothing but bad luck in trying to support long horizontal lengths of ladder line. In my case, I have two 720 ft bidirectional beverages, which I initially made of heavy duty commercial ladder line. I supported the line with wood 4"x4" posts, spaced sixty feet apart, using the little plastic ladder line clamps, sold in the US by DX Engineering.
>> After only a month or so, the plastic clamps broke apart because of the repetitive flexing of the ladder line in breezes. I replaced the clamps with wood clamps, screwed into the top of the posts. These survived with no problem, but the ladder didn't. After six months or so, I started having breaks in the line from the flexing, and after spending two years repeatedly repairing the line, I gave up and threw away all 1500 feet of the stuff.
>> Finally, I settled on WD1a military surplus field telephone wire, available from many sources for about $50 USD in half mile lengths. I use two parallel lengths of the wire, threaded through twin ceramic insulators screwed into each 4x4 wood support (available from a farm supply store), with a pulley at the far end to equalize tension in the two lengths. In three years, it has worked perfectly, with no problems at all.
>> I'm not disparaging ladder line (or the plastic clamps) at all. The commercial stuff just isn't designed for long horizontal lengths.
>> Jim W8ZR
>>> -----Original Message-----
>>> From: Topband [mailto:topband-bounces at contesting.com] On Behalf Of Vic
>>> Sent: Saturday, January 06, 2018 01:17 PM
>>> To: topband at contesting.com
>>> Subject: Topband: Supporting Ladder line
>>> Has anyone idea's of how to support a long (750 ft) length of home made
>>> 450 ohm ladder line ?
>>> Is it possible to use it supported from posts in a vertical orientation or will that introduce
>>> I would prefer not to have it supported horizontally due to added cross arms being
>>> Have scoured internet sources but their appears little information available on the subject.
>>> I plan to feed a Marconi Tee Vertical (Hairpin Matching) with 9:1 transformers at each end
>>> of the ladder line enabling use of 50 ohm coax at each end for convenience.
>>> G4BYG (G6M)
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