Topband: Beverage Woes

[Greg - ZL3IX]

Hi Jim,

One other effect that fools sensitive DMM's on their resistance scale, 
is the electrochemical voltage that gets developed between the ground 
rods used for Beverage antennas.  I also experienced gross 
inconsistencies when trying to check for breaks using DC resistance checks.

For the past few years I have been using a little op-amp oscillator, 
running at about 100 Hz.  I put 100 ohms in series with the opamp 
output, and apply the signal across the terminated Bev.  I then measure 
the AC mV across the Bev, and across the 100 ohm resistor, and calculate 
the AC resistance from that.

This method has proved to be ultra reliable for detecting breaks in the 
wire.

73, Greg, ZL3IX

On 2013-10-24 02:15 a.m., Jim Garland wrote:
> I have two bidirectional 720 ft beverages that use 450 ohm ladder line,
> oriented NE-SW and NW-SE. The ladder line is supported by 4x4 wood posts,
> about 7 ft above ground, spaced every 60 ft. The antenna works well, but has
> turned out to be a maintenance nightmare. My first mistake was to anchor the
> ladder line to the top of each 4x4 post using little plastic clamps (DX
> Engineering). Those lasted about a week before being pulled apart by the
> wind. I replaced them with wood pressure plates screwed down over the ladder
> line with 2" lag screws into the top of the posts. Those lasted about a year
> before cracking and splitting. The ladder line turned out to be very
> fragile. The plastic material gets brittle and cracks, and the wind causes
> metal fatigue and eventual failure of the strands.
>
>   
>
> I've spent the past three afternoons patching up the beverages for the
> winter DX season and am only about half done.Yesterday, I thought I had
> everything fixed and only needed to phase the ladder line properly. I left
> one wire open and grounded the other wire at one end, and then used a DMM to
> identify the grounded wire. To my dismay I found an open circuit on both
> wires. A spent a couple of hours with a toner trying to find the break, but
> to no avail. Then, it occurred to me that my Fluke 87-V DMM may be giving me
> erroneous readings. I replaced the Fluke with my trusty Simpson 260 and
> discovered the wire was actually intact. Evidently, the Fluke's sensitive
> solid state ohmmeter circuit had been overloaded by the
> inductance/capacitance of the ladderline or possibly RF pickup. I should
> have known better from the get-go.
>
>   
>
> So now, I've got one of my beverages working and will start repairs on the
> 2nd one. I've decided ladder line is a terrible choice for a beverage
> antenna, at least in New Mexico, where there is intense UV sunlight and
> windy Springtimes.  My plan is to replace the ladder line with parallel
> strands of 12 AWG copperweld wire, with pass-through insulators on each 4x4
> post, and the wire anchored at each end. I'll use turnbuckles to adjust the
> tension. I'm really tired of repairing the damn antennas, and my feet hurt
> from hiking back and forth to each end.
>
> 73,
>
> Jim W8ZR
>
> _________________
> Topband Reflector
>
>