5.4. Slim Jim Antenna

I wanted to build a highly portable antenna which I can throw in a rucksack and carry around while using my Anytone 868 radio. The Slim Jim fits that bill perfectly. I followed the instructions from Essexham which are really excellent, so no reason to duplicate them here.

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Set in a field near by, on the 3meter poll I was able to make contacts around 10 miles away using my Anytone 868, on 145Mhz with 5watts.

5.4.1. Antenna mount

I also made a simple plastic mount which the Slim Jim hooks onto with a carabena. You can download the STL file SlimJimHook.stl. The hole in the middle is the right size to screw onto the painters poll.

5.4.2. Guy Ropes

To raise my antenna, I used a telescopic painters pole, but to keep it vertical I had to make some guy ropes. As a nice rule of thumb you want 45 degree angle between the rope and the ground.

ropelength = \frac { height } { sin(45) }

Guy rope attaching point height => Rope length = 0

This gives the minimum length for the guy rope, obviously you need to add length for tying knots and looping through the tensioner, add at least 50cms.

I bought some 3 core Paracod from Amazon. this is great stuff for the price. It holds together well, has a good strength for size size.

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5.4.2.1. Guy rope Winders

I hate tangled ropes or wires. So I made some simple plastic winders, to wrap each guy rope on. It takes 1hour to print 2 winders. I wound 5 meters on these which is plenty for my painters pole.

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You can download winder.stl to print your own.

5.4.2.2. Guy rope tensioners

Simple small bit of plastic to tension the guy rope. Each hole is 5mm in size, which is just enough for the rope to pass through, it doesn’t want to be too big as there will not be enough friction to hold it tight.

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You can download tensioner.stl to print your own.