VHF SOTA Antenna – Slim Jim

Introduction

I made a couple SOTA activations and there were other stations asking for the 2 m band.
So, I carried my mobile (5/8λ Diamond) a pair of times.

I use it with the Yaesu FT-817ND to do some CW, SSB and FM QSOs , instead of using the rubber duck.

But carrying such antenna was painful and uncomfortable. 😦

So, I search for a more suitable antenna to be used in a summit.

It should be light and foldable. Some gain is also a desirable feature.

I chose the slim jim antenna.
From several sites I made one.

The SWR are better than 1,3:1 at first try. So, it’s ok!

I don’t have equipment to conclude what are the gain, fire angle, etc.

So, I test it against the 5/8 λ mobile one.

The pratical test results are overwhelming: Even at home it shows more performance than the Diamond mobile antenna.
On summits it proof to be THE antenna for SOTA!
One could always use a yagi made of tape measure. I’ve done that. But again, portability…

And, in a windy day it’s difficult to keep the elements straight!…

SLIM JIM 2 m- The construction

This simple antenna can be used inside by supporting from string, nylon cord or used outside by hanging or supported from a fishing pole, etc

Easily made from 1,6 m of 300 Ω ribbon cable (junk box…)

 

Just follow the drawings…

First : weld the copper on top and bottom and strip about 1 cm, at 10 cm from the bottom.

Second: Cut 2 cm of the wires in one side of the ribbon, at 49 cm from the bottom

Third: make a hole for antenna suspension and weld the centre and braid of the coax (almost done…)

Finish details are :

Top
Shrinkable sleeve cover the welded wires.
A hole was made in the ribbon. In this hole passes a nylon yarn which, in turn, uses a plastic hook for antenna suspension

Cut

(of one of the conductors 49 cm from the bottom)

Shrinkable sleeve prevent infiltrations and led to a mechanical reinforcement.

The mechanical reinforcement consisted of the use of tips of the plastic cable ties which were used to hold the RG-58 in the bottom of the antenna.

Bottom

Shrinkable sleeve cover the welded wires at the bottom to cover the ribbon, including the welds of the RG-58 to the ribbon.

In addition to the visible plastic clamp, there is another tying the RG-58 and tape.

In the fields

Using the antenna at SOTA ref CT/ES-004 Monte Manique

6 to 7 turns of RG-58 form an air core RF choke.

Portability is redone every time you mount the antenna… 🙂