Introduction
I am developing an antenna system for a stratospheric balloon for the Silesian Aerospace Technology scientific club. Currently, I am creating a miniature copy of the antenna deployment system based on the mechanism used in ORCASat. The principle of operation of the mechanism is very simple: a measuring tape rolled several times into a loop unwinds spontaneously after opening the door and within a fraction of a second an antenna arm is created.
This uncommon use of measurement tape inspired me to create a portable J Pole antenna that fits in a backpack. I had a two-meter measuring tape at hand, so I decided to create an antenna for the 144MHz band.
Implementation
To calculate the dimensions of the antenna, I used a calculator from this website. I chose a 0.93 velocity factor and after minimal tuning, I got the resonance for the desired frequency.
About 10 cm of tape measure remains on the roll, which allows you to tune the antenna by shortening or lengthening it.
I marked the calculated length of the 3/4 wave element with a line and from this point you should start tuning the antenna in the field.
The tape itself can be processed easily - it can be bent with miniature pliers, drilled with metal drills, and cut with scissors.
As supports for the tape, I used PVC spacers.
The antenna can be hung on the tree by measurement tape’s rubber loop.
Problems
The measuring tape is made of sheet steel, which is poorly soldered. Nevertheless, in my opinion, it is worth covering it with a thin layer of tin in the place where the cable terminal is screwed. This can be done with a high-power soldering iron using soldering acid.
The disadvantages include the low stiffness of the antenna (SWR can change with higher wind). In addition, the measuring tape is quite fragile - it can break after being bent several times.
Ending word
Nevertheless, the antenna made in this way is an interesting experiment and I think it’s worth doing for fun. Time will tell how durable this solution is.