Emergency Antenna

This antenna was built after a surprise greeting upon arriving on site to repair a low power radio telemetry system "Why have you come? I told them the antenna was stolen and have not had the time to replace it".

With this in mind we investigated the site and found, in our favour, the thieves had left behind almost all of the antenna feed cable.

Armed with this we obtained some plastic PVC piping and assembled the antenna pictured. Signal strength comparisons with a magnetic mount mobile antenna proved the design was sound, and as far as we are aware, this antenna is still in operation to this day.

The design is nothing more than a choked end-fed half wavelength antenna, the choke being at the tip of the dipole section.

The length of L is 71.25/f (f in MHz). Measure this distance from the end of the coax and cut all the way through the outer sheath and shield and remove these so that only the inner (with it's insulation) remains. At a distance L from this cut coil a further 2L length of coax up as tightly as possible to form a choke, we used the pipe as a former using insulation tape to hold it in place.