The J-pole antenna has been around for many years and it is a derivative of an end feed Hertz antenna, which is voltage feed, and has a low angle of radiation. The J-poles in the form that are normally used are made of tubing, either copper or aluminum or made of 300-ohm TV twin lead cables, which can be rolled up and put in a pocket. This antenna version forms a compact, low cost and lightweight adjustable antenna which has been constructed by aluminum tubing, meeting all the typical performance characteristics of the standard λ/2 and 5/8λ antenna, suitable for many types of surveillance and monitoring applications in stationary environments. This design is incredibly resistant to the anticipated rigors of the end user abuses, while providing an efficient and stable radiating device suitable for today’s receivers and transmitters up to 400W of RF output power. The antenna based on regular J-pole antenna plans consists of aluminum tubes forming two parallel telescopic elements they can be adjusted and secured using hose clamps at any appropriate length depending on the desired frequency, in addition the special constructed feeding mechanism engaged in the tuning procedure can easily slide up and down over the outer surface of both elements and then secured over them using metallic clips providing the necessary impedance and a low VSWR at each desired frequency between 26MHz to 1GHz.

The high strength plastic insulator which is located at the base of the antenna ensures stability, even in bad weather conditions and electrical isolation between the elements and the well grounded mounting support, keeping an efficient distance between them. Using an antenna tuner unit and only the highest length element, fully extracted, the antenna can be used as a monopole antenna operating the entire HF band. Certainly the efficiency of the antenna in lower frequencies (below 26MHz) cannot equal tailor-made antennas for each specific frequency, but makes up a low cost solution providing the tuning capability at each frequency within a wide frequency spectrum starting from 1.8MHz to 1GHz with just one antenna.

Nicholas J Keramidas

SW1JDQ

Some main advantages of the antenna are:

• Just one antenna which can be easily tuned at each frequency over a wide frequency spectrum.
• Can be used as λ/2 J-pole antenna or as 5/8 λ J-pole antenna or as monopole antenna
• Easily transportable due to lightweight and low volume of its elements.
• Quick and easy mounting and dismounting.
• DC grounding through a 1:1 RF coaxial transformer (BALUN) ensuring lightning protection of the antenna.
• Easily slighting feeding-point mechanism simultaneously over both elements.
• Wing screws provided for temporary installations, easily adjusting and securing at the required frequency the length of the two elements as well as the position of the feeding mechanism.
• No guy ropes needed surrounding the elements due to the high strength antenna base insulator.
• Great for portable or temporary and permanent use such emergency, military, amateur, travelling, camping, etc

TECHNICAL SPECIFICATIONS

Frequency: As 1/2λ J-pole from 26MHz to 30MHz
                   As 5/8λ J-pole from 30MHz to 1GHz
                   As monopole from 1.8MHz to 50MHz (depending on antenna tuner unit)
Bandwidth: ± .5% ~ ± 3%
VSWR: < 1.01 (adjustable through feeding mechanism)
Gain: 2 ~ 3dbi (J-pole configuration)
Impedance: 50 Ω
Polarization: vertical
Max. RF input power: 400W
Termination: N-type female connector
Base mounting: Galvanized hangers and bolts.
Elements construction: Aluminum tubing.
Base insulator construction: Polyethylene with pressurized fiberglass rod.
Length: Fully collapsed 1.1m / fully extended 8.26m
Weight: 8Kg
Operating temperature: -40° C to + 60° C

Drawing 2 illustrates the antenna operating at 1GHz

Drawing 3 illustrates the antenna configured as monopole,
using only the highest length element fully extended, connected with an automatic antenna tuner unit.