Very high efficiency J-Pole vertical antenna, excellent for DX activity and local traffic.
The SmarTech 27VJ is a vertical polarization antenna, completely redesigned and optimized for maximum electrical and mechanical performance. The constructive simplicity of the J-Pole antennas does not guarantee as much certainty as to obtain maximum efficiency due to the complexity and criticality of the parts constituting the antenna.
From the electrical point of view, the antenna consists of an upper radiating part (where the maximum currents are located at about 5 m from the basis) and of a lower part that provides to feed the antenna by a rigid two-wire shorted transmission line. Here, impedance is matched to 50 ohm for coaxial cable use.
The combinations among the main and secondary stylus lengths, the distance between the two elements and the position of the sliding feed bridge, are extremely important and determine a considerable difference for the system efficiency, even though they all reach an SWR of 1.0:1
The SmarTech 27VJ was therefore designed to obtain the best configuration, thanks to the best numerical modeling algorithms, such as the PSO (Particle Swarm Optimization), and the model-measure iterative cycle used during the SmarTech prototyping phase.
From the physical point of view, the asymmetric geometry of the antenna induces particularly insidious mechanical tensions at the height of the jointed parts (above all basements), which undergo simultaneous stresses of bending and torsion. The use of very high quality materials is therefore equally important both for resistance to mechanical stress (design wind 150 km / h), and for avoiding the effects of passive resistances, which strongly degrade the whole system performance.
ABSENCE OF RADIALS
- The antenna electrical configuration does not require the use of radial elements. It can therefore also be installed in very small spaces or in building common spaces (eg roofs, terraces) where it is not allowed to occupy common spaces.
- All the antennas that require the presence of radial elements have, by definition, an efficiency proportional to the number of installed radials. The 27VJ is completely free from the efficiency degradation due to the presence of radials.
NOT AFFECTED BY HEIGHT ABOVE THE GROUND
- The antenna can be installed even at 1 m from the ground without performance decay. The point of maximum current (i.e. maximum radiation) is in fact at 5 m from the base of the antenna.
- Excellent also for mobile/portable use as it does not require necessarily high poles. Can be mounted in 3 minutes.
- The variation of the height from the ground affects only a different presence and take-off angles of secondary lobes, as shown in the analysis graphs.
LOW TAKE-OFF RADIATION ANGLES
- The key feature of the 27VJ SmarTech is an extremely low take-off angle of its main radiation lobe. In fact, whatever the installation height, the antenna keeps low over the horizon its take-off angle, as can be seen on the radiation patterns attached.
- For DX activity, low take-off angles maximize antenna performance especially on very long distance paths, where signals are the weakest of all.
- For local traffic, the low lobe prevents your power from being "wasted" upwards, optimizing the gain (in RX and TX) especially for ground signals, coming from mobile and from fixed positions.
The main structure is made of aluminum alloy EN AW-6060/82 UNI 9006/1 (Anticorodal 60/100), which provides excellent long-term durability against the most severe weather (ice, water, UV rays, fine particles, acid rain), and better resistance to heavy wind load.
The antenna is supplied with stainless steel parts AISI 304 (Inox Austenitic UNI / EN 10088) and steel S235JR2 (UNI 100 series), certified according to 2000/53 / CE + RoHs standards.
Element Insulators are made of Polypropylene PPC 5660, resistant to remarkable thermic excursions (certified for temperatures from -20°C to +130°C), with high load at break (ultimate tensile strength 25Mpa), excellent abrasion-resistant and volume resistivity > 1018
The antenna is provided with a special grease pack for joints protection
Feeding connection: SO-239
The antenna is made to obtain the maximum electrical efficiency, the best mechanical resistance and durability, thanks to its high quality materials. It is also suitable for installation in mountain areas and coastal (corrosive) areas.
SmarTech antennas are designed with the minimum necessary electrical/mechanical joints. So, parasitic resistances are the lowest possible so as to minimize unwanted RF dissipations.
In order to maintain its best performances, each antenna is individually checked before shipment.
The J-Pole antenna, more properly called J antenna, takes its name from the similar appearance to the letter J. Patented in 1909 by dr. Hans Beggerow, was used aboard Zeppelin airships since the early 1900s.
It is often produced (or home made) in configurations different from the original pure model, due to mechanical-constructive advantages which however present significant electrical and performance problems.
1. ANTENNA NOT INSULATED BY THE SUPPORT POLE
The base of the antenna, represented by the short bridge of the two-wire matching line, is often electrically connected to the support pole. Since in this point the currents are not zero, any conductive element foreign to the antenna is ran over by radio frequency, becoming an integral part of the system..
This means that the pole radiates itself causing distortions, even considerable, to the antenna radiation solid. Depending on the pole/tower length, the antenna behaviour is always different and never predictable. However, manual calibration for SWR 1.0:1 does not produce positive effects on the irradiation lobe distortions and on the whole system efficiency.
A low SWR is a necessary but not sufficient condition for achieving maximum system efficiency.
The example calculated in example shows the trend of currents and phases on a 2-meter metal support..
The 27VJ SmarTech is completely insulated from the pole. Currents, phases and the resulting irradiation solid are not affected by the presence of the supporting element, thus maintaining the catarreristas of the antenna design.
2. ANTENNA WITH INSULATED POLE BETWEEN THE MATCHING LINE CONDUCTORS
The mechanical-constructive advantage of this configuration presents as many important electrical and therefore performance problems.
The lower part of the J antenna consists of a rigid two-wire line with constant impedance (in our case 450 ohm). This antenna part does not radiate but provides to impedance matching for a 50 ohm coaxial cable use.
On both two-wire line conductors, flowing currents have same and opposite sign values so that the resulting external electromagnetic field is obviously null.
However, RF fields between the two conductors are not null and the presence of a (relatively) large diameter metal object, even parallel to the conductors themselves, the support pole, represents a great interference element.
The simulation above, shows with great evidence that the pole is hit by the radio frequency field of the matching line. Currents induced on the support element allow unwanted radiation by the pole itself, causing identical consequences and considerations seen for the previous case.
|Gain||8.29 dBi @5m [16.4 ft]|
|Power rating||5 kW|
|Matching Method||2-wire 450 ohm line|
|PHYSYCAL AND MECHANICAL SPECIFICATIONS|
|Length||abt. 8m [26.2 ft]|
|Weight||3.7 kg [8.1 lbs]|
|Projected area [F=Flat - C=Cylindrical]||0,15 m²|
J-POLE VERTICAL for 27MHz (27VJ)
- Brand: SmarTech Innovations
- Product Code: 27VJ