Vortex ‘Slim Jim’ Vertical Antenna – HF 24.9Mhz (12m band) Amateur



Vortex 'Slim Jim' Vertical Antenna - HF 24.9Mhz (12m band) Amateur

Vortex 'Slim Jim' Vertical Antenna - HF 24.9Mhz (12m band) Amateur

£275.00 — £380.00

Product Code – 24-SLIMJIM

A Vertical Wideband Antenna for the 24.9MHz (12m) Amateur band.
The Vortex ‘Slim Jim’ Antenna consists of a single element, one half wavelength long radiator with a quarter wave parallel feed-line tuning stub. The half-wave section is then folded back on itself towards the stub at a distance of approx 0.44 of a wavelength. At the base, the quarter wave matching stub is very similar to that of the J-Pole. The antenna is very easy to assemble and matching is easily accomplished by moving the feed-point up or down the lower sections of the tubes. This has an added advantage that tuning can be varied over a fairly wide frequency range by adjusting the feed-point location which is easily done. This also gives the user finer control over the impedance and match.

The antenna is end fed and generally has an omni-directional radiation pattern although there is a slight bias in directivity towards the ‘Stub’ side of the array as shown on the EZNEC simulation. The antenna requires no ground plane or radials. Slim Jim antennas have two very desirable characteristics. Firstly the angle of radiation is exceptionally low. During modelling, a Slim-Jim for the 12m band antenna at 10m in height above the ground had a radiation angle of only 9 degrees above the horizon making it an excellent base antenna for longer distance contacts. This reduces even further if the antenna is mounted higher. Some vertical antennas may exhibit higher gain figures, but the radiation angle is normally much higher – putting most of your power skywards rather than across the horizon. The antenna by its nature is also wide-banded with a 2 to 1 SWR bandwidth of over 2.8MHz. This version will cover the whole 12m band with ease and will also cover some of the lower end of the 11m band (26Mhz). As with all Vortex Antenna Systems – we build to last.

Slim Jim antennas should include a 1 to 1 ‘Choke Balun’ close to the feed-point, which prevents feed-line radiation. A simple and cost effective solution is to wind a small length of coaxial cable around a former. There are many examples online, but we found wrapping 6 turns around a 50 mm fibreglass former did the job. Vortex can also supply a larger commercial version of this if required using commercial grade ®Westflex 103 Coaxial Cable .
A Vortex Antenna Systems premium ‘Ferrite Core Choke Balun’ (Sealed to IP67 rating) is also available as an optional extra.

No Knowledge of Antennas? Our 24.9Mhz Slim Jim antenna is pre-tuned from the factory and all set-up measurements are included. However the system is fully adjustable should the user require to finely tune the system for their own requirements. We include a full set-up instruction sheet with each antenna.

All Vortex Antenna Systems Slim Jims’ use heavy duty components and hardware including M10 stainless hardware, heavy duty Stauff polyamide and aluminium clamps as also used in our lower frequency base antennas. The main element section of this antenna is supplied with genuine VORTEX 6082-T6 or *AA6082-T6 Aluminium with each section telescoping into its counterpart. The feed to the antenna is via a 75 ohm matching transformer stub which is weatherproofed.

Images show the 10m version to give a basic idea of construction.
Lower frequency antennas are scaled up as required

See info below for mechanical and electrical details

  Vortex ‘Slim Jim’ Vertical Antenna – HF 24.9Mhz (12m band) Amateur

Band(s):  12m (24.9Mhz)
Element Material:  6082-T6/*AA6082-T6
Boom Material:  6082-T6 box section aluminium
Gain:   4.28dbi at 10m in height
Feed:   75 ohm cox stub
Matching:   75 ohm cox stub positioned for best match
Rating:   2kw
Typical Radiation Angle:   9 Degrees at 10m in height. Even lower at more height
Element Clamps:   Stauff (Germany) – heavy duty polyamide series
Antenna Weight:   10kg
Antenna Height:   7.25m
Bandwidth:   Covers the whole band at 1:1 SWR or better
Hardware:   304/316 stainless steel

*If available