80m, 40m, 20m & 10m Off Center Fed Dipole Antenna

ANTENNA DESCRIPTION

The TZ-OCF-80 is an Off Center Fed wire antenna designed to permit operation on the 80m, 40m, 20m and 10m amateur bands. The antenna is ideal for local communications within 1000-2000 km of your location or for DX depending on how high the antenna is mounted and in what configuration. If you're new to the HF bands and want to try a bit of local ragchewing, why not experiment with this antenna first. Alternatively, when the antenna is mounted at height, and well in the clear, this antenna will permit DX contacts to be made on the 10m, 20m and 40m ham bands but especially the 20m band.

Because of end effect, your TZ-OCF-80 has been trimmed for resonance in the main phone sections of the 40m, 20m and 10m bands. This has the effect of having resonance on 80m a little low in the band (around 3.5MHz). However, this is the best compromise for all around performance of this simple, light weight, mulit-frequency antenna.

LOCAL QSOs

For local communications around your location within 1-2000km the antenna can be mounted in either a dipole configuration, low to the ground at heights of approximately 10m or so. For local QSOs the antenna is best mounted at a height of between 8m and 10m. Note at low heights, the impedance of the antenna on 80m will approach 100 ohms or less representing a VSWR of 2.0:1 or more. The antenna will still be effective but an antenna tuner may be required to present a better load to the transceiver. Best VSWR results are obtained when the antenna is mounted 15m or more above ground.

DX QSOs

For effective DX contacts the antenna should be mounted at least 15m above the ground at all points and be configured in a straight dipole configuration. At heights of 20m or greater the antenna will produce outstanding DX results on both 10m, 20m and 40m. At 30m or greater, DXCC on the these bands will only be limited by your own commitment to being there when the DX is! As the sunspot cycle improves, DXCC with 100w will be easily achievable using this antenna.

BLOCK SIZE & MOUNTING CONSIDERATIONS

For the amateur without much room, or dollars, or who has an XYL not keen on a big antenna and tower in the back yard, this can be a real opportunity. The wire and traps of the antenna are made from (blue or grey) covered PVC and painted to produce a minimal visual impact - as far as possible for an antenna! Most regulations in Australia permit a mast to be erected 3m above the tallest point of the building (primarily intended for TV antennas) but this ruling can effectively be used to get your ham antenna up at least 8m.

The ground space required for the antenna in a dipole configuration is 42.2m from end to end. Configuration in an inverted vee is NOT recommended or supported for this antenna. If your block is not large enough to support the antenna elements in a straight line, the element may be bent on the long end towards the ground to a configuration that suits your block shape and size. Do not turn in the horizontal plane - make the turn in the vertical plane as this reduces unwanted braid currents in the feedline.  VSWR may deteriorate in this instance but a tuner may be used and the antenna radiation pattern and efficiency will not be greatly effected.

Ensure that the feedline from the balun is dropped vertically from the feedpoint to the ground and run the feedline along the ground to the shack or operating position for as long as possible. If necessary a further feedline choke may be inserted in the feedline if undesired feedline currents present a problem at your installation.  Ideally, the feedline should be run vertically downwards until it touches the ground to reduce the probability of undesired feedline currents and radiation. This helps to reduce or prevent TVI.

Note that due to the proximity of the ground, end effect, etc, the VSWR dip point of the antenna will vary with the configuration selected and the height above ground. This is a matter of physics! Anyone who tells you otherwise does not know what they are talking about. Changing the height above ground can improve or degrade the VSWR or resonant frequency of the antenna. Each installation will be slightly different and yield slightly different results

ANTENNA DESIGN AND COMPONENTS

The TZ-OCF-40 is one of the most simple yet effective multi-frequency antennas. Light weight but strong PVC covered, multi-stranded copper wire is used for longevity and low resistive losses. The antenna does not use any traps.

A dual core 4:1 current mode (Guanella) balun is used to provide excellent choking impedance to unwanted external surface braid currents on the feedline. The balun also provides the necessary 4:1 impedance ratio transformation to permit low VSWR over the frequency bands of operation. The Rippletech TZ-230D-4M balun is supplied with this antenna. There is no need to purchase a separate balun, and Rippletech never encourages feeding a balanced antenna using coaxial cable without a balun installed. Note some suppliers, quote and supply antennas without a balun (only an insulating block and UHF style SO-259). Make no mistake, use a balun and get optimum performance from your antenna system.

Stainless steel end terminations are provided so that the user can attach suitable ropes to secure the antenna to its end supports. Stainless steel fasteners are used throughout.

PORTABLE OPERATION

The TZ-OCF-80 is also a fantastic antenna for portable operation. Tied between two trees a suitable distance apart, will yield excellent results, with a minimum of effort. The antenna is very lightweight and easy to support in trees or small support structures.

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