Friday, 28 August 2015

"FORKER" 5/8 over 5/8 Vertical for 70Mhz.

A highly efficient 2 x 5/8 wave FORKER Vertical antenna for the 70Mhz band with excellent wind handling ability and 5KW rated.

Justin Johnson G0KSC become well known for his LFA (Loop Fed Array) Yagi antennas with their exceptional low-noise performance. He has always been mindful of potential losses caused by matching devices and their placement within antennas. Some of the associated issues of matching devices include, power limitations on TX, noise induction on receive and alteration of the signal/antenna pattern.
This G0KSC designed 5/8 over 5/8 does not use any 'lossy' coils or traditional forms of matching devices. It uses a double-J arrangement or 2 vertical radials that run parallel to the main radiating element in order to achieve a balanced, 50 Ohm input. Unlike the J-pole which has a slightly directional pattern, the double-J or Fork type feed arrangement (hence the FORKER name!) produces an almost perfect symmetrical radiation pattern. This too can be seen in the plots listed in the 5/8 overview at the bottom of this page. Without traditional matching coils/devices, radiating efficiency remains higher than most competitive products.
The InnovAntennas 2 x 5/8 has been designed in order the pattern angles slightly downwards (11 degrees) in free space (above ground placement will alter this but radiation angle will remain low).This ensures even when this antenna is installed very high up, it will provide excellent near and far-field coverage.

The antennas are constructed with the best quality materials in order that the best mechanical construction can be achieved, not the cheapest and most profitable! Even a digital calliper is used (with an accuracy of .01mm) to measure the elements during production to ensure they are within tolerance, ensuring they work as well as our software model predicts.
1.    Marine grade Stainless Steel Fittings
2.    Original Stauff insulator clamps
3.    Mill finished for highest levels of accuracy

Gain: 5.12dBi/2.97dBd @ 70.1MHz @ -11 degrees in free space
Gain @ 10m above ground: 8.41dBi/6.26dBd @ 4.2 degrees
Gain @ 20m above ground: 9.44dBi/7.29dBd @ 2.5 degrees
Maximum Power handling: 5KW
SWR: 1.02:1 @ 70.1Mhz - 1.5:1 @ 70Mhz - 1.5:1 @ 70.5Mhz (Centre frequency can be adjusted from 69.9 to 70.5Mhz with 2Mhz1.5:1 bandwidth
longest Section Length: 5.13m 
Weight: 4.52Kg 
Wind Loading: 0.1 Square Metres
Wind Survival: 160KPH 

This antenna has been modelled both electromagnetically and mechanically in order to ensure it will stand up to adverse weather conditions very well. Both element diameter and wall thickness is tapered to ensure best possible survival characteristics and high quality components (including marine grade stainless steel A4/316 hardware) are used throughout. 
The 2 x 5/8wl FORKER vertical for 4m uses no coils or loading to ensure maximum radiated power. A solid rod delay-line is installed between the upper and lowers 5/8wl elements and the FORKER twin stubs at the base ensure this antenna has a 50 Ohm impedance.

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