LFA and OWL antennas represent a major advance in the Yagi design art
20 years ago K6STI's Antenna Optimizer (AO) and Yagi Optimizer (YO) were revolutionary products that transformed antenna design. Tom Schiller was an early adopter and the C-3 was the first fruit of a wave of high performance trapless multiband antennas and direct 50 ohm feed monobanders that earned a world wide reputation for performance.
Now the G0KSC LFA (Loop Fed Array) and the G0KSC OWL (Optimized Wideband Low Impedance) represent a major step forward in the evolution of the Yagi antenna.
G0KSC models use the very latest Numerical Electromagnetic Code (nec 4.1) embedded into a custom designed computer optimization package utilizing the very latest Particle Swarm Optimization techniques. In conjunction with the employment of self-learning algorithms, the results are the breath taking performance and patterns that can be seen from the full range of OWL and LFA Yagis from FORCE 12.The self-learning algorithms and Particle Swarm Optimization engines enable the G0KSC optimizer to get better and better each time it produces a model.
Each antenna is the result of billions of iterations conducted by multi-processor CPU’s over many days, week and months. These designs would have taken years to produce even if the G0KSC antenna optimization techniques had been available during the 80’s or 90’s.
The G0KSC Loop Fed Array (LFA) Yagi
The LFA Yagi has been designed with the serious VHF/UHF operator in mind. Never-seen-before Sky temperature and G/T figures* prove the LFA is the quietest antenna available today for any given boom length. Ensuring the operator can hear as well as be heard!
The LFA does not use a dipole at the feed point of the antenna. Instead it uses a large, rectangular loop laid flat on the boom between the parasitic elements and this loop serves several purposes. First of all, a closed loop helps to reduce the pickup of any man-made noise/static. Next, it helps to broadband the antenna resulting in the LFA producing some very wide, low and flat SWR curves. Finally its size in both X and Y plots are dynamically altered by the G0KSC optimizer in order to maintain a natural 50 Ohm feed point impedance ensuring any connection losses are kept to an absolute minimum.
The fact the loop is both the radiating element and matching device ensures that any pattern viewed within any antenna modeling package (such as EZNEC) is exactly what is produced by the antenna when built (corrections for boom etc. in place where necessary). While these packages provide a function to allow for matching units (such as hairpin, Gama, T match etc.)to be modeled, the limitations within the antenna modeling engine do not allow for them to model the physical matching unit attached to the antenna, only the effect such a device will have on the antenna impedance. This means the ‘real-world’ pattern may not be anything like the computer predicted model.
G0KSC recently proved the effects these matching units have on the final built antenna within an article published in DUBUS Magazine (February 2010) where a 7 element 2M Yagi lost 10dB Front to back (F/B) and .5dB forward gain by adding a hairpin match ‘after model’ (verified within EZNEC Pro/4 using nec4.1). Needless to say, any such issue does not occur with the LFA. If you want the best looking patterns, high F/B ratio and low-noise wideband antennas with excellent levels of gain that can hear weak signals, look no further than the LFA Yagi exclusively available in North America by Force12.
If you want to hear the weakest signals and RF input limits equal to the coax feeding the antenna, then the LFA is your choice.
The G0KSC Optimized Wideband Low-impedance (OWL) Yagi
It has long been known that a low impedance antenna produces the best performance figures. However, the down side to low impedance Yagis is the narrow band and twitchy nature that comes with it.
The lower the impedance a Yagi becomes, the more unstable (in wet and icy conditions) and narrow band it becomes too. For this reason, commercial manufacturers have to try to compromise by not going too low in antenna impedance (perhaps 20 to 30Ohms) sacrificing a little gain and F/B in order to not be so twitchy in wet and icy conditions and hopefully, maintaining a little bandwidth too. The OWL has removed the necessity to produce compromise antennas, and has allowed impedances as low as 12Ohm to be used within very wide band antennas hence capturing the benefits of 50Ohm and Low Impedance Yagis all in one antenna!
As with the LFA, the advanced computer optimization techniques of G0KSC employing both the very latest Numerical Electromagnetic Code and Partical Swarm Optimization technology has resulted in a very low impedance antennas that are wideband to be produced .
How about the issue and effect on pattern matching devices have on ALL Yagi antennas? By modeling and experimenting with EZNEC Pro/4 which has the most current electromagnetic code embedded (the same as the engines within the G0KSC Optimizer), G0KSC has established that any matching device should stay at absolute center of the boom and not extend along or near any elements further than the width of the boom. Our simple but powerful matching arrangement allows for this to happen and allows for up to and above 2KW to be used!
‘Breath taking performance from short antennas’ is the motto of the G0KSC OWL Yagi. More proof needed? On 27th February 2010 ZL1RS pointed his compact 32’3’’, 8 element 50Mhz OWL Yagi to the moon with only 72 watts output. He was heard by Lance, W7GJ with a best signal of -26dB. If it is the best performance you want from your Yagi, the OWL is going to be hard to beat!
Which do I need, the LFA or the OWL?
First of all, when selecting an antenna, simple gain and F/B figures should not be all that is considered, especially at VHF and UHF. Bandwidth, Sky temperature and G/T are important criteria too for antennas being used at 2M. More importantly, if a manufacturer does not publish SWR and pattern plots for their antennas, ask yourself why? Perhaps you should even ask them why too. Would you buy your next car without seeing it?
In 2010 there really is now just a 2 horse race if you want an(the best performing) antenna for 10M and up. Which is best for you the OWL or the LFA?
While the OWL is modeled with quiet clean patterns being a top priority, in general they are just beaten into second place by the LFA. However, quite often the OWL just passes the LFA for out and out gain. This said, take a good look at the available LFA/OWL antennas at the band and boom length you are interested in. Attributes vary slightly and sometimes one is just a little better than the other. However, a good rule of thumb is this; If you are in a city location with a lot of man-made noise around you, the LFA will help reduce this and help you hear what you want to hear. If you have a fair amount of open space and very little or no man-made noise, then the OWL maybe for you. One last recommendation; check the Force 12 site regularly, we are adding new and updated models all of the time. The antenna of your dreams maybe added today!
Mark Hooper, N5WEB & Justin Johnson, G0KSC
*Google search VE7BQH for a full list and comparison of antennas and an explanation of both Sky Temperature and G/T.