The RSGB Newark Hamfest in just a few weeks from now will see the launch (through InnovAntennas) of the next step forward in G0KSC Yagi development. Enter the LFA-R.

The 4R5 - 5 element 70MHz LFA-R on a 3.45m boom providing over 11.4dBi gain

The LFA-R started form as an HF antenna, one of the many new antennas in the force 12 range. With a single flat, driven loop and one director, I was surprised just how much F/B was achieved along with excellent levels of gain too. Many element versions where not practical for HF so the experiments shifted to VHF and this is where the LFA-R really came into it's own.

The LFA-R uses a compact LFA loop at the back of the boom and has no reflector element at all. The arrangement of phase presents itself in much the same way as it does within an HB9CV. However, this loop is completely joined (or course) all the way around. Only director element follow the driven so on a 5 element version (such as the above shown example) you have 4 directors rather than the traditional 3 directors a typical Yagi would have. This, along with the driven element being moved further back on the boom that the traditional Yagi means more gain can be achieved. 

Once corrected, the LFA-R still produces aroudn 11.4dBi forward gain from this compact boom

 

This extra performance does not come for free, the antenna has a much narrower bandwidth than you might be used to seeing with my designs. However, I have spent time on establishing non-conventional stability with the use of electrically connected elements and 'thicker' elements. Time had to be spent on establishing correction in order to replicate model but as you can see from the below software prediction and final analyser results, this has been achieved with near perfection.

The EZNEC V5 Pro/4 output prediction for SWR on the 4m band with the 4R5

The AIM analyser results show lead-in and lead-out curves tracking almost identically to the software model

The LFA-R has been thoroughly tested too. In addition to having a 4 element 70MHz  (4R4) installed at the InnovAntennas factory this summer, other early adopters have installed LFA-R's too. CT1HZE has a 4R4 installed in Portugal (see a conversation between Joe and I on 4m with us both using 4R4's

 I was using the call of M0LFA which is the InnovAntennas factory call sign and also, using just the Electraft KX3 with internal 4m transverter with only 3 Watts output!). 

The 4R4 installed at CT1HZE above his large 6m LFA

In addition to the 4m examples, a new 6 element 6m has also been installed at several locations too. XE2X has a 6R6 for almost a year now that can be seen being installed by InnovAntennas/Force 12's own XE2K, Hector. Again, the 6m antenna really does pack a big punch for its size with around 12.2dBi on this relatively compact 6.5m long boom and yet still holds relatively respectable F/B too.

XE2K installs a 6R6 - 6 element 50Mhz LFA-R

This particular version has been made very HD with VDS (Vibration Damping System) element insulators installed on a large 45mm to 38mm boom. The boom itself tapering in both OD and wall thickness too in order that a guy system is not needed. SWR remains stable throughout as the new owner XE2X Jorge, can verify. Jorge also reported this as being the best 6m antenna he has installed to date! Take a look at the performance plots below.

A small amount of convergence correction is needed but still almost 12.2dBi is achieved on just 6.5m of boom

 

 

The 6R2 - 2 element 50MHz LFA-R measures just 51cms (boom). No excuses for not being on 6m now!

 

The 6R2 shows a very respectable SWR plot across the 'sweet spot' at the bottom end of the 6m band

 

Impressive! The tiny 6R2 really packs a punch and still has great F/B too!

 

So, if you want to see it in the flesh, come along to the RSGB National Hamfest in a few weeks time and here we will have a number of built versions on display. Before you ask, I will publish some designs for self-build but early on these will be by personal request only, if you want to build one, let drop me a line and we can discuss the requirement together.

More detailed coverage of the LFA-R can be found in the current issue of DUBUS magazine (3/2014) www.dubus.org

Until next time!

Justin G0KSC

 

 

 

Don't be misled into thinking you are buying something you are not.

Within this site I have provided a number of designs for self-build which allows hams to build antennas themselves that are as good or better than options they can buy. In the past I have sold the rights to a number of antenna manufacturers around the world to reproduce these public domain designs. However, these are my early work, they are older designs and while they work well, they are far and removed from the most current design releases and lack many of the enhancements of my most modern designs.

3.5 Years ago, I setup InnovAntennas with Bill AA7XT and through this company (and the now acquired Force 12) , we provide the very latest designs. The LFA-R, LFA2, LFA-Q the OP-DES and the latest LFA designs are only available through InnovAntennas, no one else.

My design work has slowed in the public domain but this is only because commercially it has been taken to new heights. We design and build LFA Yagis for government & defence applications both at home and abroad and recently completed an HF LFA Yagi array (multiple antenna stack) to be used as an over the horizon radar system for defence purposes.

Newly designed LFA Yagis are on service in the Middle East right now and even on destroyers off of the African coast where they help track pirate activity. So why select InnovAntennas Yagis if you are choosing to buy? One antenna is not the same as another and a good understanding of both electromagnetic design as well as the impact of any mechanical structure needs to be understood and appreciated to ensure performance is achieved. You can be assured of a fully rounded, fully finished product from InnovAntennas.

It does not just stop there either. The new range of LFA, LFA2 and LFA-R (LFA-R is an LFA Yagi modelled without any reflector element) produce very high levels of gain compared with the public domain versions on this site. However, much development effort has gone into ensuring design stability in addition to huge increases in gain over the publicly available designs, has been achieved. Why is this important? Anyone that has purchased and used a 'high gain' Yagi will know that often, the said Yagi is totally unusable when it rains (or is covered in ice)  as a result of inherent design flaws.

Above is a photo of a recently installed (June 2014) 5 element LFA-Q Yagis by InnovAntennas installed at G8VR. These LFA-Q's are just 4.3m long but individually they provide over 11.6dBi gain and do this with stability not seen in such high gain designs previously experienced by ham radio operators. Note the very strong mechanical structure of this antenna with an under-boom that provides 'upward' support in order that boom sag is completely removed. 

Now take a look at the below plots. The first image is the predicted impedance curve of a 30 element X-pol LFA Yagi on 432Mhz. X-pol Yagis have always been very difficult to get right, especially on 432Mhz. Impedance is compared in this plot and the second one (which is the built antenna analyser results) as impedance is the most sensitive parameter and shifts before anything else if the antenna is not right.

 

 

Software prediction of the 30 element 432MHz LFA Yagi

 

 Analyser measurement of the finished antenna

Pay careful attention to the above plots, not the lead-in and lead-out shape of the curve and exactly where the antenna sits. This is not just somewhere close, this is a near-perfect replication of the software model in the real-world. This is one reason commercial entities, governments and defence organisations are employing my services to design and produce their antennas and this is something you can share in too.

So is it just about cost? You decide but you can be assured that if you decide that you want to buy a Yagi ready-built, it will be the latest design and any support and set-up help will be provided directly by the antenna designer himself, i.e. Me!

Any questions within regards to your antenna requirements, be it station layout planing for a contest station or just how far apart your antennas on a single mast should be, I am happy to help.

Until next time,

Justin G0KSC

justin 'at' G0ksc.co.uk