What is special about a low-noise LFA Yagi?

The LFA design has a patent pending and all G0KSC designs are copyright. Any ham can build for their own use or those of a friend. Where profit or commerical gain exists, express permission of G0KSC must be sort. 

The Low-Noise LFA has been engineered to enhance the low-noise characteristics of the LFA to the maximum. Typically, Yagi antennas are designed with maximum forward gain in mind only and all other atributes of the antenna are secondary. As a result (and in my opinion) these most Yagis are similar in their design and configuration to an over-driven amplifier. as the last few points of a dB are squeezed from a design, unwanted lobes in all planes increase drastically.

So what, as long as I get the best gain, right?

Sure, you get maximum gain you can for a given boom length. However, it is likely that you will have two more secondary lobes in the forward plane too. This may not be a problem in your location but the possibilities exist that you could cause more TVI than you would like. additionally, the front to back ration can reduce too and most important of all, nasty lobes in the elevation plane (straight up and down) grow to a very large size. again, you may think this is not a problem but these 'gainy' lobes will ensure you will receive maximum infererance from appliances aroud the home (and your neighbours too) as welll as cause maximum interference.

 The above is the elevation pattern of an 8el DK7ZB Yagi for 50MHz. The alarmingly large lobes you see in the image are the straight up and down lobes producing huge gain in receiving interference and giving it too, around the home. This is one reason most antenna designers and manufacturers do not publish elevation plane antenna plots

The above image is the same DK7ZB 8el Yagi for 50Mhz with the plot pattern (azimuth of horizontal). However, you will note it still has two large side lobes in the forward plane.

Another elevation plot of a DK7ZB antenna, this time a 5 element version for 50Mhz. Note the huge Upward and downward lobes.

So what else will having more than just one 'wanted' lobe do?

Imagine you are straining your ear to hear that wanted 'DX' and have your beam pointed in the right place. However, conditions are good and there are closer stations in most directions coming in. The neighbours have their noisy ADSL routers active and one of them has his plasma TV on too. the DX is at S2. A pretty good signal and should be Q5. However, your noise level is S2 too!

So, what is the cure?

The Low-Noise LFA Yagi! Take a look at both the elevation and azimuth plane of these example 50MHz antennas.

The is the Horizontal or Azimuth plot of a 6el 50MHz LFA Low-noise Yagi. Note there are no unwanted lobes, just one, clean forward lobe.

Now for the elevation pattern, Where are the huge lobes? Maximum suppression of the upward and downward lobes ensures a quite antenna that will ONLY receive signals from the direction it is pointing. Not the Neighbours TV or ADSL router! Interference will be reduced too by using this antenna.

As antenna sizes increase, Elevation lobe get larger. However, with this 14 element LFA, any unwanted lobes have been kept to an absolute minium. 17dB forward gain and no unwanted lobes!

This is the azimuth pattern of the same antenna. Incredible pattern ha? Only available on the LFA low-noise antenna :)

Conclusion notes

All LFA Yagis are muhc lower in noise than standard Yagis. In fact, comparing stacked arrays for EME, nothing on the VE7BQH list comes anywhere close in sky temperature figures. However, I do not band all LFAs as low-noise. Only when maximum lobe suppression has been the objective of the design (and acheived) will I give the antenna that label. With such an antenna you can be assured that local noise pickup (accept in the direction your antenna is facing) will be greatly suppressed when compared with a traditional Yagi antenna and therefore, for Urban or city use, the LFA is the one to have.

I have far more designs than I have published on site yet so if you have interest in a design, let me know, I may have something I can send to you right back. Both imperial and metric sizing are catered for.

Enjoy the site and the LFA, you will not be disappointed!

Email me with any questions you may have.

A Low-Noise 'Urban' 4 element LFA Yagi for 50MHz

The LFA design has a patent pending and all G0KSC designs are copyright. Any ham can build for their own use or those of a friend. Where profit or commerical gain exists, express permission of G0KSC must be sought.

If you suffer with noise from living in the city, this is an antenna for you.

This antenna is another one of my  designs created to minimise the upward and downward lobes typically seen the the EL plane on Yagi antennas. By doing this, a drastic reduction in pick up of unwanted noise in City locations is the result. The double bonus is the likelihood of reducing transmitted interference too. But best of all is through having such a clean pattern as a single antenna, stacking produces excellent, un-seen-before results. Take a look for yourself. The following information presents single and 2 stack information

Single Antenna Performance

Free Space Gain: 10.38dBi @ 50.200MHz

F/B: 25.9dB @ 50.200MHz

Boom Length: 4 metres

SWR: 1.0.1 @ 50.150MHz - bandwidth 4KHz 1.5.1

Excellent pattern for a 4el with good gain and F/B too.

In line with my Low-Noise theory, near-field pattern is greatl suppressed to ensure lower city noise pick up.

By modelling a clean free-space pattern, the antenna performs well above ground too. This is 6 metres above average ground Radiation angle is 14 degrees and 15.39dBi and F/B is 26.58dB.

At 10 metres above ground, the single LFA produces a little more gain, and F/B becomes 26dB.

At 14 metres up the 4el produces a respectible 16.06dBi with F/B increasing to 27.21dB.

With two phased 4 element LFA's one stacked above the other, the Azimuth pattern remains very similar to the single antenna pattern as the Elevation pattern being compressed is what produces the additional forward gain. Up from 10.38 to 13.09 a near perfect increase of almost 3dB has been acheived. A little more can be achieved. However, pattern and lobe production is then greatly compromised.

The two stacked antennas look very different in the Elevation plane.

The reason for keeping the patern clean in free-space now becomes clear, one strong lobe with 9 degress take off angle is produced with 17.79dBi Gain and 25.51dB F/B with the bottom antenna at just 6 metres above ground. The top antenna is staccked 4.3 metres above the first.

At 10 metres up this array is starting to really shape up. angle of radiation has dropped to 7 degrees, gain has increased to 18.38dBi and F/B is now 22.79dB

14 Metres up and the array is starting to slow in gain increases but the all-important angle of radiation is now 5 degrees with increasing once more to 23.08dB.

Email me for more information on this antenna or 3, 4 stack information.

73 Justin G0KSC