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