G4CQM 50Ω Direct Feed Low Q Low Noise Yagis


G0KSC 2M 8LFA Reality Check!...

Justin G0KSC published design information for his Low-Noise 'Urban' 8 element LFA Yagi for 144MHz on 25th August 2009. He has made many claims for his LFA Loop, and for a while many hams were taken by its appeal!

Meanwhile Martin DK7ZB carried out his own tests/experiments with help from Sven SM7DTT and others to see if a 12.5Ω yagi with Split Dipole or Folded Dipole could deliver similar performance. Design information and final results can be seen here: The redesigned 8LFAD with a simple 12,5-Ohm-Dipole or a Folded Dipole.

The challenge for me personally was to see if a 50Ω Direct Feed yagi design with a simple Split Dipole could equal the LFA?

During my six year long research project I have made significant improvements to my designs with help from several fellow Radio Amateurs who were prepared to give my designs a go! The results seen below speak for themselves...

Click on images for full size view, opens in new window!

G0KSC 2M 144MHz 8 element LFAG4CQM 2M 9 element WA9XX
G0KSC 2M 144MHz 8 element LFAG4CQM 2M 9 element WA9XX
8LFA seen in K6STI's AOP at 144.1MHzWA9XX seen in K6STI's AOP at 144.1MHz
8LFA seen in K6STI's AOP at 144.1MHzWA9XX seen in K6STI's AOP at 144.1MHz
8LFA seen in K6STI's AOP at 144.5MHzWA9XX seen in K6STI's AOP at 144.5MHz
8LFA seen in K6STI's AOP at 144.5MHzWA9XX seen in K6STI's AOP at 144.5MHz
8LFA Vs WA9XX Azimuth 144.1MHz8LFA Vs WA9XX Elevation 144.1MHz
8LFA Vs WA9XX Azimuth 144.1MHz8LFA Vs WA9XX Elevation 144.1MHz
8LFA Vs WA9XX Azimuth 144.5MHz8LFA Vs WA9XX Elevation 144.5MHz
8LFA Vs WA9XX Azimuth 144.5MHz8LFA Vs WA9XX Elevation 144.5MHz
8LFA SWR 144-146MHzWA9XX SWR 144-146MHz
8LFA SWR 144-146MHzWA9XX SWR 144-146MHz
8LFA Average Q-factorWA9XX Avearge Q-factor
8LFA Average Q-factorWA9XX Avearge Q-factor

VE7BQH style comparison at 144.1MHz (* 4 x yagis)...

Tsky = 287K Tearth = 5126K (Residential = 12 dB)
Design IDλBoom
(m)
BW
Az°
BW
El°
Gain
(dBi)
F/B
(dB)
* Ta (°K)
@ 30° Elev
* G/Ta (dB/°K)
@ 30° Elev
DEQ-factor
(Avg)
8LFA1.793.729424813.1825.50464.2-7.65LFA Loop21.14
WA9XX1.793.725424813.1024.92449.7-7.49Split Dipole19.76

 

Antenna Files...

8LFA.ANT
WA9XX.ANT

 



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