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EME Activity started in 2 meters around 2008 and the first QSO was completed on 15th November 2008 with KB8RQ thanks to JT65 digital mode . The station set-up was quite modest and included a TS2000 with 100W, a 9 elements yagi ( WIMO ) and a DB6NT 144 Mhz preamplifier.
The 9 elements allowed a gain of 12.4dBd ( 14.55 dBi ) and was enough to make QSO with the big guns . The attempt to couple two antennas ( fig. 1 ) was not very successfull as , due to space constraints, it was not possible to have optimum spacing .
The expectation was to gain 2.5-2.9 dB, but reality was about 1.5 dB with more ground noise !
The explanation is that two yagis must be spaced enough to avoid to cross the two effective aperture ( Ae ) and in the case of a Yagi with 12.4 dBd this spacing is roughly 3 meters .
The effect of narrower spacing was the increase of the side lobes and, consequently, the capture more ground noise.
This was also confirmed with EZNEC ( http://www.eznec.com ) ( fig. 2 ). A VNA ( DG8SAQ ) analysis showed some shift of the main frequency and a second resonant frequency ( see fig. 3 )
The two 9 elements Yagi coupled with too narrow spacing .
EZNEC analysis of the two 9 elements Yagi showing side lobes around 45 deg.
DG8SAQ VNA analysis showing a second resonant frequency and some shift of the main frequency .