This kind of antenna is supposed to provide up to 2dB gain over the dipole. I was curious to check reception on weak semi-local stations (abt 200 km from home) to confirm there is an improvment. But ... this dis not happen

The only explanation could be I used 50 ohm coaxial for the downlead, instead of 75 ohms.
The receiving element itslef was made of (insulated) copper (1.5mm diam).
Could this explain its desappointing performance ?
Next, I plan to build a rectangle loop, providing 1.5dB more compared to the square and / or 50 ohms impedance, according to http://pa0fri.home.xs4all.nl/Ant/Quad/quadeng.htm