Hi Stefan,
Your RX antenna looks very similar to the K9AY which has been used
Very successfully by many LF /MF operators for years.   It is a little difficult for me to picture the details as I am looking at it on my phone.  An excellent web site for such antennas is Dallas Langford's Yahoo group, he has spent years optimizing similar antennas and has achieved results superior to beverage antennas with some of phased loops.
I will send a link if you are interested when I get home.
73 Warren K2ORS

73 K2ORS

On May 13, 2012 1:11 PM, "Stefan Schäfer" <[email protected]> wrote:

Hello Group,

I've just started to play a bit in EZNEC, trying to simulate a receive loop antenna for the new YV7MAE grabber. http://dl.dropbox.com/u/74746618/LF/YV7MAE_LF_Grabber.html ... still using a wire receive antenna with excellent results but now a directional antenna is needed.

So i modelled a loop with a possible shape and a ground connection. Then i added a R on the far end of the source. The results of the elevation and 3D plot are surprising good. Maybe i have done a mistake in modelling? Optimal performance was obtained at R = 8 kOhm. This resulted in the best F/B and beamwidth... Results of ZENEC are here: http://dl.dropbox.com/u/19882028/LF/Cardioid%20for%20LF.png

Any ideas, experiance or advice?

I guess a preamp is needed when such a antenna is used. The typical 1:9 un-un does not look useful for me...

73, Stefan/DK7FC