Re-hello Jochen, I will "comment" would you said : ------------- a small patch of PCB, about 2*2 cm will be sufficient if the antenna is designed on the PCB as part of the layout. The centre of the spiral can be connected on the otherb conductor side of the PCB, but only a small line, NOT a groundplane (This would help your problem all right, because ALL transmitting would be next to Zero...). Alternately, you can try a small cylindrical coil of standard enameled copper wire. This coil can bhe so placed that the magnetic field will cause less interference in one preferred direction... you have to experiment with the size, about 3mm diameter and 10 loops will do the trick if range is not paramount. Feel free to comment... Jochen DH6FAZ jf@detektor.de ---------------- For me, it is hard to add the patch (2x2 cm) since I lack drasticaly of place inside by box (I have the 12v cell, a switch, the coder, the hybrid Tx ... -> So, I will have to try the "cylindric coil" (I already thought of it). I thought of a coil with a wire length equivalent to the lambda / 4 i.e 18 cm (at 433 MHz), that would rather drive to more than 10 loops on a 3mm diameter ... My other inquiry is about the connexion of the antenna / coil : do I have to ground the other side of it ? I have seen those designs but a wonder : with a lambda / 4, the other side is at a max of the wave, so not to be grounded ... that should only be done with wave minimum at the end (lambda / 2) ... Do I make a mistake in my thinking ? Any comment ? Thanks P.S.: My aim is only some meters (<10) with a 12v supply ... _______________________________________________________ Jean-Yves SEYLER Opto-Electronics Department - BPi 2101 Phone : 33+ (0)5.61.28.18.52 FAX : 33+ (0)5.61.28.18.15 E-mail: Jean-Yves.Seyler@cnes.fr __ __ __ __ / | \ /__\ |__ CNES : French Space Agency \__ | | \__ __| Centre Spatial de Toulouse \\\\\//// CNES - 18, Avenue Edouard Belin / ^ - \ 31401 TOULOUSE CEDEX (FRANCE) ( (o) (o) ) _____________________________oOOO_____(_)_____OOOo_____