The ability to send two different radio frequencies in a helical construct= =20 allows a greater concentration of signals within a band.=20 I think the research was performed by the Swedish Space Institute, but the= =20 link to them is dead. Colin cdb, 3/07/2009 =20 -- colin@btech-online.co.uk --=20 http://www.piclist.com PIC/SX FAQ & list archive View/change your membership options at http://mailman.mit.edu/mailman/listinfo/piclist .