136kHz WSPR on an active antenna

Just tried a PA0RDT designed active antenna (but just used an MPF102 and 2N3904 instead as these devices were to hand) with 1m of wire, later just a small piece of copper laminate (see picture), indoors taped to the window and have just spotted M0BMU running 200mW ERP on 137.45kHz WSPR. Amazing that this can work so well. The antenna looks useful for VLF through to low HF. See also
http://carconline.blogspot.com/2009/05/pa0rdt-active-antenna.html and http://carconline.blogspot.com/2009/05/pa0rdt-active-antenna-continued.html