To be able to receive at 500kHz  I had to kill the 500kHz  QRM source.
Yesterday  I used my modified to 475-500kHz "RANEX"  pocket radio  to search the
 the noise at 500kHz.  That QRM was covering 500kHz for more than a week. 
Constantly  50kHz wide and stable in frequency.
This time I searched at neighbours home  but nothing found.
This MW receiver is a great noise sniffler.
There are lot's of noise sources in a home to be found.
I found an new one a CD player in standby mode.

Back at the radio the 500kH noise  was  gone suddenly..
I switched the CD player back on but that was not it.

Nothing found but QRM was gone.

Then replaced the 1:9 transformer back to the original in the K9AY rx antenna loop.
This one has a small core with high AL. 
I tested a transformer with low Al   not trifilar but "normal" wound 1:9 
 In the hope getting better result but it was no improvement.
The K9AY does not work at 137kHz it starts to work at 500kHz the signals are always weaker than from the 160m TX antenna  inverted L  with 26m vertical leg.
 Measured 400uH- 50uH  taps           5 trifilar turns   
  Testing reception of OK0EMW at 505.084kHz  very weak but clearly a carrier
Still the 160 inv.L   performed better...
In 2010 also DI2AM in Rostock could be received much stronger then OK0EMW.
But could not hear DI2AM  possible QRT or QSY to 474kHz

WE6XGR  was transmitting last night again
I saw reception reports already by   G0KTN  and  SWL  F59706
No reports from DL this time.
very weak decodes  -25 to -30    I did see only a very faint trace at 499.500kHz.
I wonder why there are so few SWL's  in this WSPR mode
Those SWL reports are really noticed
Instant reception result on WSPRmet.org     what more could you want as a SWL?

much later when at sleep
between 01:40 and 5:30  very  weak decoding again
"stongest"  -21dB   al far far worse than in 2010 2011  When  WD2XSH/7 EM31JS could be decoded  still ODX 7830km for this band

 2012-12-17 01:40  WE6XGR  0.499500  -26  0  FN12  50  PA0O  JO33hg  5988