Greetings to you, Nobutoshi.
I am operating WSPR on 30m every day in Vancouver, Canada, using +13 dBm. I see your strong signal on my waterfall, but most of your transmissions are NOT decoding. When I see a successful decode, your SNR range is -20 to 0 dB.
Many of your transmissions are terminating before the proper duration of 2 minutes. This is very strange. I have attempted to compensate by setting my PC clock slightly fast, but this has not helped.
What is happening? This does not appear to be a QRM problem. Perhaps you need to synchronize your computer to JJY/WWV more often.
I would be very excited if you decoded my QRPpp signal. It would be my second WSPR DX. I think it is possible, because I have used my QRPpp station to work DX on CW and RTTY.
Anyone else care to comment? Thanks.