The first QSO on LF took place on 20/03/2010, using normal hand keyed morse code, with Dale VK1DSH. Dale is only about one wavelength away - still a very significant milestone for me.
The following spectrogram were produced on 01/09/2010 by VK2DDI's grabber. We started with QRSS30 and 50 W but realised that signals are pretty strong, so I switched to QRSS3:
Then I lowered TX output power to 25 W:
Signals were visible at 25 W, so I reduced power even further to 9 W!
Last Sunday 14/03/2011, I attempted to transmit a WSPR beacon on 137 kHz using as a PA a TDA1517 based audio amplifier from a cheap PC speaker set. I used only once channel and I added a 4 Ohm to 50 Ohm impedance transformer at the output. Other than that, the amplifier was not modified in any way. Oh, I also added a fan to cool it down. Even though 137 kHz is way out of the little audio amplifier's frequency response, it still produced a stable 1 W signal. Out of that 1 W, less than 0.1% would be radiated. But hey, why not try it anyway!
The result was quite amazing. My signal was received in Mt. Berri, some 150 km away from my QTH! Here is a snapshot of David's (VK2DDI) WSPR screen:
The experiment took place in early afternoon, so this was strictly ground wave. Try that on ANY other band if you like! This really is amazing and it is no surprise to me why this part of the spectrum was so valuable in the past.
Who says LF is difficult!