To explore the possibility of further two-way VLF contacts from my home antenna, I have conducted a test in MFSK-37 mode this morning. I was hoping to reach 0.42 mHz ("6000") grabbers using UT-synchronized half-hour dashes. Similar to an earlier kite experiment, I used absolute frequency encoding of characters in 1 mHz steps (0 = 8970.000, 1 = 8970.001, ... 9 = 8970.009, idle = 8970.010, A = 8970.011, .. Z = 8970.036 Hz).
The plan was to transmit my complete callsign in 2.5 hours between 8:00 and 10:30. Unfortunately DHO locking failed during the first two characters, which came out some 9 mHz low. Attached image shows what was actually sent according to my "monitor", which is a high harmonic of the transmitted VLF signal accidentally aliased into the LF TA window.
I was pleased to find all the dashes showing up clearly as bright dots on the OK2BVG "6000" grabber, and even left visible traces in his "600" window. As I had also received Lubos' transmission last weekend with a good margin in 0.48 mHz, a two-way QSO between us would probably be feasible within a few hours.
Paul Nicholson's 0.278 mHz super-sensitive spectrogram also shows the transmission at 120 degrees azimuth, even though the dashes were really too short to reach full SNR in this bandwidth.
Results on the DK7C grabber were not quite as good, with only a single clear dot on .006 Hz. This may partly have been due to the previously experienced daytime minimum at our distance (180 km). Nothing distictive was visible at OE3GHB, who is at similar distance as OK2BVG, but seems to have suffered from a bit of local QRM at the time.
Again we find that a great deal is possible with very modest means...
Best 73,
Markus (DF6NM)
