Dear LF,
this morning, June 4th between 6 and 8 UT, Walter (DJ2LF) and myself (DF6NM) were able to successfully conduct a two-way contact (aka "QSO") on 8.97 kHz. The distance between us is 20.2 km, well outside
the reactive near field zone (lamda / 2pi = 5.3 km).
Both of us were using our small backyard Marconi antennas at home, for transmit and receive. Walter's antenna has 260 pF at an estimated effective height of about 5 m. He achieved about 370 mA current,
resulting in a radiated power of about 5 uW (EMRP). I also got 5 uW from 270 mA into 240 pF at about 7 m. I resonated the antenna using the same little "yoghurt coil" described a while ago, having 1.3 henry from 9 x 480 turns of 0.2 mm magnet wire, and a room-temperature
DC resistance of 820 ohms. Walter used a scaled up version of this coil, about 25 cm diameter and 60 cm long, consisting of seven polypropylene household buckets inserted into one another. Each bucket has 460 turns of 0.4 mm wire on it, about 320 ohms total
DC resistance. Each of us applied approximately 100 W of "RF" power from a car-HiFi amplifier.
Reception was done by soundcard, without preamplification. We set Spectrum Lab to 0.95 mHz FFT bandwidth, with noise blanking on, and samplerate tracking based on the German 23.4 kHz MSK signal. We chose
to transmit 30 minute dashes, separated by 15 minute quiet intervals to allow for FFT processing delay.
We employed a special "micro-QSO" format, which was designed to exchange the minimum single-bit report and confirmation in only three turnovers, each containing a single dash. Station identification
was by frequency alone, with preassigned pairs (8969.92 / 8970.02 Hz for DJ2LF, 8970.0 / 8970.1 Hz for DF6NM). Generally the lower frequency was assigned to a negative response (ie. "not confirmed"), whereas the upper one is positive ("received ok").
DF6NM started by transmitting a carrier on his lower frequency, from 4:00 to 4:30 UT. This was indeed seen by DJ2LF, who replied on his upper frequency from 4:45 to 5:15, reporting positive reception.
Then DF6NM confirmed reception on the upper frequency from 5:30 to 6:00. The whole procedure took two hours.
Attached are screenshots from both sides. Unfortunately the QRN level this morning was much worse than we had hoped for, with active thunderstorms in South Italy, Poland and Belorussia. To my surprise, our
dashes still made it through and were unambiguously visible, with an estimated SNR of 6 to 8 dB. Walter's signal can actually still be seen between my own dashes on my VLF grabber
http://www.mydarc.de/df6nm/vlf/vlfgrabber.htm .
As far as we know, this was probably the first two-way amateur QSO on VLF, using truely radiated fields. Another dream came true...
Best regards,
Markus (DF6NM)
