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)
