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)
