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)
