Congrats Markus and thank-you for providing the interesting details.
73
Joe VO1NA
On Sat, 6 Mar 2010, Markus Vester wrote:
Dear LF,
on two evenings this week, I have transmitted an 8.97 kHz signal from my LF
Marconi at home, and attempted to receive it at various locations. The
experiment was very similar to the one in April 2003, but with a moderate
improvement in ERP and FFT bandwidth. Now on both occasions, the carrier could
be detected at a distance of 12.1 km:
http://www.mydarc.de/df6nm/vlf/vlf_12km.jpg
My transmit antenna is relatively small, about 220 pF and 9 m effective height
at 137 kHz. Assuming a 20% reduction due to shielding, radiation resistance
would be around 74 microohms at 9 kHz. The 1.4 henry loading coil is about 30
cm long by 12 cm diameter, and is split into seven slightly conical sections,
partly inserted into one another
(http://www.mydarc.de/df6nm/vlf/9kHz_aircoil.jpg). Each section has 700 turns
of 0.2 mm enameled wire, total DC resistance is 830 ohms. Fine tuning is
achieved by shifting a thick block of ferrite into the last section. Using a 35
W car-radio audio amplifier and a 1:32 ferrite transformer, I now got up to
0.135 A and 11 kV rms at the antenna. Radiated power was thus approximately 1.3
uW (EMRP).
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