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From: Stefan Schäfer <[email protected]>
To: [email protected]
Sent: Mon, September 27, 2010 9:07:48 PM
Subject: VLF: Earth antenna DX on 8970 Hz confirmed

VLF,

Last saturday, Michael Oexner has successfully and undoubtly received the message i transmitted on the 600m spaced earth electrode antenna on 8970 Hz. His RX antenna is a PA0RDT design. SpecLab was used to receive the signals.

The applied TX power was about 250 W and the mode was DFCW-600. The antenna current was measured to be 530 mA. The QRN was reasonably low although it could have been better to transmit 2 hours before.

There are 2 screenshots in one picture: The upper (in UTC) shows the result with a SpecLab internal band filter (BW= 6 kHz, centered arround 9 kHz). A clipping level of 6 dB was applied + the noise blanker set to 0.002/9/0.05. The lower (in UTC+2h) shows the same signal without using the internal SpecLab filter and without clipper, so just the blanker. You can see the difference! This means, as impressive demonstrated by Paul Nicholson on http://abelian.org/vlf/ss100801/, that bandfiltering is very important on VLF. Mostly it means to exclude the mains hum and the strong MSK transmitters. A too narrow filter is not optimal since the blanker has to "see" the QRN to blank it then. Thus i modified my VLF grabber circuit and have thrown out the 9 kHz band filter.

After increasing the earth antennas efficiency soon, the signal should be up to 10 dB stonger :-)

73, Stefan/DK7FC