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LF: Ferrite rod antenna - on-air testing

To: <[email protected]>
Subject: LF: Ferrite rod antenna - on-air testing
From: "James Moritz" <[email protected]>
Date: Sun, 28 Aug 2011 19:44:35 +0100
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Dear LF Group,

The QRN level on 136kHz has finally died away, and I was able to record the attached spectrogram, showing DK7FC calling CQ around 1755utc, using my prototype ferrite rod antenna. On the left of the spectrogram, the rod is oriented for N-S reception, and the background noise consists mainly of horizontal Loran spectral lines, plus some unidentified, low-level, local "mush". On the right of the spectrogram, Stefan's signal level increases as the rod is rotated for E-W reception. Here, the noise level is mainly vertical streaks due to sidebands of DCF39's FSK modulation. The black area at the right hand edge of the screenshot is where the ferrite rod was replaced by a "dummy antenna" inductor, and shows that the internal noise level of antenna and preamp is below the band noise level (by around 10dB).

The band noise seen with the ferrite rod is practically the same as seen with larger loop antennas under quiet conditions, so this practical test does show that a reasonably compact ferrite rod can give sensitivity limited only by the external band noise on 136k. In fact, there is some margin for making the rod smaller still in this case.

BTW, Stefan was an S4 audible signal - CW would have been a bit difficult due to the bursts of noise from DCF39, but a QSO would certainly be possible, especially if a quieter frequency were chosen.

Cheers, Jim Moritz
73 de M0BMU

Attachment: dk7fc_ferrite.jpg
Description: JPEG image

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