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Re: ULF: A short summer experiment on the 191 km band

To: [email protected]
Subject: Re: ULF: A short summer experiment on the 191 km band
From: DK7FC <[email protected]>
Date: Tue, 05 Jun 2018 00:46:50 +0200
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...and here are some more images, showing spectrograms from the 2 hour long carrier transmission. A spectrogram is more common in the LF world maybe.
Amazing, the carrier reaches 25 dB in 424 uHz. Even in 3.8 mHz ('DFCW-600') it is still 'O copy'. The wideband spectrogram shows how vlfrx tools' filter curves look and how the hum and sferics are removed.

I calculated that the far field begins at just 30.4 km distance on that band. I'm not so far away...

73, Stefan


Am 02.06.2018 12:41, schrieb DK7FC:
Hello dear friends of the Ultra Low Frequencies,

I want to report about a short experiment i've done on thursday morning.

Early in the morning i placed my RX loop antenna (0.8m diameter, 84 turns, preamp) and an active E field antenna (now using a J310) in JN49KK03HQ . That's a distance of 11.8 km to the TX antenna, about 3x farer than the best distance crossed on that frequency so far, but still well into the near field.
For about two hours i transmitted a carrier on 1570.01 Hz followed by an EbNaut message (3 chars, 16K21A, CRC20, 6 sec/symbol). The ERP was just 90 nW.
This time the E field antenna was not sourrounded by trees. Although it was mounted just 2...3 m above the ground, reception in the E field was excellent. A spectrum peak integrating two hours of carrier transmission reaches > 30 dB SNR in 134 uHz, see attachment.

Unfortunately there was a bad contact on the BNC connector of the H field (problems of portable equipment which is built up and down several times | headless recorder, i.e. no chance to check if all works well) , but at least during a part of the EbNaut message it was working, so a comparison of the E and H performance is possible: The E-field SNR is about 15 dB higher than the H-field SNR. This is expected when using an E-field antenna in the near field to receive a signal radiated from an E-field antenna.
But it is not only propagation, it is also the lower hum components in the E field.

Another attachment shows the extraction, filtering and sferic blanking out of the recorded signal as well as the 3 character message decode, E field only.

This experiment was done just for fun, to check the equipment and to spend some hours in the nature :-)
Another one will be done very soon (today?), but then in the far field!

73, Stefan

Attachment: 11km_3.8.png
Description: PNG image

Attachment: 11km_424.png
Description: PNG image

Attachment: 11km_wide.jpg
Description: JPEG image

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