...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
|
11km_3.8.png
Description: PNG image
11km_424.png
Description: PNG image
11km_wide.jpg
Description: JPEG image
|
