on finding a good 11.8km location and extracting the signal from
sferics and other noise, and very good SNR at 3.8 mHz at 11.8 km, 1570
your Thursday (June 2nd) early-morning message you mentioned
that noise was higher on the H-field receiver, and that (SNR_E / SNR_H)
was ~ 15 dB.
you perhaps remember roughly how much higher measured H noise was (how
much higher than measured E noise)?
reason for the question is: an experimental estimate of
(signal_E/signal_H) would be quite interesting at this frequency and
range; it could be a helpful indicator of propagation effects.
your H noise was ~ 14 dB above your E noise (early-morning of June 2nd),
that would seem to agree with a standard algebraic approximation of:
11.8 km 1570 Hz non-radial signal_E/signal_H = 29.3 dB (excluding
so that would be interesting, because I would not expect
(signal_E/signal_H) to be very close to the theoretical value at 11.8
km 1570 Hz, but this could be good news if it indicates that some
aspects of propagation are not too far from normal.
you recall roughly how high H noise was, compared to E noise?
...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...
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
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!