Date: Fri, 12 Apr 2019 10:11:06 +0200 (CEST)
From: Jacek Lipkowski <sq5bpf@lipkowski.org>
To: rsgb_lf_group@blacksheep.org
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Subject: Re: ULF: EbNaut message transmitted from ground loop
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On Thu, 11 Apr 2019, DK7FC wrote:

> That's great! Amazing! 976 km distance in the ULF range!
> A decode at 15.63 dB carrier S/N.

Improved parameters:

sq5bpf@jitter:/stuff2/sq5bpf/vlf_stefan2$  vtcat -p < stefan_2970_1  | vtfilter -a th=4 -h bp,f=2970,w=2300 > pliktmp7

sq5bpf@jitter:/stuff2/sq5bpf/vlf_stefan2$ vtblank -v  -d0.0007 -a22 -t 70 < pliktmp7 |  vtmult -f 2970.1 | vtresample -r 240 |    vtresample -r 10  |vtraw -oa  | ebnaut  -dp16K21A -r10 -c2 -v -k16 -S6 -N7  -PS -L 50000


vtblank: selected channel: 1 = -:1
vtblank: channels: 1, sample_rate: 48000
vtblank: hfactor: 0.000e+00
vtblank: afactor: 22.000
initial reference phase 88.1 amplitude 8.289e-04
phase   0    0    0    0    0
vtblank: end of input
vtblank: dropsum 0 50041841, nfp 359999999
vtblank: dropfactor 0 1.390e-01
phase   1  180  180  180  180
found rank 6348 ber 4.2147e-01 Eb/N0 -2.0 M -2.316530794e-02 ph 1 
180,180,180,180 [DK7FC/P]
carrier phase: -10.7 deg
carrier Eb/N0: -0.3 dB
carrier Es/N0: -15.26 dB
carrier S/N: 15.70 dB in 133.5 uHz, -23.04 dB in 1Hz, -57.02 dB in 2.5kHz
elapsed 98
phase   2   30   30   30   30

I'm still trying to find better decoding parameters. For now i'm trying 
a bandpass filter with varying widths, and trying to find the best 
noiseblanker parameters for each of these filters. A 2300Hz filter 
seems best for now. I'm trying different bandwidths in 100Hz increments, 
started at 1800Hz, currently i'm trying 2500Hz and 2600Hz, about 840 
different vtblank parameters are tried per each bandwidth. Later i will 
repeat the tests with different th parameter, preset notches in the 
passband etc.

Unfortunately the search is done on two workstations with i7-7700 (8 
cores) at 4GHz (this is due to intel turbo-boost, these are 3.6GHz cpus). 
I will try to set up a proper htcondor cluster later with more machines.

> Can you describe your RX antenna and location/position of it?

This is an e-field antenna: BF862 amplifier, the e-probe is a big can 
(probably around 20cm height, 13cm diameter). The antenna is located on 
the roof of a 4-story building in Warsaw. Care was taken to use the best 
engineering practices (zip-ties, duct tape etc).

The antenna location is bad, but i've tried not to add more noise than it 
already has by eliminating ground loops, isolating from noisy power 
supplies etc.

> Thank you for your work!  I will try to use your parameters and then we see 
> the digital loss of the vorbis path.
> It is a good set of data to 'play' with, because this distance/frequency/mode 
> has never been done by radio amateurs before.

I can make the raw data avaliable in case anyone is interested.

> A first detection/decode DL > SP.
>
> Eventually i'll do more experiments this weekend. Let's hope for a suitable 
> wx. The last days have not been really quiet ;-)
>
> And BTW, when is your next transmission together with Marcin?

There is no time set yet. I need to finish my tx first.

> Another thing: Sometimes i git better results when using vtfilter -h lp... -h 
> hp... instead of vtfilter -h bp... because the edges are a bit smoother. Also 
> it can improve the SNR to place the center frequency of the filter not to the 
> TX frequ ency but some 100 Hz up or down, depending on the noise 
> distribution.

I've tried the hp/lp combination but usually it wasn't better.

What works is to look at the spectrogram and notch out the noise peaks in 
the filter passband.

> PS: I remember you asked a few times if i can go lower than 5170 Hz. Now we 
> are there :-)

Yes! But don't stop until you get to DC :)

VY 73

Jacek / SQ5BPF