Re: LF: EbNaut March 30/31

[Markus Vester <markusvester@aol.com>]

Well done Domenico and Rob, that should probably be a new distance record for LF EbNaut.

The improved time offset was surely just serendipity on my side, as I normally don't even care to calculate the starttime to better than 0.1 s. But it is surprising how very minor start time differences sometimes seem to produce significant and unpredictable differences in EbN0. I suspect that the decoder is assigning samples to symbols without interpolation (i.e. nearest-neighbour), so that pushing just one noisy sample over a symbol boundary might have an unexpectedly large effect.

Best 73,
Markus (DF6NM)  


-----Ursprüngliche Mitteilung-----
Von: Domenico IZ7SLZ <iz7slz.domenico@gmail.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Sa, 31. Mrz 2018 18:10
Betreff: Re: LF: EbNaut March 30/31

Hello Markus, Riccardo  and all,

all last Riccardo's EbNaut transmissions have been copied here in JN80nu (QRB 630 km) by the 'autodecode' program (log attached).

Thanks to your today's report Markus, i have noted the time offset (about +0.005 s) to apply at the recordings  in order to decode Rob K3RWR (QRB 7612 km) and i found only one decode at 03.00 UT of 31-03-2018 !

Very very weak signal as shown in the attached plot.

phase   0    0    0    0    0
carrier phase: -4.1 deg
carrier Eb/N0: -0.4 dB
carrier Es/N0: -11.31 dB
carrier S/N: 17.93 dB in 595.2 uHz, -14.32 dB in 1Hz, -48.30 dB in 2.5kHz
elapsed 75
found rank 4467 ber 3.4762e-01 Eb/N0 -0.2 M -1.222081757e+01 ph 0 0,0,0,0 [K3RWR_FM18QI]

Setup used here: miniwhip antenna, JRC NRD-92N receiver, 10 MHz reference oscillator with GPS NEO-8 and Program 'vlfrx-tools'. I made several attempts to improve the report by changing -a and -t parameters of 'vtblank' but this seems to be the best report.

Many thanks for to Rob and Riccardo for the signals and to Paul Nicholson for FB vlfrx-tools.

73 and best wishes for Easter !

Domenico, IZ7SLZ  

Thanks to 

On 31 March 2018 at 14:00, Markus Vester <markusvester@aol.com> wrote:

Again a strong signal with some error-free decodes from IW4DXW. Also found K3RWR finally on 137490 Hz, but only once after 4:00, and another near-miss around sunrise after 4:30 (logs attached).

Rethinking my frequency suggestion, it may not be ideal to place simultaneous signals from both sides of the pond so near to each other. EbNaut employs hard-keyed phase switching both for the transmitter and for the matched filter in the receive software, so keying sidebands or aliasing from a near station may spill over an adjacent weak signal (although in principle this could be minimized by orthogonal modulation, using identical symbol timing for all stations, and frequencies spaced by an exact integer multiple of the common clockrate). But there are also other disadvantages, like noise-blanker induced crossmodulation and threshold increase. So in the end it may be better to use either separate timeslots or separate subbands, in analogy to our TA- and Eu-QRSS slots.

Best 73,
Markus (DF6NM)


-----Ursprüngliche Mitteilung-----
Von: Markus Vester <markusvester@aol.com>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Verschickt: Fr, 30. Mrz 2018 23:03
Betreff: LF: EbNaut March 29/30

Last night Mar 29/30, I got excellent decodes from IW4DXW, but unfortunately not a single one from K3RWR on 137490 Hz.

Best 73,
Markus (DF6NM)
______________________________________
LF: EbNaut attempt at 137495 kHz 
Von: Riccardo Zoli <riccardozoli80@gmail.com>
An: LF Group <rsgb_lf_group@blacksheep.org>
Datum: Do, 29. Mrz 2018 19:53

Hi LF

This night, I have scheduled some transmissions every hour (start at xx:00).

QRG: 137494.99988
8K19A
CRC 20
3 sec./sym.
6 char
duration: 29 min. 36 sec.

Reports are welcome.

All the best

73 de Riccardo IW4DXW
______________________________________
Re: LF: K3RWR LF EbNaut Trial #2 
Von: Rob Renoud <k3rwr@md.metrocast.net>
An: rsgb_lf_group <rsgb_lf_group@blacksheep.org>
Datum: Do, 29. Mrz 2018 21:22

TU all for LF EbNaut reception reports for my 28/29 March 2018 trial of a 12 char, CRC 15, 2 sec symbol 8K19 transmission.  The first night results of this format are very positive!

I will transmit this format again this evening (29/30 Mar) and tomorrow (30/31 Mar) on frequency 137.490 KHz.

Reports and comments welcome.   Work is starting this weekend on EbNaut RX capability for my station.

73,
Rob - K3RWR