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Date: Thu, 05 Oct 2017 14:00:35 +0200
From: DK7FC <selberdenken@posteo.de>
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To: rsgb_lf_group@blacksheep.org
References: <15ec7c794b3-bff-66@webjas-vac136.srv.aolmail.net> <alpine.DEB.2.11.1710022138560.734@mailn.lipkowski.org> <59D2BD65.4080909@posteo.de> <59D4B109.27652.1415B4FA@mike.dennison.ntlworld.com> <7737095b-edc9-8b5f-ebf5-2a6b2884d425@abelian.org> <alpine.DEB.2.11.1710050933380.734@mailn.lipkowski.org>
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Subject: Re: VLF: 300 mA on 6470 Hz
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Hi Jacek, VLF,

First, let me change something in the next transmit announcement. It 
could make sense to start an hour earlier because the sunrise will be 
earlier near Moscow. Here, the QRN starts to rise at arround 16 UTC as 
well, so the band seems to open towards the east then. Also it makes 
sense to switch to 16K21A. I think Alex has 8 GB RAM so he must have a 
64 bit PC, so it should work to decode 16 chars at 16K21A. It should be 
better for you as well, regarding timing and code efficiency. Paul will 
have no problem anyway :-)

*f = 6470.100000 Hz
Start time: 05.October.2017  16:00:00 UTC (daily)
Symbol period: 20 s
Characters: 16
CRC bits: 19
Coding 16K21A
Duration: 12h
Antenna current: 300 mA*

About QSY, a good idea.
Recently i had the idea to transmit 2 messages simultaneously, on 
slightly different frequencies. But we could also try +- 40 Hz apart 
from the resonance frequency.
Since i have a linear PA, it should work. It should even work to hold 
the phase and antenna current for each individual signal (for example 
when it starts to rain).
Since my VLF coil is relatively compact for the 1.3 H, it uses a thin 
wire (0.25 mm) and has a relatively low Q. This causes more losses but 
on the other side it is more broadbandish. So it should work to transmit 
on 6430 and 6510 Hz to the same time. I would need to reduce the antenna 
current to 70% on each frequency of course.
We could try EbNaut with the same parameter settings on both 
frequencies. Or we can try a simple carrier. However EbNaut is more 
interesting i find. It could be interesting to create an error map from 
both transmissions and look where differences between them can be found 
(XOR).
I would then use a 16K mode, so we get more symbols that can differ.
On the RX side, the noise blanker will affect both frequencies in the 
same way i think. But local QRM near the different transmit frequencies 
may have the worst effect that influence the comparison.
The 1 character message was strong enough on your side to decode even if 
it would be 3 dB weaker.
A lot of stuff on the list to do...

73, Stefan

Am 05.10.2017 09:40, schrieb Jacek Lipkowski:
> maybe Stefan could qsy a bit?
>
> for example i'm 19.8 wavelengths from Stefan (and Paul is almost the 
> same). shifting 81 Hz either way would make the path 1/4 wavelength 
> longer/shorter. if there are some multipath propagation effects then i 
> should get a stronger, or weaker signal. the offset should be the 
> average of offsets that would lead to a 1/4 wavelength path difference 
> for all stations that currently receive Stefan.
>
> VY 73
>
> Jacek / SQ5BPF

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Hi Jacek, VLF,<br>
<br>
First, let me change something in the next transmit announcement. It
could make sense to start an hour earlier because the sunrise will be
earlier near Moscow. Here, the QRN starts to rise at arround 16 UTC as
well, so the band seems to open towards the east then. Also it makes
sense to switch to 16K21A. I think Alex has 8 GB RAM so he must have a
64 bit PC, so it should work to decode 16 chars at 16K21A. It should be
better for you as well, regarding timing and code efficiency. Paul will
have no problem anyway :-)<br>
<br>
<b>f = 6470.100000 Hz<br>
Start time: 05.October.2017&nbsp; 16:00:00 UTC (daily)<br>
Symbol period: 20 s<br>
Characters: 16<br>
CRC bits: 19<br>
Coding 16K21A<br>
Duration: 12h<br>
Antenna current: 300 mA</b><br>
<br>
About QSY, a good idea. <br>
Recently i had the idea to transmit 2 messages simultaneously, on
slightly different frequencies. But we could also try +- 40 Hz apart
from the resonance frequency.<br>
Since i have a linear PA, it should work. It should even work to hold
the phase and antenna current for each individual signal (for example
when it starts to rain).<br>
Since my VLF coil is relatively compact for the 1.3 H, it uses a thin
wire (0.25 mm) and has a relatively low Q. This causes more losses but
on the other side it is more broadbandish. So it should work to
transmit on 6430 and 6510 Hz to the same time. I would need to reduce
the antenna current to 70% on each frequency of course. <br>
We could try EbNaut with the same parameter settings on both
frequencies. Or we can try a simple carrier. However EbNaut is more
interesting i find. It could be interesting to create an error map from
both transmissions and look where differences between them can be found
(XOR).<br>
I would then use a 16K mode, so we get more symbols that can differ.<br>
On the RX side, the noise blanker will affect both frequencies in the
same way i think. But local QRM near the different transmit frequencies
may have the worst effect that influence the comparison.<br>
The 1 character message was strong enough on your side to decode even
if it would be 3 dB weaker. <br>
A lot of stuff on the list to do...<br>
<br>
73, Stefan<br>
<br>
Am 05.10.2017 09:40, schrieb Jacek Lipkowski:
<blockquote
 cite="mid:alpine.DEB.2.11.1710050933380.734@mailn.lipkowski.org"
 type="cite">maybe Stefan could qsy a bit?
  <br>
  <br>
for example i'm 19.8 wavelengths from Stefan (and Paul is almost the
same). shifting 81 Hz either way would make the path 1/4 wavelength
longer/shorter. if there are some multipath propagation effects then i
should get a stronger, or weaker signal. the offset should be the
average of offsets that would lead to a 1/4 wavelength path difference
for all stations that currently receive Stefan.
  <br>
  <br>
VY 73
  <br>
  <br>
Jacek / SQ5BPF
  <br>
</blockquote>
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