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Date: Thu, 1 Sep 2011 13:34:50 +0200
Message-ID: <CAK59VFPYTZ6YVQeP6Eic4ozygHEivt+F9S3DegeuAzTNniU0Lg@mail.gmail.com>
From: Chris 4X1RF <chrisgomy@gmail.com>
To: rsgb_lf_group@blacksheep.org
Subject: Re: Microhertzing at LF:
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Markus, LF,

As a newcomer to LF I find this as an interesting experiment for real low
power or long distance tests for those who can achieve the necessary
frequency stability requirements. I found this to be quite a challenge...

I have followed your initiative and started similar windows on my grabbers
in YO: http://dl.dropbox.com/u/10280270/YO/TA3600.jpg and 4X:
http://dl.dropbox.com/u/10280270/4X/TA3600.jpg

The 4X grabber is currently using the Mercury HPSDR receiver (
http://openhpsdr.org) which is GPSDO locked. However, the audio is routed to
SpectrumLab using Virtual Audio Cable as a virtual sound card. I have no
info regarding VAC sample rate accuracy or how I can automatically adjust it
so this may be a limiting factor, further experimentation is needed. In the
worst case, a real sound card could be used but then it also has to be
locked to GPS.

The YO grabber is usually using GQD as a reference for the sound card sample
rate calibration in SpectrumLab and the LF receiver is based on a laboratory
grade VTCXO. GQD being off air, I was forced to use DHO which is not very
reliable during the night for me as can be seen on the 137.775 Loran line.

Thanks for the challenge!


73s
Chris 4X1RF






On Wed, Aug 31, 2011 at 8:05 PM, Markus Vester <markusvester@aol.com> wrote:

> Dear LF,
>
> inspired by the very fruitful narrowband weak-signal detections on VLF, I
> have set up a temporary LF spectrogram, using Rubidium locked oscillators
> and a 0.438 mHz FFT bandwidth
>  http://www.alice-dsl.net/df6nm/grabber/TAnarrow.jpg
> (updated every two hours).
>
> Frequency:
> The receive band is currently 7 Hz wide around 137777.5 Hz, within which
> the visible display slots can be shifted around a posteriori on request. At
> the moment I'm showing two slots around European Loran lines
>  137778.3705 Hz (GRI 7499 from Sylt and Lessay),
>  137775.0000 (GRI 8000 from Slonim and Simferopol).
> I chose the TA slot for the availability of other grabbers, but maybe a
> dedicated ultra-narrowband slot (eg. 10 MHz/73 = 136986.301 Hz) would be a
> better option - suggestions welcome!
>
> Sensitivity:
> Compared to my own 21 mHz TA grabber, the bandwidth reduction should
> provide a 17 dB reduction of noise, or 11 dB versus Argo-120 at 5.3 mHz. Of
> course you will need to transmit a much longer dash (eg. one hour instead of
> one minute) with good frequency stability. A GPS- or Rubidium-derived
> carrier would be the best option, but a good 1e-9 class OCXO would work just
> as well.
>
> Groundwave:
> In quiet daytime conditions, a radiated power of only 10 nanowatts should
> be able produce 10 dB SNR. This could be achieved by sending 5.5 mA up a
> whip at 1 m effective height! Or perhaps even from Lubos' ferrite antenna in
> TX mode?
>
> Skywave:
> During a few nights in Februrary 2006, John W1TAG transmitted GPS
> controlled straight and 15-minute phase-cycled carriers. Receptions in
> Europe by G3PLX and myself revealed long periods of stable skywaves, well
> suited for sub-millihertz analysis. Some details and spectrograms can be
> found in
> http://df6nm.bplaced.net/LF/slow_psk/
>
> Now I hope to see some really feeble signals soon...
>
> Best 73,
> Markus (DF6NM)
>
>
>
>
>

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<div dir=3D"ltr">Markus, LF,<br><br>As a newcomer to LF I find this as an i=
nteresting experiment for real low power or long distance tests for those w=
ho can achieve the necessary frequency stability requirements. I found this=
 to be quite a challenge...<br>
<br>I have followed your initiative and started similar windows on my grabb=
ers in YO: <a href=3D"http://dl.dropbox.com/u/10280270/YO/TA3600.jpg">http:=
//dl.dropbox.com/u/10280270/YO/TA3600.jpg</a> and 4X: <a href=3D"http://dl.=
dropbox.com/u/10280270/4X/TA3600.jpg">http://dl.dropbox.com/u/10280270/4X/T=
A3600.jpg</a><br>
<br>The 4X grabber is currently using the Mercury HPSDR receiver (<a href=
=3D"http://openhpsdr.org">http://openhpsdr.org</a>) which is GPSDO locked. =
However, the audio is routed to SpectrumLab using Virtual Audio Cable as a =
virtual sound card. I have no info regarding VAC sample rate accuracy or ho=
w I can automatically adjust it so this may be a limiting factor, further e=
xperimentation is needed. In the worst case, a real sound card could be use=
d but then it also has to be locked to GPS.<br>
<br>The YO grabber is usually using GQD as a reference for the sound card s=
ample rate calibration in SpectrumLab and the LF receiver is based on a lab=
oratory grade VTCXO. GQD being off air, I was forced to use DHO which is no=
t very reliable during the night for me as can be seen on the 137.775 Loran=
 line.<br>
<br>Thanks for the challenge!<br><br><br>73s<br>Chris 4X1RF<br><br><br><br>=
=A0 <br><br><br><div class=3D"gmail_quote">On Wed, Aug 31, 2011 at 8:05 PM,=
 Markus Vester <span dir=3D"ltr">&lt;<a href=3D"mailto:markusvester@aol.com=
">markusvester@aol.com</a>&gt;</span> wrote:<br>
<blockquote class=3D"gmail_quote" style=3D"margin: 0pt 0pt 0pt 0.8ex; borde=
r-left: 1px solid rgb(204, 204, 204); padding-left: 1ex;"><font color=3D"bl=
ack" face=3D"arial" size=3D"2">
<div>Dear LF,</div>


<div>=A0</div>


<div>inspired by the very fruitful narrowband weak-signal detections on VLF=
, I have set up a temporary LF spectrogram, using Rubidium locked oscillato=
rs and a 0.438 mHz FFT bandwidth <br>
=A0<a href=3D"http://www.alice-dsl.net/df6nm/grabber/TAnarrow.jpg" target=
=3D"_blank">http://www.alice-dsl.net/df6nm/grabber/TAnarrow.jpg</a></div>


<div>(updated every two hours).</div>


<div>=A0</div>


<div>Frequency:<br>
The receive band is currently 7 Hz wide around 137777.5 Hz, within which th=
e visible display slots can be shifted around a posteriori on request. At t=
he moment I&#39;m showing two slots around European Loran lines<br>
=A0137778.3705 Hz (GRI 7499 from Sylt and Lessay),<br>
=A0137775.0000 (GRI 8000 from Slonim and Simferopol).<br>
I chose the TA slot for the availability of other grabbers, but maybe a ded=
icated ultra-narrowband slot (eg. 10 MHz/73 =3D 136986.301 Hz) would be a b=
etter option - suggestions welcome!</div>


<div>=A0</div>


<div>Sensitivity:<br>
Compared to my own 21 mHz TA grabber, the bandwidth reduction should provid=
e a 17 dB reduction of noise, or 11 dB versus Argo-120 at 5.3 mHz. Of cours=
e you will need to transmit a much longer dash (eg. one hour instead of one=
 minute) with good frequency stability. A GPS- or Rubidium-derived carrier =
would be the best option, but a good 1e-9 class OCXO would work just as wel=
l.</div>



<div>=A0</div>


<div>Groundwave:<br>
In quiet daytime conditions, a radiated power of only 10 nanowatts should b=
e able produce 10 dB SNR. This could be achieved by sending 5.5 mA up a whi=
p at 1 m effective height! Or perhaps even from Lubos&#39; ferrite antenna =
in TX mode?</div>



<div>=A0</div>


<div>Skywave:<br>
During a few nights in Februrary 2006, John W1TAG transmitted GPS controlle=
d straight and 15-minute phase-cycled carriers. Receptions in Europe by G3P=
LX and myself revealed long periods of stable skywaves, well suited for sub=
-millihertz analysis. Some details and spectrograms can be found in <br>

<a href=3D"http://df6nm.bplaced.net/LF/slow_psk/" target=3D"_blank">http://=
df6nm.bplaced.net/LF/slow_psk/</a></div>


<div>=A0</div>


<div>Now I hope to see some really feeble signals soon...</div>


<div>=A0</div>


<div>Best 73,<br>
Markus (DF6NM)</div>


<div><br>
<br>
<br>
=A0</div>


<div style=3D"clear: both;"></div>
</font></blockquote></div><br></div>

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