Markus, Appreciate the test, your 100mW sure is QRO for this mode :-) How low can you go? Conditions
earlier when you and Stefan transmitted in QRSS60 were at lest 10db
worse than yesterday, there is also increased QRN as we expect some
showers in the morning.
Unfortunately I couldn't tune the YO window to your Tx frequency as
it was a bit outside the FFT window, adjusted now. it will be
interesting to see the result there and maybe better understand if the
setup as it is today is usable for this slow mode.
Hope Warren, Jay, John and maybe others will join in soon. Thanks for another interesting evening! 73s Chris On Fri, Sep 2, 2011 at 12:13 AM, Markus Vester <[email protected]> wrote:
Hi Chris,
thanks for this! The Saudi Loran traces (GRI 8830)
look very accurate on your 4X grabber. I will try to appear there tonight, and
have started to send a straight carrier on 137780.30. TX power is now
reduced to about 100 mW EMRP.
Best 73,
Markus
Sent: Thursday, September 01, 2011 1:34 PM
Subject: Re: Microhertzing at LF:
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.jpgThe
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 <[email protected]>
wrote:
Dear LF,
(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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