Dear Stefan, Alan, LF,

 

possibly the signal from Alpha Novosibirsk (4782 km east of here) on 11.9 kHz could provide a hint for transatlantic VLF propagation across a similar range. The attached sketch qualitatively shows a "winged-W" diurnal behaviour of fieldstrength, based on several days of observations near the March equinox:
http://df6nm.bplaced.net/VLF/Alpha/Alpha_levels.png,
http://df6nm.bplaced.net/VLF/Alpha/Alpha_levels_3days.png

 

As expected, attenuation is generally lowest and relatively constant over a six hour period when the whole path is in darkness. After  sunrise at the transmitter at the eastern end of the path, the level began to decrease gradually, until a 15 dB minimum was reached shortly before sunrise at the receiver. Thereafter, daytime fieldstrength across the fully lit path followed solar elevation, with an increase of about 5 dB during the midday maximum. After sunset at the transmitter, a second minimum occured, followed by a build-up until the path has become fully dark again.

To estimate SNR, I have also attempted to plot a crude approximation of diurnal noise levels, as seen here on 9 kHz aftere noise blanking. The range of variation is usually some 5 to 10 dB, with a minimum around 8 h local time. Of course we see a lot of day to day variation in the lightning activity.

 

Thus best SNR would be expected during the six hours of common darkness, and additionally for a couple of daytime hours after the morning noise minimum.

 

I'm no sure about how much an all-water TA route would be different from the Russian overland path. The surface reflections in "multihop" modes will generally benefit from conductivity and smoothness, but the difference should be less pronounced at VLF. Regarding noise, the QRN pattern might be delayed or differently shaped on the east coast of a continent, because lightning activity tends to be higher over land masses. Continuous stateside VLF noise observations or grabbers could provide valuable input.

 

Best 73,
Markus (DF6NM)

-----Ursprüngliche Mitteilung-----
Von: Stefan Schäfer <[email protected]>
An: [email protected]
Verschickt: Do., 8. Jul. 2010, 14:23
Thema: VLF: TA DX on the dreamers band?