Return to KLUBNL.PL main page

rsgb_lf_group
[Top] [All Lists]

LF: Ghost bands created by VLF ionospheric heating

To: <[email protected]>, <[email protected]>
Subject: LF: Ghost bands created by VLF ionospheric heating
From: "Markus Vester" <[email protected]>
Date: Sun, 10 Feb 2013 01:07:53 +0100
Dkim-signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=mx.aol.com; s=20121107; t=1360454877; bh=dleMwLCq40w8bpjxnfOz4J+vOIgrQnm8sIr4T/XLekc=; h=From:To:Subject:Message-ID:Date:MIME-Version:Content-Type; b=K0LtqoQqEzIQpP+bR7wtBA9zrG6ryAjYVe7LWHUeQ94bPutvfa5oOUH7hd0Bff0PC LlKmlmGgiJMTJyBf7aA3rmpcZiZ0wljT8gkXaAgAPuSqLLvxI3UZKyzIRVMLG+3Vnt qQkASwzSuKc8i82OVm15iQ7dfPEX4I3qaTydCiYY=
Reply-to: [email protected]
Sender: [email protected]
On my LF grabber http://www.df6nm.de/grabber/Grabber.htm there is again a ~ 200 Hz wide red noise band centered on 137.08 kHz. It has been observed several times before but has been absent for a few months. Sometimes it is accompanied by a weaker "brother", centered on 137.18 kHz with purple (ie. northerly) colour. The structure is reminiscent of an MSK signal ("the ghost of CFH"). The bands were seen regularly but are stronger in nights with strong Luxemboug effect. 
 
After a lot of head scratching, a while ago I have found a really astonishing explanation for this effect: It is ionospheric cross modulation, with a pair of strong VLF transmitters acting together as a modulated heater.
 
DHO38 on 23.4 kHz and HWU (which has recently reappeared on 21.75 kHz) have a difference frequency of 1.65 kHz, with the sum of the two FSK shifts. Similar to an AM demodulator, the beat frequency between the two transmitters modulates the electron temperature in the D-layer, and the variable absorption creates crossmodulation on the carriers of HGA22 (135.43 + 1.65 kHz) and DCF39 (138.83 - 1.65 kHz). This constellation is rather unusual not only in that the heating is done by VLF signals. What is even more peculiar is that unlike a simple AM transmitter, the two non-colocated heaters must produce an inhomogeneous and fast moving heating pattern.
 
If you look at the Twente WebSDR http://websdr.ewi.utwente.nl:8901/ now, you can currently see and hear prominent 1.65 kHz FSK sidebands around DCF39 and also DCF49 (128.93 kHz). However HGA seems less affected at Twente, presumably because the easterly reflection area is not so well illuminated for that path.
 
Best 73,
Markus (DF6NM)
 
<Prev in Thread] Current Thread [Next in Thread>