Dear Sub-9kHz'ers,

 

Marco DD7PC just made me aware of new German regulations, which also includes a change of the unallocated VLF range. The latest version of the "Freqenzverordnung" (FreqV)
http://www.gesetze-im-internet.de/bundesrecht/freqv/gesamt.pdf
has become effective already on August 27, 2013, and includes an allocation of 8.3 to 9 kHz to the passive weather observing service (ie. lightning locator networks). Strictly speaking, this would make 8.97 kHz transmissions illegal in Germany (although there may be a loophole with national footnote 2 regarding "Induktionsfunkanlagen"). If I recall right, a similar legal change in the UK had been announced in this group some time ago, leading to the installation of some grabber windows around 8.27 kHz.

 

In practice, radiated powers achievable by amateurs (milliwatts at best) are ten orders of magnitudes below to that emitted by lightning events (100 megawatts). The chance of amateur interference to a broadband lightning locator would thus be absolutely neglegible. Even if somebody happened to activate his kite within one kilometer from a detector station, any further effect of interference would still be suppressed by redundancy in the lightning location network.

 

Still, for publicly visible work (like claiming first contacts etc), we should consider moving below 8.3 kHz. Of course there are disadvantages, like
- local interference eg. from railway lines seems to be much denser and stronger at lower frequency,
- at same antenna voltage, radiated power will be 1.4 dB less,
- more coil winding is required,
- acoustical side-effect of transmitting may be more disturbing,
... es nervt einfach!!

 

But then, one should always embrace change... positive aspects may be
- lower QRN background in quiet locations,
- with common international legislation, the necessity of sub-9kHz NOV's in the UK might become obsolescent,
- EA5HVK might be motivated to provide an Opera version with flexible frequency assignment.

 

In my location, I am mostly affected by 16.67 / 33.3 Hz modulated interference emitted by railway overhead lines, in addition to the usual 50 Hz related junk. To possibly identify a sweet spot with relatively low interference, I have temporarily shifted the frequency range of my faster VLF grabber windows:
http://df6nm.darc.de/vlf/vlfgrabber.htm
Judging by the first hours, near 8280 Hz may be significantly better than 8270. But interference comes and goes with time, so longer observations are needed. Note that the heavy interference between 11 and 12 UT could have been exacerbated by my noise blanker settings as it is much less severe in the wideband window. At this time, I would like to encourage other receiver operators to closely investigate their noise levels just below 8.3 kHz.
 
Best 73,
Markus (DF6NM)