29 Jan 2014

PA1SDB on VLF

PA1ASB has been active recently on VLF and on his site he has a grabber showing what signals he has/is copying around 8.270kHz  which is the new favoured spot. This is below 8.3kHz and so falls in the unallocated part of the spectrum as 8.970kHz is now within the  spectrum reserved for sferics research.  Most amateur VLF TX stations are now operating around 8.270kHz. Here in the UK I believe it is legal for ANYONE to TX below 8.300kHz  as long as no harmful interference is caused to allocated services above 8.300kHz. This is my view, not a legal statement. I have asked OFCOM to clarify.

Also of note on these pages are the .SDR configuration files for Spectrum Lab software. It is ESSENTIAL to use Spectrun Lab or very similar software to detect anything at any range. See http://www.qsl.net/pa1sdb/index.htm . I suggest that, if you want to build a VLF amateur RX, to base your configuration files on those given on these pages.

My own experience is that 420uHz or less bandwidth is essential to see any trace of amateur VLF signals integrated over many hours. 42uHz is better. In both cases you have to lock to a VLF MSK signal, Russian Alpha beacons or GPS for excellent stability. This is all sorted out with the .SDR file automatically. You may be surprised  how stable a RX you can make very simply.


at 13:05
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3 comments:

Anonymous said...

The Omega Chain was shutdown September 30 1997, still envious of the 1200' masts but too big for my garden and then there are the people next door to consider.....

The Omega details on the web are interesting, very reliable aviation grade world wide coverage with 10Kw Tx's and very good antennae - all govt paid for, but a bit too expensive after GPS came along when Omega could only do around 2KM accuracy. There are some details on www.jproc.ca about various nav systems.

The lightning detectors are very broadband and very deaf because they are looking for short but very loud impulses, Some home detectors sense direction with crossed rod antennae and use amplitude as a crude distance indicator, others use time of arrival compared to GPS 1PPS then networked back to a server e.g. www.blitzortung.org which is an amateur network. So unless you are very close to a detector a ham Tx should not be much of an issue. I would hope that providing you don't set up next to a govt observer -and there are not many- there won't be much hassle.

I would think that a home detector is not licensed and would be an unprotected service. A very long mark would perhaps only be detected on key up. As the target for detectors has around 20,000A of antenna current into a mile or many long antennae in the sky, a few amps in a few M long wire is not quite the same signal level!!!!!!

Very glad that you are getting back to your Radio Active self Roger.

73's Alan
G8LCO

Wed Jan 29, 06:31:00 pm GMT
Roger G3XBM said...

Alan - for Omega read Alpha beacons. These are usually around still. The MSK signals are, in my view, perfect. You ABSOLUTELY need excellent frequency stability. "Been there, done that". I have changed the text to say Alpha not Omega, my mistake.

Wed Jan 29, 08:14:00 pm GMT
Peter, PA1SDB said...

Hi Roger, Good info ! I use now a GPS with a 1 PPS output. It improves the RX stability a lot.

Thu Jan 30, 06:49:00 am GMT

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