Sub-9kHz Induction Field DX?

With all the discussion recently on the LF Reflector about how to radiate a signal on sub-9kHz I'm left wondrering how far, practically, one could expect to get simply with sub-9kHz electromagnetic induction using multi-turn loops at each end.

It's quite easy for anyone to generate 50-100W or so and feed this into a largish diameter multi-turn loop. Correctly aligned and with a similar loop at the far end and using decent weak signal processing just what range might be possible using modes like QRSS or WSPR? Has anyone tried this to see just what is practical, simply using induction fields?

The Cave Radio Group (CREG) may have some answers but I'm not a subscriber so can't read any of their documents.

LATER: Jim Moritz M0BMU did some sums (see my webpage on sub-9kHz radio) and reckons that about 4.4kms is the best one could do with 100W and a 10m diameter loop and purely inductive communications. More power and bigger (low loss) loops could get a bit further still.

9kHz band receiver front-end (M0BMU)

Jim M0BMU has produced a neat loop/preamp design suitable for listening on the 9kHz band for which we hope NoVs will be available shortly in the UK. His design has sufficiently low noise to provide a state-of-the-art receiver for this band when used with the many excellent software based VLF receivers such as Winrad and Spectrum Lab. This circuit was posted on the LF Reflector this evening.

New African WSPR beacon coming

After successfully deploying the V53ARC WSPR beacon in October, OE1FM will have a second beacon system running in two weeks. 5X7JD (Uganda) has agreed to host a 1W WSPR beacon system at his Masaka QTH. See: www.oe1ifm.at

Whistlers!

This evening the VLF natural noise receiver in Todmorden, UK is buzzing with whistlers in addition to the almost continuous stream of tweeks. Whistlers are audible frequency descending tones caused by the dispersion of a lightning triggered impulse as it travels along magnetic field lines. At the moment I'm hearing about one whistler every 2 minutes.

Want a bigger 28MHz antenna?

Nick G4IKZ has just sent me this link to G0SXC's QRZ.com page showing his massive yagi for 28MHz. It has a boom length of 78 feet and a gain of 13.1dBd. Remember that each element is about 16 feet long, so you get an idea what a monster this is. I bet his neighbours must love him! This also explains why Kevin is such a consistent signal in East Anglia some 200 miles away.

10m tropo reception

Been on 10m this morning using WSPR at 2W. During the last hour  the 5W signal of G3JKV near Dorking has been received several times at a distance of 123kms. Although there's some aircraft scatter visible on the signal, I think this is mainly tropo propagation.

Sub-9kHz NoV application and German VLF tests

Later this week I hope to submit my application to OFCOM for a special research permit (NoV) to test at VLF frequencies below 9kHz. Things are moving on at a pace in Germany with several stations gearing up to carry out some serious radiated tests (i.e. not by induction or conduction) and some new DX records below 9kHz are expected to be set. There is a lot of  discussion on the LF reflector about antennas, loading coils, loops and elevated loops using grounded electrode pairs. See also my webpage on this at http://sites.google.com/site/g3xbmqrp/Home/10khz

814kms on 500kHz with 500uW, a 10m halo and 5m of coax

This evening my 500kHz QRP WSPR signal managed to reach DL3NDR despite the antenna system being "downgraded" yesterday: the spiral top hat has gone and in its place is the 28MHz halo with 5m coax feeder. ERP is I believe some 6dB lower at around 500uW, yet it still gets this far.

New amateur DX record below 9kHz (VLF) - 12.1kms

Markus DF6NM has reported on the LF Reflector that he's been able to receive his test transmissions on 8.97kHz at a distance of 12.1kms. See http://www.mydarc.de/df6nm/vlf/vlf_12km.jpg. He has calculated his ERP at 1.3uW into his relatively small antenna with 1.4 Henry loading coil. The TX was a 35W car-radio audio amplifier. His RX antenna was 6m long and he used SpecLab with very narrow effective bandwidth. There are several others now experimenting below 9kHz, so this new record may not last long, especially as Marcus was using relatively low TX power. OFCOM is considering the issue of NoVs for <9kHz in the UK.

More 500kHz tests tonight

This evening I'll be running the 500kHz WSPR beacon into the 10m halo and its feeder again via the ferrite rod. Last night the best DX was to Holland. ERP is probably around 500uW.