New German amateur test on 8.87kHz planned

Stefan DK7FC is hoping to do a second test transmission on March 15th on 8.97kHz using a vertical antenna, new large loading coil and variometer. Transmissions should start around 1400z. Several stations will be listening and the DF6NM 8.97kHz grabber will be active. Stations possibly within range are DF8ZR (16kms) and  DD7PC (53kms).

8.97kHz does look like the new frontier!

8.97kHz VLF grabber on-line in Germany

DF6NM in Nuernberg, who has been successfully experimenting with sub-9kHz communications now has a temporary grabber on-air to capture any amateur signals on 8.97kHz.  See http://www.mydarc.de/df6nm/vlf/vlfgrabber.htm

Sub-9kHz induction comms resource

John F5VLF/G3PAI has brought a very useful website about induction mode communications below 9kHz to my attention. This site is mainly about cave location and beaconing systems, but there are some neat schematics for local coverage (thousands of feet range) TX and RX circuits that would be suitable for QRSS and similar experiments in the "Dreamers Band" as some have called it. See http://radiolocation.tripod.com/

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.

Amateur DXing below 9kHz (VLF)

Some recent discussion on the LF Reflector is suggesting that distances of >100kms should be workable with amateur stations below 9kHz, albeit running QRO exciters. This would be possible with optimised stations and antennas and very slow QRSS modes. As an example, see the email posted this evening by RA9MB:

I was wonder if it is posible to use a loop on 9 kHz. Serious problem to radiate 9 kHz is high voltage we saw. Loop has that advantage that voltage is not too high. Then i do some estimations. Let's assume vertical loop 15m x 50 m with 20 mm diameter coper tube as a wire. Then effectivity of such a loop on 9 kHz is about -65 dB. It is adequate to radiate 1 mW
on 9kHz (I=250A, TX power about 4 kW). We saw such a radiation should give abt 100 km  distance in QRSS. Besides such a loop is well suited for 136 kHz. On 136 kHz it effectivity should be about -25 dB. Not too bad: 1 W radiation with 400 W TX :-)

NoV permits for operation below 9kHz

OFCOM has informed me today that, subject to acceptable outcomes of consultation with other sub-9kHz spectrum users such as the Met Office, they will consider issuing NoVs (similar to those issued for 501-504kHz) to existing UK radio amateurs to permit operation at frequencies below 9kHz. Any such operation would be on a non-interference basis.  Application forms should be submitted to Rod Wilkinson at OFCOM (with as much detail as possible) using the NoV form available at http://www.ofcom.org.uk/radiocomms/ifi/licensing/classes/amateur/applications/ofw306.pdf

UK permits for transmissions below 9kHz?

There has been some debate today on the RSGB's LF Reflector about how legal amateur transmissions in the UK would be at frequencies below 9kHz. Apparently the old Radio Communication Agency failed to come back with an answer to a request around 2000-2001. We're wondering what OFCOM would say today, so I've emailed them to ask. They have already replied and told me the query is being forwarded to their Spectrum Management Team and they are considering their answer over the next few weeks.

Communication over any distance at frequencies below 9kHz is a real challenge and the modes used are usually conduction through the earth or sea (so called "earth mode") or by induction. Very little power is radiated unless enormous powers are used e.g. in the USA's Project Sanguine when megawatts were used at 76Hz to communicate worldwide with submerged submarines. Distances much beyond 10kms are highly unlikely with amateur powers and systems.