Lowest frequency commercial/military VLF transmissions?

The two lowest VLF frequencies in use are apparently:

• 11.904 kHz  RSDN-20 network, a Russian navigation VLF system with transmitters located in Novosibirsk, Krasnodar, etc
• 82 Hz  ZEVS system, an ELF transmitter located on the Kola peninsula and dedicated to strategic transmissions to Russian nuclear submarines.

Jean-Louis F6AGR receives both stations near Paris with an E-field receiver consisting of a home-brew receiver fitted with a FET/BJT front end and a 1m long cylinder vertical antenna.

Improved VLF converter

Chris HB9DAO has sent me a copy of his modifications to my SAQ VLF converter that was published a few years ago in SPRAT. His changes make the converter a bit more "bullet proof" in the European environment where there are lots of very strong signals in the VLF-MF frequency range. The schematic is attached.

TW Communicator Restored

I've just had an email from Tom Withers G3HGE who designed the wonderful range of TW Communicator transceivers for 160, 4 and 2m back in the 1960s. These UK products were ahead of their time being single unit transceivers for popular (single) bands. Tom has been restoring a 2m version and he sent me a photo of this (see left). It looks a real beauty. The TW brand is coming back, not with transceivers sadly, but with at least one new interesting product.

10m WSPR

Back on 10m WSPR again today. So far just the usual reports from G4IKZ although there is DX from Reunion Island coming through already. I've not been at all well lately so this has prevented me re-erecting my proper 10m halo well up on the mast. When back up, this should increase the ERP by several dB.

Back on 500kHz: 80th unique WSPR report received

This afternoon and this evening I'm beaconing (and listening) on 500kHz WSPR with the 1mW ERP. Just received my 80th unique WSPR report on the band, this time from G0NNF. Lots of Dutch stations are on 500kHz recently.

Namibia on 10m WSPR

Just spotted a new one on 10m WSPR today: V53ARC running just 1W from 8473kms away in Namibia was received at -23dB S/N. Also copied G3JKV some 123kms away, presumably by ground wave or tropo.

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.

Reunion Island copied again on 10m WSPR

FR1GZ has been copied very well here again this afternoon on 10m, some 15dB above the typical threshold for WSPR signals. He is running 10W, so there is a good chance he will copy my 5W from the FT817.

Reunion Is on 10m WSPR

This morning I was decoding the 10W WSPR signals of FR1GZ in Reunion Island at 9724kms. I was hoping 10m would open to the USA this afternoon and I'd hear some W and VE stations coming through in the ARRL CW DX contest, but nothing heard so far. 15m is full of USA CW stations though.

RF Cafe

This looks to be a very useful resource for both professional and amateur RF designers with lots of useful links, software and calculators available. See http://www.rfcafe.com/