VLF amateur DX in Poland (290kms) on 9.6kHz

Marcin SQ2BXI has sent me this message today (April 17th 2010):

In last night we have VLF eksperiment in 9,6kHz in SP2KDS Club.Club signal copied Jacek SQ5BPF -distance 290km.
Movie tranmiter: http://www.youtube.com/watch?v=2sn6AmpkwlU&feature=player_embedded
and Polish page: http://www.sp2kds.pl/136khz/298-pierwsze-proby-nadajnika-w-pamie-marzycieli.html

Next experiments will soon have to 8.970kHz...
73! Marcin SQ2BXI

Next 8.97kHz German test delayed 2 weeks

Stefan DK7FC says it will be a couple of weeks before his next VLF test transmission on 8.97kHz. This gives me more time to get the RX ready.

Icelandic fireworks - lots more to come?

Volcanic activity on Iceland appears to be getting worse with more activity recently. Disruption to air flights in the N.Atlantic may become more common. See this article in New Scientist.

Ham and other books on eBay - still time to grab a bargain

My ham and other books including some magazines about the remote island of Tristan da Cunha (ZD9) selling on eBay still have a few days to run, so you still have time to get a bargain. Check out http://myworld.ebay.co.uk/rlapthorn

Even greater DX on 8.97kHz?

Stefan DK7FC has now got his 600W 8.97kHz VLF PA working and is waiting for a windy day to get his kite supported antenna up in the air. With a few dBs more power and more well-equipped stations listening/watching on 8.97kHz (33kms band) Stefan is hoping that >1000kms can be spanned in the next test transmission.

Rockmite 20m kit (unbuilt)

For some time now I've had an unbuilt Rockmite 20m QRP transceiver kit waiting to be put together. The problem is I have so many other things on the go that a 20m QRP kit is way down the list and 20m was never my favorite band: I'd wanted a 40m kit but they only had 20m ones in stock when I bought it over a year ago. The kit has never been opened and I'm thinking about putting it on eBay. The current price for the kit in Europe is 45 euros plus shipping.

What would be a fair price?

Free power transmitters

Mike AA1TJ has sent me an interesting letter about using thermoelectric modules to generate a few milliwatts of power from body heat. This got me thinking about the other ways of "harvesting" free energy from vibration, movement, heat, mains hum fog, RF from radio stations etc. One bizarre idea from a few years back was a leg-brace that powered a mobile phone by leg movement (see left). There are ICs coming onto the market that scavenge energy from various sources allowing low powered devices to be powered for free. The challenge for us QRPers is to think of creative new ways to generate a few milliwatts to get signals across oceans. Who will be the first to work DX using RF rectified "off-air" from the local FM radio or TV transmitter?

Talk request from Peterborough CLub

Having given a talk about "kitchen sink" simple radio last year, the good folks at Peterborough have kindly invited me back to talk about sub-9kHz radio. Date confirmed as Wednesday Aug 25th 2010.

Some ham books of mine on eBay

Today I've put a few of my books for sale on eBay. They include RSGB and ARRL handbooks. If you are interested do take a look. If you live in the Cambridge area and want to pick them up locally then there will be no postage to pay. See http://myworld.ebay.co.uk/rlapthorn

Thoughts on VLF Earth-Mode and Induction DX

Earth-mode (through the ground conduction) and induction communication (mutually coupled coils) have an inverse cubed attenuation with distance. Think about this: I reached 0.3km with earth mode for an audible CW signal with around 4W RF and a simple 5m base receiver and 10m base transmitter. To double this range, all other things being equal, means increasing power by 18dB to 250W. To double range again means raising the power to kWs. Conversely, improving the detectable sensitivity threshold by 18dB (increasing the electrode spacings at each end, using WSPR or QRSS, etc) reduces in power needed for a given range dramatically: my 4W signal could be detected at 0.6kms or a just a 63mW signal could be detected by earth mode at 0.3km. In reality, especially in urban areas, water pipes and cabling may help "propagation" and achievable ranges may be greater. DX is relative, especially with conduction and induction at VLF.