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.

Still being heard on 500kHz

This evening the reports on 500kHz WSPR have been quite reasonable, despite the smaller antenna than a few months ago. Three unique reports from PA and from the UK so far this evening.

Blog visitor DXCC

Just noticed that this blog has been visited by people from 102 different countries this year so far.

Another new WSPR report on 500kHz

Last night I got another new 500kHz WSPR report, this time from PA0O in the north of the Netherlands at 440kms. This brings the total of unique WSPR reports on the band (via the internet database) to 83 stations plus a couple of others who reported by email. Overall the total number of unique reports on 500kHz including CW is 86 stations in 11 countries. Not bad for 1mW ERP. The most recent reports have been with my "degraded" antenna consisting of the 5m feeder to my 28MHz halo as a top capacity hat.

W1VLF's page about 8.97kHz experiments

Paul W1VLF is getting operational on the 33kms band (8.97kHz) and has already been received 5kms away running 50W into a base loaded vertical. He has created a website to detail the progress as he goes along. At the moment the website only has details of his HUGE loading coil. See http://rescueelectronics.com/9-Kilohertz.html .

82nd unique 500kHz WSPR report

This evening I got a new unique WSPR report, the first in 3 weeks, from Chris G3XIZ. This is my 82nd on the band. Chris has just started on WSPR and is likely to come on WSPR TX shortly. He is a very experienced 500kHz CW operator.

Auroral Chorus Recording (Paul Nicholson)

If you missed the streamed natural VLF auroral chorus emissions the other morning here is a nice recording made by Paul Nicholson in Todmorden UK.  It is a truly unbelievable sound, produced not by birds but by the auroral electromagnetic activity at VLF.