DK7FC's 8.97kHz VLF grabber active antenna

DK7FC runs a grabber on 8.97kHz so he can monitor signals testing on this VLF frequency. He feeds the signal from this active antenna into his PC's soundcard. This is a sketch of the schematic that Stefan posted on the LF reflector today. He has since added some additional C between the drain and ground to reduce the intermod products from LW/MW broadcasters that otherwise produce a strong line on 9kHz.

VLF up-converters and MOSFETs

Today I built a MOSFET up-converter, converting 7-9kHz VLF to around 20MHz. However, I was disappointed with the results: low conversion gain and sensitivity when using either a 3N211 and a BF981 device. I used an 82mH choke with a 4n7 cap as the tuned circuit on G1 (tapped capacitance for max sensitivity with 50 ohm input) with LO injection on G2. Despite optimising everything I couldn't better the sensitivity achieved with the SBL1 based up-converter that appears on my website.

Filter Calculator (and other calculators)

When designing a simple Sallen-Key active filter yesterday for my VLF receiver I found several useful web resources. One of the best is http://www.calculatoredge.com/index.htm#electronics that has a lot of useful calculators for electronics. I like the fact that when designing filters it asks you, and gives you, values in "real" numbers like nF and kohms. Some calculators ask you to give values in Farads and ohms to the power E-09 and similar and are obviously written by a college professor and not a real engineer who finds it hard to work these out!

Sub-9kHz NoV - still awaiting Met Office OK

I chased Rod at OFCOM this weekend to see if there was any further news on the NoV application to TX below 9kHz. The hold-up is still the Met Office, from whom OFCOM are awaiting approval. I'm carrying on with sub-9kHz earth-mode and induction tests at 4W meanwhile as I can't imagine anyone will object. My transmissions last about 10 minutes and the radiated power is picowatts!

Earth mode and induction testing at 1kHz

Today I restarted my earth-mode and induction communication tests at VLF using with my 4W transmitter and 10m separated earth electrodes. After some false starts, I ended up by field testing a simple receiver consisting of 30t of wire 80cms square into an active high pass filter followed by 3 stages of audio gain into a crystal earpiece. 2N3904 transistors were used at each stage. With the loop over my shoulder I set the TX sending 1 second "beeps" at 1kHz and went walking....

Even with 20-30dB of 50Hz rejection it was still an issue in many places. Walking across the field behind my house, and well away from cables and pipes, the signal could be heard in the earpiece at RS53 to a distance of 0.35km. Mains hum and LW/MW interference (the RX is not in a screened box) rather than signal level  limited further range. This week I'll add more high pass filtering, put the RX in a screened box and make the whole thing more immune from BC breakthrough. As I can hear this signal by ear at 0.35km with essentially no narrow filtering, then I'm confident that twice as far will be possible with QRSS/WSPR and a PC based receiver. Not bad for 4W at 1kHz.

10m Es

Put the 10m QRP WSPR beacon on early today and already there are spots from the G, CT and OY. The sporadic-E season is gathering pace.

The Spirit Level - a book I recommend

"The Spirit Level" is a book by Richard Wilkinson and Kate Pickett published in the UK by Penguin showing hard evidence that almost everything - from life expectancy to mental illness, violence to illiteracy - is affected not by how wealthy a society is, but by how equal it is. Societies with a bigger gap between rich and poor are bad for everyone in them, including the well-off. It is a book full of positive solutions and shows how we can move towards a happier and fairer future.

The Limerick Sudden receiver kit

The GQRP club has launched a new kit called the Limerick Sudden. This was the message from George G3RJV today on the GQRP Yahoo Group:

"Limerick Construction is an exciting new way of construction. Conceived by Rex Harper, W1REX, of Limerick Maine it offers a simple and attractive way of building equipment. Based upon the Manhattan construction method (surface mounted parts on insulated pads) it also lends itself to the production of easy to build kits.

For some months G3RJV, G3MFJ and W1REX have been looking into producing a basic receiver kit in Limerick format. The resultant project, based on the G3RJV Sudden is now available in kit form. See http://www.gqrp.com/sudden.htm . It is complete in every way ... all parts... board ...case...no coils to wind ... even a battery! We hope members will enjoy our new Club Sales offering. "

Shoe power source (from Elector Newsletter)

A novel way of generating a small amount of power using a piezo-electric generator within a pair of shoes is shown in the latest Elector Newsletter.

Useful Simple Signal Generator

Dom Baines has a useful blogsite and today I noticed this NorCal circuit on his page for a multi-band S9/S1 signal generator. It uses a switched crystal oscillator with 2 well-defined output levels at 50uV and 1uV, so is ideal to test receivers.