Earth-mode VLF RX kit updated

Today I've been updating my VLF receiving kit ahead of doing some further field tests, probably on Monday. I've now changed my RX loop so that the resonance can be adjusted in the field using a capacitance switch box to bring it to resonance.  The capacitance to bring it to resonance is around 240nF. The loop was about 1kHz off-tune so that the signal was around 4-6dB weaker than it should have been. Now I can tune the loop for maximum S/N in the field and can adjust the loop to a variety of test frequencies.  I've also peaked the 8.97kHz tuned circuit on my earth-electrode receiver input and fixed a faulty connection cable.

Whether these changes will allow me to get any further through the ground remains to be seen.

What a 500kHz WSPR signal looks like

G6AVK has his temporary grabber running on 500kHz this evening. See http://www.qsl.net/g6avk/ . It was interesting to see what my WSPR signal looks like on a grabber at around 80km away. My report was -24dB S/N but, as you can see, it is clearly visible FSK keying around 6Hz.

G3ZJO builds the G3XBM MF transverter

Over the last few days Eddie G3ZJO has been building a near carbon copy of my 10W transverter for 472/500kHz. I am pleased to hear that the build went well and Eddie is getting well over 10W RF from the unit.

G3ZJO's (very neat) version of my 472/500kHz transverter

Eddie found a couple of errors on my schematic (values shown on my photo are wrong on the circuit) and these I must correct. Once these had been sorted - my fault - the transverter worked fine. I see Eddie is getting some good reports on 500kHz WSPR this evening.

If anyone else builds a copy, please let me know and send me a photo.

Earth-mode 8.97kHz VLF tests

Today I did the first tests using my new 5W 8.97kHz beacon looking for signals at my usual "close" test site 1.6km from the home QTH. Good copy on QRSS3 and even solid copy on 10wpm CW. Copy was using my 30t 80cm loop on RX although results were similar using a 5m spaced earth electrode pair. Tests at greater range over the weekend. This is a recording of the 10wpm 8.97kHz CW signal at 1.6km .

QRSS3 signal at 1.6km using a 30t 80cm loop on RX

10wpm signal at 1.6km using a 30t 80cm loop on RX

As the traces show, there are a lot of strong interfering signals around in this part of the spectrum. With an E-field probe there were lots of telemetry like signals audible which I think are being carried over the national grid overhead cables. These were about 0.5km away from the test site.

Ten-Tec Argonaut VI

Ten-Tec is working on a new QRP radio that is a little larger than the FT817 but with a more conventional styling than the KX3. At the moment I understand price has not been fixed. 25 pre-production units are being field tested.  First shipments are not expected until later this year and there are hints that this may slip.

I am ambivalent about this new design: with limited HF band coverage and no VHF/UHF coverage and a styling that is "plain Jane" how many people will opt for it compared with (a) a new KX3 or even (b) an FT817 despite it being a 10 year old design? It needs to have some pretty strong unique selling features I think.

Interestingly, the Ten-Tec website makes no mention of this radio as far as I can see. Elecraft were forward selling the KX3 nearly a year before it made it out to first customers. Why is Ten-Tec not already seriously warming up the market? Surely if it is to be worth buying they should be encouraging potential customers not to buy a KX3?

The image above is linked from the www.qrper.com website.

Improved Software VLF Receiver

SWL Roland's enhanced SM6LKM software VLF receiver

An SWL called Roland from Germany has produced an enhanced version of SM6KLM's software VLF receiver, originally designed to allow reception of SAQ on 17.2kHz CW. The new version has:

•  44.1k/48k/88.2k/96k/176.4k/192k sample rate support
• More CW filters, SSB filter and AM filter added
• Spectrum display for audio frequency
• File-I/O for *.wav format (16bit)
• Left/Right channel select
• RMS signal level bar for audio level
• Muting (M) key
• Time+Date display, UTC or local time

This now makes the "enhanced" SM6KLM software receiver a superb tool for VLF use. Information and downloads are available at Roland's website https://sites.google.com/site/swljo30tb/

To use the receiver all that is needed is a VLF signal feeding into the mic input of the PC. Be sure you know what you are doing: the usual safe thing to do is to put a couple of back-to-back diodes across the DC isolated VLF input to prevent damage to the sound card. With an E-field probe antenna this receiver is capable of receiving many VLF transmitters from around the world. I shall be using it in future to monitor my 8.97kHz earth-mode CW beacon when out in the field testing.  

New VLF Beacon TX

Today I completed the build of my new VLF beacon transmitter. The beacon puts out 5W into a 50 ohm load, which is very close to the resistance of my 20m spaced earth electrodes. The beacon operates at either 8.970kHz or 4.485kHz with (a) continuous carrier, (b) 10wpm CW or (c) QRSS3.

VLF Earth-mode Beacon Transmitter

The main changes were to separate the keyer and the PA, mount the whole unit in a larger metal box and to use a 3C90 matching transformer with a fixed turns ratio having measured the ground resistance, which does not change greatly. On a continuous carrier soak test the case temperature only rises about 10 deg C, so frequency drift in the oscillator divider frequency source should be only around 0.1Hz at final frequency.

Having got the beacon finished, the next stage is to start work on some improved receiving kit and to see what sort of range can be achieved through the ground. My best DX so far with the original beacon was 6km, but this is certainly not the limit.

iPod Touch 4g - resetting

This evening I decided to do a "return to factory reset" on my Apple iPod Touch 4g as I'd run out of storage space on the 8GB machine and the battery life, despite regularly closing open apps, was getting very poor. I'd put this down to the age (2 years) and almost daily use draining the LiIon batteries.

So, I backed up the photos and videos, ensured the apps were safe on the main PC and pressed the "reset". Then I loaded iOS6.0 and all the apps back on the iPod. First impressions are that the battery life has just about doubled and appears to be almost back to what it was 2 years ago. I wasn't expecting this. To be honest, it feels like a brand new machine.

Although I don't buy that many modern gadgets the purchase of the iPod Touch 4g 2 years ago was one of my best ever purchases. It allows me to keep in touch with my emails, BBC, family by Skype and FaceTime video, WSPR spots monitoring, take photos and videos, Facebook, etc wherever there is a WiFi connection.  It slips in my pocket and is an almost constant companion.

My whole family are Apple converts!

Latest sunspot news

The latest from NASA:

The current prediction for Sunspot Cycle 24 gives a smoothed sunspot number maximum of about 75 in the Fall of 2013. The smoothed sunspot number (for 2012/02) is already nearly 67 due to the strong peak in late 2011 so the official maximum will be at least this high. We are currently well over three years into Cycle 24. The current predicted and observed size makes this the smallest sunspot cycle since Cycle 14 which had a maximum of 64.2 in February of 1906.

 The latest prediction graph from http://solarscience.msfc.nasa.gov/images/ssn_predict_l.gif

Charity jazz concert, Oxford Sunday Oct 7th

Final reminder: Tim Lapthorn Trio (jazz) at the Jacqueline du Pre Music Building, St Hilda's College, Oxford this Sunday at 1pm. Concert is raising funds for multiple sclerosis research.  Tickets from http://www.oxfordplayhouse.com/ticketsoxford/index.aspx?catid=24

or on the door. Good music, good cause. Please come if you can to support it.

Tim in one of his many appearances at Ronnie Scott's in London

My son Tim is a world class professional jazz pianist - see www.timlapthorn.com/ - and he is launching his new CD called "Transport" available later this month. Proceeds from the concert will got to the MS Society. 

If you cannot attend and want to make a donation to MS, please email me. Samples of his music available on his website.