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.

Over-the-horizon on 480THz

My order for 3 off 12W red LEDs known as PT54 Phlatlights has arrived. These are VERY VERY bright LEDs mounted onto substantial heatsinks which emit a strong signal on 480THz. They were originally intended for portable projection systems. One of mine is going into my QRO optical beacon running continuous carrier, CW, DFCW, QRSS3 or QRSS30 to use in further over the horizon (non line-of-sight) beaconing tests using the scatter from particles in clear air and the reflection off the base of clouds. Last winter my own simple beacon running at around 300mW was detected several km over the horizon using QRSS3. G4HJW's optical beacon using a Phlatlight LED was detectable in my village some 8-9km over the horizon. In neither case could the red glow from the TX be detected by eye.  This week I also received some SFH213 10 degree half angle PIN photodiodes which should be considerably more sensitive than my BPW34 detectors currently in use. Estimates suggest at least 6dB more sensitivity.

Together, the QRO optical beacon running from home, focussed with a 100mm lens (gain about 24-30dB), and a portable high sensitivity 100mm lens based detector should allow plenty of scope for innovative NLOS tests on dark winter evenings.

Just realised: 5W out (for example) into a 30dB gain lens "antenna" is equivalent to 5kW of light power in the beam. That is SOME bright light. Clearly great care is needed in siting and aiming such a system to ensure safety.

New soldering iron needed

My old Weller soldering iron station (an old Pye Telecom chuck-out from about 1980) is on its very last legs - it is physically cracked and really does need replacing. You can tell how old it is by the mains wire colours! It was possibly the one I had on my bench when I started work in 1970.

I'm looking at the Maplin soldering iron range for a replacement, which look good value. Most of my work is with discrete parts but increasingly some SMA parts are being used too. Up to now I have been using up my stock of tin-lead solder, but am happy to move to lead free.

So, please may I have your recommendation on what soldering iron to go for?

I don't mind spending a bit more if by doing so I get a more reliable soldering station. Clearly replacement tips must be available inexpensively.

3C90 cores at 8.97kHz

The output of my TDA2003 based VLF earth-mode transmitter is around 5W into 4 ohms. The new semi-permanent earth mode "antenna" just installed measured at around 50-60 ohms resistive at 8.97kHz.  I used an AC potential divider technique to check this. Today I wound a small 3C90 based transformer using the advice I got from various people yesterday and it works very well, matching the TDA2003 perfectly to the earth electrode pair. I managed to destroy my K1EL message keyer's 5V regulator (and the keyer IC too!) so a rebuild is required before I go out into the field again to do some RX measurements. All being well these new tests will start in the next few days.

My SFH213 PIN photodiodes arrived today and my 12W Phlatlight LEDs are due next week. I'd better crack on with the new VLF earth-mode tests before these arrive as I will want to try some over-the-horizon 481THz tests with the more powerful optical transmitter and more sensitive detectors.