Loop TX antennas at VLF

At first sight the idea of a 10m x 10m wire loop as a TX antenna at 8.97kHz VLF sounds a non-starter as a way of radiating any useful power. Having tossed the idea around with others though it appears that, although very inefficient, it would not be that much worse than a smallish Marconi vertical because these antennas need very large (and lossy) loading coils, height and good grounds to be effective. With 100W to such a small loop around 0.45uW could be radiated. Already G3XIZ has spanned 218km with just 2uW to his vertical, so for small gardens the VLF TX loop is worth a look.

G3XIZ and DJ8WX on 8.97kHz

The Spectrum Lab plot showing reception here again of these two stations around 8.97kHz VLF. Both were using back garden antennas. DJ8WX is around 645km away. G3XIZ about 45km.

GPS cannot always be relied upon

As if to remind us of the vulnerability of modern technology yet again:

The MoD has informed OFCOM of the following GPS jamming exercise

Dates: 19 – 26 May 2011.

Times: limited periods between 0700z 19 May to 100z 2 May 2011. 

Location:  The ground based radar jamming events will take place in the SW approaches against the remote radar head at Portreath 21-22 May, undertaken by F-18 Growler aircraft. Additionally there will be radar jamming against deployed targets in South West Wales throughout the period 19-26 May. Communications and airborne radar jamming will take place throughout the same period on the East Coast with aircraft operating within the North Sea Military Danger Areas. Communications and maritime unit radar jamming will take place in the SW approaches and Bristol Channel. Falcon aircraft will operate from Sea Level to FL240 unless jamming AEW aircraft where they may operate above FL245.

Note: Safety of life operations will take precedence over exercise activities at all times.

Emergency radio kit

The terrible Japanese earthquake, tsunami and nuclear crisis has reminded us all that modern 1st world technology cannot always be relied upon. The UK Foreign Office and the BBC have webpages suggesting essential items as an emergency "grab bag" to have ready in such circumstances. One of the attractions of simple QRP gear is its ability to work when nothing else may, for example using a small battery or solar cells with a compact CW rig that can be taken anywhere with a throw-out HF antenna. In the event of a sudden and unexpected disaster, would you and I be able to communicate still?

8.97kHz very sensitive spectrogram online

Paul Nicholson in Todmorden, Yorkshire UK has put on line his steerable and highly sensitive spectrogram for the VLF Dreamer's Band around 8.97kHz. Paul's system is super sensitive and detects just about anything going. His new spectrogram can be "steered" to a specific direction and the display clicked to show exact frequency and S/N levels. There is also a roll back function so that records from a few hours to days back can also be checked. Marvellous! See http://abelian.org/vlf/fbins.shtml

Great care needed when IDing VLF stations

A word of caution to those of us looking for very weak signals around 8-9kHz. DJ8WX was copied here overnight on 8.970022kHz without any doubt and my grabber was clearly able to see his close-down around 0700 today. The frequency and the trace timing corresponded perfectly. Likewise with G3XIZ and DK7FC/P some weeks ago.

This evening I was looking very carefully again at the Spectrum Lab screen from the last 24 hours in 424uHz BW and readjusting audio gain ranges, screen colour saturation and contrast. Out of the noise appeared another very very faint line, not at 8.970022 but at 8.96998kHz. I've attached the screen shot here (I have overlaid it with the time for clarity).

My immediate reaction was this must be Ossi OE5ODL as this is the frequency he uses. Then I checked his grabber and saw he was not operational overnight last night! So, what looked like a trace on his frequency cannot be him. It must instead be some artefact of SL or something else. We have to be very careful when seeing traces at very specific VLF frequencies: it may be an indication of a given VLF amateur station, but without some modulation or turning on/off of the carrier a doubt remains.

Sadly I don't think I did see Ossi today after all, but I shall keep looking.

New Sub-9kHz Amateur Radio website

For some time I've wanted to tidy up the pages on my website that dealt with the various aspects of VLF amateur radio below 9kHz. So, today I've launched a new site entitled Sub 9kHz Amateur Radio bringing together my information more accessibly. The original pages just grew and grew as activity at VLF just took off. It is almost 1 year to the day since DK7FC made his first historic DX on 8.97kHz. Since then we've come a VERY long way!

The new site has a table showing the VLF DX records. This is not fully populated or correct yet, so I need everyone's help to get this up to date in the next couple of days please. If you are aware of errors or omissions please let me know right away.

Another addition - to be much expanded - is a page on TX stations and their equipment. Please let me have photos, schematics of antennas, transmitters, loading coils etc.  Another page deals with the kit needed to receive on the Dreamer's Band. It is easy stuff that can be built by anyone. Also a page linking the various software packages available freely. Yet another page lists the VLF grabbers (incomplete still - tell me of others!) which are such a vital resource. 

Also included on the page is more data on earth mode (through the ground) communication which is a very accessible way of starting out on VLF as much of the kit is re-usable for experiments with radiated VLF tests (same loops, probes and pre-amps can be used).

Please let me have constructive feedback so I can make this as good as possible. I hope you enjoy the site.

The end fed halfwave antenna (EFHW)

Steve G0KYA has a nice pdf document he's created describing how to make simple end fed half wave antennas (EFHQ). These band specific antennas can be very effective and simple when mounted either vertically or horizontally. They can be made with PVC covered wire, fishing poles or aluminium rod. See http://www.infotechcomms.net/downloads/Endfed_halfwave_dipoles.pdf.  Many years ago we experimented with these on VHF handhelds and achieved results some 6dB better than with a standard 1/4 wave whip, but on 2m they were on the long side! On HF they are capable of low angle radiation good for DX.

4m QRP success - 229km today in the contest

Using my small 1W QRP 4m transverter recently built into my loft dipole I've just managed a QSO with G4RFR 229km away in Dorset (IO90AS) using CW in the RSGB Cumulative contest. He was on SSB and it was hard work, but in the end a full exchange was made.  Also heard G3EDD, G4ASR, G3BCU, G3TCT, G4DEZ, G1EHF on the band on SSB and G4ZTR on CW.

DJ8WX copied again on VLF (645km)

Uwe DJ8WX is currently transmitting a long dash on 8.90022kHz and his signal was copied well on my VLF grabber overnight in a 424uHz bandwidth. Also visible is a mystery signal around 8.9701kHz that most people think is some sort of local noise source but it is very repeatable every night.