Earth mode VLF test at 1.095kHz

When testing with utilities assisted earth mode in recent months I seemed to be getting weaker signals at 8.76kHz compared with my tests at 0.838kHz last summer. So, today I decided to go back and recheck results at a lower frequency at test sites 1.6, 2.6, 4.5 and 5.1km away from the 5W QRSS3 transmitter at home. Test locations were rural fenland roadsides, a National Trust car park and 2 roads in the next villages.

I used the same TX as at 8.76kHz, but divided down by a further x8 to 1.095kHz using the 4060 divider. The receiver was a horizontally orientated 30turn, 80cm across, series tuned loop into a low impedance MPF102 FET preamp with a drain circuit peaked at around 1.1kHz and emitter follower into PC running Spectran.

My initial test at 1.6km was a total failure - no signal visible at all in Spectran at 0.73Hz bandwidth. Then I realised that I had BOTH the garden earth electrodes in use at the TX (neither connected to pipes). A phone call to my wife and one wire was connected to the pipework in the house with the other still connected to the earth electrode at the bottom of the garden some 20m from the house. The signal then appeared at good strength.

Signals were received at all test locations indicated, but there was no signal visible (in QRSS3 bandwidths at least) when moving away from the roads into nearby fields or at some other test locations where pipes were absent (or plastic). At one location I rested the loop within 2m of one of the fenland water courses, but nothing was detected. The image attached  is the signal at 4.5km, which is strong in 0.79Hz bandwidth. Even stronger signals are possible with more optimum positioning, but I keep having to move my loop to avoid it being crushed by oncoming farm tractors! I do get some odd looks too.

My conclusions from the tests to day are:

• This was definitely utilities assisted earth mode. The initial (accidental) test today with 2 earth electrodes not connected to water pipes failed.
• Signals are strong close to where the metal pipes are, but rapidly disappear where no (metal) pipes are close by.
• Signals at 1.095kHz are definitely stronger than at 8.76kHz in the 3-5km range.

There is one more test to do at some point that needs some assistance locally (I think within 10km to work). I want to try a long stable carrier test with someone looking in the very narrow bandwidths we've been using for the radiated tests recently. What I'm wondering is just how far from the pipes does an earth mode signal "leak"? Using Spectrum Lab with the very weak signal bandwidths like 0.4-2mHz, the weak remnants of a signal might just be visible some way from the "easy" utilities assisted coverage area.

The remaining tests I want to do still with earth mode are:

• River bank or sea coast test - just how far can one get?
• True earth mode in open country without any utilities assistance
• Earth mode at higher frequency e.g. around 70kHz, which I can manage with my present set-up. Based on recent OFCOM correspondence I believe such tests would be legal as long as there is no intentional radiated signal or interference to others.

This class of experiment is not in the same league as those being done by the radiating VLF DXers, but fun nonetheless, especially as anyone can do this sort of test without NoV or special permits needed.

111km optical QSO in Yorkshire

G8AGN/P and G0EWN/P achieved a 111km speech QSO on optical communications using 0.5W red LEDs and Fresnel lenses on April 6th 2011. Brilliant stuff.

Heathkit from 50 years ago

Dave G3UUR pointed me in the direction of the 1961 American Heathkit catalogue in which I found the EW19 electronic workshop kit. My memory had this as the EW1, but I must have got this wrong. My mum and dad bought me this for Christmas 1961 and it was this that got me started in radio as a hobby.  The Medium Wave radio was used for my first DXing late in the evenings. Also, the simple MW transmitter (using the crystal earpiece as a mic) got me across the house - my first transmissions.

SAQ 17.2kHz this week

There will be an extra transmission with the Alexanderson alternator station SAQ on 17.2 kHz on Thursday April 14th 2011 at 12:45 UTC with tuning up some time before.   The transmission is directed to "The 5th European Conference on Antennas and Propagation" in Rome, Italy. There will be no QSL verification of this transmission.

An odd ladybird in a London park

During a picnic in London's Springfield Park today, a very strange ladybird (family name Coccinellidae) came to join us. I've seen red ladybirds with black spots and vice versa, but never a yellow one with white spots! Anyone know what sort it is?

Bell System Techical Journal now online

The complete Bell System Technical Journal from 1922-1983 is available on line and searchable. See
http://www.alcatel-lucent.com/bstj/ .

G3XIZ testing on VLF overnight tonight

Chris G3XIZ will be active on VLF again this evening and overnight on 8.9766616kHz although the start time is not yet known. My VLF on-line grabber is already on in readiness, as is the grabber at G3ZJO. Chris has recently been improving the match to his VLF loading coil and antenna and is working on a new variometer.

Optical Comms DX

The latest RSGB news reports that G8CYW and G8KPD have set up a new UK record for optical DX over a distance of just under 90km in NE England using SSB and FM with a design that appeared in a recent RadCom.

10m WSPR

10m WSPR reports (5W to a halo)

Another good morning on 28MHz (10m) today with WSPR reports from 4 different Australian stations plus RA9 and G's by tropo (I assume at 250km).  I was also copying VQ9JD on WSPR.

Transequatorial 70MHz QSO

SV2DCD and ZS6WAB have had the first ever 70MHz transequatorial (TEP) QSO on 70 MHz. It has also been announced that Namibia now has access to the band. Watch the video.