VLF very long carrier period tests Dec 15th

This Wednesday, Dec 15th, I will run tests on 8.7608kHz with very long continuous TX periods of several hours interspersed with gaps of 0.5 to 1 hour. Transmissions will start at 0900GMT and finish at 2300GMT. I will reveal the TX pattern after the test so the test is done "blind".

I'd be most grateful if suitably equipped stations could look for any possible signs of the signal, even though I shall only be using the 20m spaced earth electrodes and 5W as used for my local earthmode tests. Those able to screw the bandwidths right down may just be able to detect something, although I think it is unlikely at any great distance.

15.12.10    
0900-2300z 
8.7608kHz   
Carrier "on" periods of 30mins or more

Good luck to anyone having a go.

73s
Roger G3XBM

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How far is possible with earth mode on the Dreamer's Band?

A further observation from the test today: with 17dB above the noise signals at 5.1km using QRSS3 there is plenty of (theoretical) range still to be had with utilities assisted earth mode and just 5W.

Assuming 18dB loss every time distance is doubled (an inverse cubed attenuation rate for induction/conduction - is this right?) then almost 10km should be just possible, assuming the utilities that are aiding propagation are still there in the ground. Going from QRSS3 to QRSS30 should give another 8-10dB (see http://www.qsl.net/on7yd/136narro.htm#QRSS). Increase power from 5W to 100W gains another 13dB, so QRSS30 and 100W could give a range of some 20km by utilities assisted earth mode in favourable locations.

So, in some locations using the utilities buried in the ground all around us could offer some quite decent ranges with an earth electrode "antenna" at the TX end that requires minimal matching and no large loading coils, just a step-up transformer.

What is less clear to me is what exactly is the signal being carried along? Water pipes (often these are plastic now), overhead mains cables, gas pipes (usually non-metallic), phone lines, rivers even?

8.76kHz tests with loop + earth electrodes on RX

Today I did a test at 5.1km to compare reception of my 8.76kHz 5W transmission using (a) an 80cm loop antenna and (b) a small earth electrode antenna (14m spacing) using a variety of preamps.  Although quite solid reception (17dB S/N in 0.18Hz BW) was achieved using the loop laying flat on the ground, there was absolutely nothing detected using the earth electrodes, which was both surprising and disappointing. I used the very same preamp in both cases and also tried the lo-Z input tuned preamp with the earth electrodes that successfully copied DK7FC at 648km last weekend.

Several possibilities for the failure with the earth electrodes:

• The electrode spacing was far too small
• The barbecue skewers used as electrodes were too short and not making decent soil contact
• The soil was too wet, so the pick-up was lower than with dry, low conductivity soil. The test site is in the fens where the soil is a dark peat.

Next step is to repeat the test up on the chalk uplands to the south of the QTH where soil conductivity will be lower and to try a larger earth electrode spacing on receive.

A Homebrewer's Lab

VU2ESE's workbench - not unlike mine!

Ashhar Farhan VU2ESE has an interesting page setting out what basic equipment he considers a QRP homebrewer needs. See http://www.phonestack.com/farhan/lab.html. The only additional piece of equipment that I have found really useful is a small box to measure inductors and capacitors. The LC Meter kit produced by the Cambridge and District Radio Club has proved invaluable. A small spectrum analyser would also be useful, but these do not come cheap, although there are designs on the internet to make simple ones.

500kHz WSPR with earth electrodes

This evening I tried WSPR on 500kHz again using the earth electrode "antenna". 4 different stations reported hearing my sub 1mW ERP signal with best DX 417km to PA0A. Tomorrow I may try 500kHz with the vertical antenna to see how it compares, although I have to rebuild the ATU first.

DK7FC's report on his 9th VLF experiment

DK7FC with his VLF loading coil

Stefan has summarised the results of his latest tests on VLF. This is well worth reading with best DX 2873km and lots of new stations receiving his transmissions for the first time.

This picture was taken by a friendly visitor and there are more pictures at http://mkorbit.de/2010/12/05/weltrekord-signalubertragung-auf-einer-langstwelle-vlf/

USA on 10m

At 3pm this afternoon KC2GMM was coming through on 10m WSPR at -25dB S/N when running 10W. Another example of the power of WSPR to spot the fleeting openings.

Realtime Propagation Charts

G0KYA has a most useful page offering realtime propagation predictions in the form of maps showing exactly where signals should reach on a given band at a given time of day. It uses the latest available solar data so should be a very good guide. The maps assume 100W and a dipole at medium height, so for a QRP station the results to be expected will be less good.

VLF real DX: 2873km on 8.97kHz

Yesterday, Sat Dec 4th, DK7FC's VLF signal was copied by 4X1RF at an astounding distance of 2873km. Signal levels suggest that transatlantic reception may indeed be possible in the near future. Many other stations also copied Stefan's signals on various VLF frequencies yesterday. Congratulations to Stefan and everyone else who managed to copy his signal.

Full QTH locator square? Find it here

Just discovered that my full QTH locator is JO02DG85VD . This was found using a website I'd not come across before http://no.nonsense.ee/qthmap/ .