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/ .

144MHz WSPR

For the first time I tried WSPR on 2m this evening. G4IKZ at 18km was a VERY strong signal but with a huge amount of Doppler shift which meant he did not decode. I've just seen G4IKZ has spotted me at +3dB S/N though, so perhaps it was just a passing plane.

DK7FC's 8.97kHz signal copied today (and in Israel!)

Weak signal around 8970.0Hz

Today I managed to weakly copy DK7FC's latest test transmission on 8.97kHz using my 20m spaced earth electrode and small FET preamp. Spectrum Lab, locked to a VLF MSK transmission helped by allowing me to look at precisely the right frequency. Distance is 648km. Stefan's signal was also copied in Israel, quite remarkable DX.