German VLF earth mode test: 5.2 km on 8.97 kHz

Stefan DK7FC has been doing some experiments with around 50W to a 300m spaced grounded earth electrode "antenna"  in a remote location in Germany. Today his experiments were successful with his transmission of 30 minutes clearly received on his E-field probe receiver and grabber located in the city some 5.2km away.  See the report on his experiments at  http://www.iup.uni-heidelberg.de/schaefer_vlf/VLF_5km_with_an_earth_antenna.pdf . Stefan can improve the electrode arrangement and increase current into the ground as well as run up to 500W. He's hoping to see the signal on the DF6NM VLF grabber located 174km away. If successful, this would be the first reported amateur radiated VLF DX using earth electrode antennas.

2-way QSO on the 8.97kHz "Dreamers Band"

DJ2LF and DF6NM held what was probably the first two-way contact on 8.97 kHz. The distance between them was 20.2 km, well outside the reactive near field zone (λ/2π = 5.3 km). In each case the radiated power was about 5uW. They used a special QSO procedure using dual frequencies. Congratulations to both stations.

Resonating the VLF receiver loop

Today I've been resonating my receiving loop to see if this improved things. Well, I tried it - no better. Then I improved the active high pass (50Hz) filter which got the mains hum down some more, removed an audio gain stage in the RX just leaving 2 common emitter stages. With this, 4W TX, and the loop resonated around 2kHz I did a further walk-about test. 0.42kms was the limit of range. S/N better and 50Hz hum not a problem even close to cables. The RX needs some more gain and narrower selectivity.

M0BMU's latest complete 8.97kHz Portable Receiver

Jim Moritz M0BMU has updated his loop/preamp circuit for 8.97kHz turning it into a complete direct conversion receiver for 8.97kHz. He posted this on the LF reflector in the last few days. I have added this to my sub-9kHz website (scroll down for Jim's description and schematic on the webpage. See http://sites.google.com/site/g3xbmqrp/Home/10khz

Further 8.97kHz DX tests from Germany

DK7FC conducted more tests on 8.97kHz last weekend. Best DX was 300kms mainly because the noise levels are now higher than in the earlier tests. However it allowed Stefan to test some new equipment successfully.

DK7FC's VLF PA

Stefan DK7FC posted the 300W PA used in his historic tests on 8.97kHz on the LF Reflector today. He's been copied by at least 10 stations in 5 countries using this PA with best DX 902kms.

4W TX for sub-9kHz experiments

Attached is a picture of the "transmitter" I'm using for my ground and induction communications tests. It uses a TDA2003 audio IC into a toroidal step-up transformer that can match from 10 to 150 ohms. Not sure of the transformer type which came from an old Pye Telecom PMR radio, possibly an M206, Whitehall or similar (it was used on the audio stages). I haven't yet tried listening with an active probe antenna to see how that would perform. Time is limited, so further tests may have to wait until the end of the month. Best range so far, receiving "by ear" on a loop antenna, with no clever selectivity or signal processing, is 0.35km.

DK7FC's 8.97kHz VLF grabber active antenna

DK7FC runs a grabber on 8.97kHz so he can monitor signals testing on this VLF frequency. He feeds the signal from this active antenna into his PC's soundcard. This is a sketch of the schematic that Stefan posted on the LF reflector today. He has since added some additional C between the drain and ground to reduce the intermod products from LW/MW broadcasters that otherwise produce a strong line on 9kHz.

More VLF DX TX tests by DK7FC planned

Stefan DK7FC is applying for permission from the German authorities to erect a 300m long kit supported antenna for his next transmitting tests on VLF. Before this is possible he hopes to test with a 200m long kite antenna. The main concern now is summer noise levels on VLF and the effect this will have on DX possibilities. Some ionospheric propagation simulations by SQ7MPJ suggest that attenuation over an 800kms+ distance would be a few dB less if the TX frequency was reduced to around 5-6kHz instead of 8.97kHz because of the effect of the D-layer.

8.97kHz noise levels

DK7FC has delayed further DX tests on 8.97kHz because of thunderstorms in Germany. Stefan comments that the noise levels appear to be rising as thunderstorm activity increases as we move towards summer. He is wondering if further VLF DX tests should be postponed until the autumn when the noise will lower again. You can check UK thunderstorm activity on the Nowcast website.

8.97kHz RX started

Today I made the loop antenna for the front-end of my 8.97kHz receiver. This consists of 24 turns on an 80cms square frame (the most I could wind with the 0.2mm PVC covered wire I had). Next stage is to resonate the loop and add some gain and selectivity so it can be used with a PC based SDR such as SpectrumLab or with a stand-alone direct conversion receiver.

Next 8.97kHz German test delayed 2 weeks

Stefan DK7FC says it will be a couple of weeks before his next VLF test transmission on 8.97kHz. This gives me more time to get the RX ready.

Even greater DX on 8.97kHz?

Stefan DK7FC has now got his 600W 8.97kHz VLF PA working and is waiting for a windy day to get his kite supported antenna up in the air. With a few dBs more power and more well-equipped stations listening/watching on 8.97kHz (33kms band) Stefan is hoping that >1000kms can be spanned in the next test transmission.

W1VLF's page about 8.97kHz experiments

Paul W1VLF is getting operational on the 33kms band (8.97kHz) and has already been received 5kms away running 50W into a base loaded vertical. He has created a website to detail the progress as he goes along. At the moment the website only has details of his HUGE loading coil. See http://rescueelectronics.com/9-Kilohertz.html .

DF6NM and DK7FC active on 8.97kHz today

Not one, but 2 stations were active on 8.97kHz today in DFCW mode. Part of DK7FC's transmission was copied at 902kms away in Warsaw and DF6NM, running a much smaller station and antenna, was copied 21kms away. A first QSO on the 33kms band cannot be too far away now!

4th Amateur VLF test transmission on 8.97kHz this weekend

Stefan DK7FC is planning to transmit again on 8.97 kHz VLF if the wind is able to support his kite antenna. The tests start Saturday April 3rd, at around 1000 UTC. The mode used will be DFCW-600 (dual frequency very slow CW). Several stations across Europe will be listening some using tiny E-field probe antennas.

A WSPR first on 8.97kHz

This afternoon I set up my "earth-mode" station using a pair of electrodes about 10m apart in the garden, one near the house and one at the bottom of the garden. Using my 4W audio amp driven from the WSPR software in the PC I transmitted a WSPR signal on 8.97kHz. With a separate PC at the other side of the house and with 1m of wire as the "antenna" plugged into the mic socket of the PC I went listening for my WSPR signal.  Sure enough, there was my earth-mode transmitted signal at -15dB S/N. Distance was only about 10m but at least the TX, WSPR system and ground electrodes work, so I now can go out into the fields behind my house to look for my WSPR beacon using a decent, sensitive 8.97kHz RX next time. Strictly I need my sub-9kHz NoV to do this test, but as nothing is radiated I doubt anyone will care.

As far as I know this is the lowest frequency on which WSPR has ever been successfully used.