VLF Amateur Radio. Roger Lapthorn G3XBM. Feb 10th 2012

Transcription

1 VLF Amateur Radio Roger Lapthorn G3XBM Feb 10th 2012

2 Topics to cover The VLF spectrum and its uses Equipment needed for VLF RX and TX VLF earth-mode through-ground tests VLF 8.97 khz radiated DX Getting involved it s simple and inexpensive.

3 The Sub-9kHz VLF Spectrum Wavelengths are VERY long below 9 khz. VLF TX antennas are huge. Signals go through water and rock better. Bandwidths are narrow data modes only Reliable world-wide range, with enough power

4 VLF/ULF/SLF Users Mainly the military (submarine comms + navigation): khz Military MSK and time signals khz Navigation systems (Alpha/ old Omega) 8-9 khz Sferic detection systems 1-8 khz Natural emissions detection Hz Submarine comms (ZEVS/Sanguine) 50/60 Hz Power distribution

5 Amateur VLF 8.97 khz being used for tests in Europe Earth-mode* tests between 0.8 khz -17 khz khz allocated to UK amateurs by NoV *.an explanation later

6 Modes for VLF QRSS3, 30, 120, 6000 = Slow CW mode DFCW = Dual Frequency CW WSPR Continuous carrier (for days!)

7 Receiving VLF signals High man-made and natural noise 9 khz LF/MF signal intermodulation QRM Big antennas not needed on RX Equipment is simple to build Free software available to help detect weak signals

8 VLF Receivers Sub-9 khz signals can be directly detected and fed into phones or PC. No need for up-converters and HF RX. PC used for filtering and weak signal processing Main issue is dynamic range and S/N Need an E-field probe or a loop Need a preamp with good dynamic range

9 VLF RX Loop Antenna 80cm, 30turn tuned loop Hand carried/rotated or placed on ground For home use a large vertical 1t wire loop OK

10 VLF Preamp Built in a small box Powered by rechargeable 9V battery Inexpensive

11 VLF E-field probe

12 VLF loop preamp

13 Earth Electrode Antenna Earth rods in ground 20-50m apart or One earth rod + connection to house metal water pipes

14 VLF PC Software Needed to detect VERY weak, long duration signals deep in noise SM6LKM s tuneable VLF receiver program Spectran Spectrum Laboratory All are free

15 SM6LKM s VLF Receiver Runs on PC Just needs input from antenna/preamp Tunes 0-22 khz with mouse

16 Spectran

17 Spectrum Laboratory Complex and powerful program Plots spectrum view of signals received Allows reception for days in very narrow bandwidths

18 What is Earth-mode? Communicating through the ground via conduction/induction Signals attenuate very rapidly (inverse cube law)

19 Earth-mode Concept VLF signal injected into the ground or water Detected as a weak potential difference (or H field) at a distant point Conduction or induction? Some question theoretic explanations

20 Earth-mode Transmitter HF crystal/divider K1EL keyer IC TDA2003 5W PA VLF ATU

21 My Earth-mode Test Method Set TX running at home in CW or QRSS beacon mode into earth electrode antenna Check current in earth-electrode antenna Go out with /P antenna and PC Spectran or Spectrum Lab software used to find signal

22 2.5km on 0.838kHz 0.838kHz ULF signal at 2.5km strong!

23 5.1km on 8.76kHz

24 How far can you get? 6km so far with 5W QRP TX at 8.76kHz in 11mHz DSP filter River and sea coast DX tests planned

25 WSPR on 8.97kHz G6ALB received at 3km by WSPR (40W) Reception was possible with handheld E-field probe in upstairs shack

26 Help Needed More people looking for earth-mode signals in East Cambs area during tests More VLF grabbers needed for earth-mode and radiated DX reception More local earth-mode VLF TX beacons needed, running more power.

27 Radiated Sub-9kHz DX Equipment needed VLF/ULF reception (same kit as earth mode needed) RX possible without big antennas (E-field probe or small loop) Tuned preamp PC with suitable software (Spectrum Lab) Very accurate, GPS or similar LOCKED frequency setting VLF/ULF transmission Very stable, GPS locked, accurate frequency source High power AF amp with keyer + lowest loss matching Good insulators for kites and balloons Large earth electrode antenna, large loop or Marconi vertical

28 Radiated Sub-9kHz DX Stations active on radiated TX near 8.97kHz DF6NM DK7FC/P 648km* DJ8WX 645km* G3XIZ 45km* OE5ODL 1046km* OE3GHB OK2BVG PA3CPM Stations in yellow have been received in Burwell

29 Typical VLF TX station 100 to 300m high kite or Marconi antennas W from PA, 1-70mW radiated Ultra-stable GPS locked frequency source ATU with HUGE loading coils Some people are trying earth electrode and loop TX antennas

30 DK7FC s 8.97kHz Station Loading coil is HUGE Kite antenna up to 300m high Precise frequency is very important

31 DK7FC 8.97kHz Loading Coil Running 900mA antenna current into the beast Kilovolts at top of antenna 300m high antenna Dangerous!

32 DK7FC 8.97kHz Transmitter 600W PA using power MOSFETs

33 DK7FC s DX reports on 8.97kHz VLF with <100mW ERP

34 VLF signals seen at G3XBM khz signal received from DJ8WX (645km) this spring. Note timescale! kHz signal from G3XIZ (45km) on earth electrode RX antenna

35 UK Sub-9kHz Activity A few NoVs issued for 8.7 to 9.1kHz (100mW EIRP). Only needed for radiated tests. G3XIZ has spanned 160km on 8.97kHz BIG powers/antennas needed for radiated DX Radiated DX should be possible with large earth electrode antenna and QRO (G3XBM may try soon)

36 So finally. Simple kit can achieve results on VLF RX Lots happening on 8.97kHz only simple RX gear is needed. More info at s and any more questions?