Johan SM6LKM has made available software to allow you to receive VLF transmissions, such as those by SAQ, using your PC soundcard.
SAQrx is a soundcard-based USB (Upper SideBand) receiver covering 0-22 kHz and the filter bandwidth is selectable in three steps, 300, 1000 and 2400 Hz.
The PDF file says to hook the antenna into the left channel of your soundcard input. It's in the block diagram in the PDF, but not documented anywhere else that I can find (except in the source code.)
To tune it, click and hold the area inside the blue and you can move it up and down the spectrum.
While not well documented, this is an amazing development and could lead to a much bigger development of a soundcard only for all bands.
What length of antenna would be required ?
I'm guessing the longer the better, but that may increase the chance of a static discharge into the sound card. Any ideas on a small bypass filter between the antenna and sound card. Maby a few parts from an AC wall outlet surge protectors filter circuit would work out got them in my junk box. Better to have some false security than none at all because I don't want my PC to be in the junk box.
This is a software defined radio using the soundcard as an A/D converter. SDRs require the sample rate of the A/D converter to be at least twice the frequency being detected. Regular soundcards top off around 96 or 48khz.
You might be able to use this as the detector of a superhet... just add an LO and a mixer... I might try this myself sometime.
You might also be interested in GNURadio. http://www.gnu.org/software/gnuradio/ It's capable of receiving all sorts of different modes and frequencies. To get those higher frequencies they use more expensive A/D converters though, not just a soundcard. It's also considerably more complicated. It's more of a toolkit that a programmer / RF engineer can use to create a radio.
Thanks! Fun! I've been playing with a couple of Rycom F selective volt meters, a Singer, and a Wandell and Goltermann I fixed. My effort was to hear the 600 meter guys but this is an interesting freebee.
Thanks again
EdZ KG6UTS
IT WORKS- AT MIDDAY I HEARD A VLF SIGNAL 8000 km AWAY.
Soundcard based Very Low Frequency VLF radio receiver.
The SAQrx Soundcard based Very Low Frequency VLF radio receiver with Panoramic tuning from 0 to 22 kHz works!!!!
I have long wanted a good 0 to 20 KHz receiver.
The computer software receiver works great.
The file size is a very small 48.0 KB so downloading is quick.
I use a 160 metre (1.8 MHz band) inverted V half wave dipole antenna.
I also tried a 20 metre (14 MHz band) inverted V half wave dipole antenna.
Both antennas use 50 ohm coaxial cable and work fine.
Connect the antenna into the computer microphone left input using a stereo 3.5mm plug.
Use the mouse to tune across the frequency display.
Click help on the downloaded display to find out how to use all the features including how to tune in 1 Hz steps!!!!
To give some protection to the computer microphone input I inserted a 175 ohm resistor in series with the antenna and 2 germanium diodes back to back between earth and the computer side of the resistor.
For better protection I disconnect the antenna from the computer when not needed.
On the 28 October 2008 at 0330 UTC (2.30pm Sydney afternoon) I heard
The Australian navy submarine broadcast station NWC North West Cape on 4 frequencies-
19.800 kHz
Signal strength was minus 60 db.
Displayed local oscillator frequency is 19.100 kHz.
The difference in frequency (19.800 minus 19.100 produces the 700 Hz audio).
18.600 kHz
Signal strength was also minus 60 db.
Displayed local oscillator frequency is 17.900 kHz.
20.500 kHz
Signal strength was minus 75 db.
Displayed local oscillator frequency is 19.800 kHz.
18.200 kHz
Signal strength was also minus 75 db.
Displayed local oscillator frequency is 17.500 kHz.
NWC North West Cape can be heard 24 hours over a distance of 3850 km from my home in Sydney on the east coast of Australia.
This is across land to the opposite side of the Australian continent on the West Australian coast in the middle of the day and at night.
The broadcast power of NWC North West Cape is 1 MW (1 megawatt, 1000 kW or one million Watts)
On 29 October 2008 at 0010 UTC all the above NWC North West Cape frequencies were absent.
The 19.800 kHz signal stopped at 0009 UTC and 18.600 kHz stopped at 0010 UTC. 18.600 KHz returned at 0017 UTC.
At 0100 UTC (midday in Sydney) I heard NPM, the U.S. Navy submarine broadcast station in Pearl Harbour, Lualualei, Oahu, Hawaii, USA on 21.400 kHz. Signal strength was minus 80 db.
Displayed local oscillator frequency is 20.700 kHz. This midday Very Low Frequency reception is a distance of 8175 km from Hawaii to Sydney, Australia.
They use 600 kW and can be heard in the day and night.
Listening to VLF above 20 kHz.
This year I have been listening from 20 kHz upwards using a Kenwood TS480HX transceiver.
The TS480HX clarifier allows the 30 kHz lower limit to be extended to receive down to 20 kHz with no modification.
Keep the TS480HX Preamplifier OFF as it blocks VLF signals between 20 kHz to 90 kHz.
I have enjoyed listening on the TS480HX from 20 kHz to 90 kHz to the Very Low Frequency Chinese and Japanese time signal stations and the US, Japanese and Australian navy submarine broadcast signals.
Now I have the 0 to 20 kHz missing link-
ULF Ultra Low Frequency 0 to 300 Hz
ELF Extremely Low Frequency 300 Hz to 3 kHz
VLF Very Low Frequency 3 kHz to 30 kHz (using this receiver plus the TH480HX above 20 kHz).
Listening to natural atmospheric, ionosphere, magnetosphere and solar-terrestrial interactive emissions is also a lot of fun in this part of the radio spectrum.
VLF amateur radio transceiver.
Now that I have this receiver I am thinking……. connect an audio signal generator to an antenna and make some contacts on the 4 kHz band?
0 to 9 KHz is the Somalia 100,000 metre amateur radio band.
It would be interesting to try the 100,000 metre band on the next holiday to Somalia. The small file size makes it easy to carry!
Maybe a similar matching Soundcard based Very Low Frequency VLF radio transmitter could make this a great ground wave transmitter transceiver that could be setup anywhere a computer can be found. That would save carrying the usual pile of equipment to overseas holiday destinations for VLF experimentation.
Swedish VLF morse code test transmission.
Radio station Grimeton, Sweden call sign SAQ is planned to be on air on Wednesday 24th December 2008 at 08.00 UTC and 08.15 UTC.
The frequency is 17.200 kHz CW.
Tuning of the transmitter begins about 07.30 UTC.
Click on the TUNE SAQ button on the SAQ VLF receiver and it will automatically put this receiver on 17.200 kHz ready to pickup the VLF morse code test broadcast from Sweden.
Thank you Johan SM6LKM for a great feature that everyone with a computer can enjoy.
I tried the program using 30 ft of speaker wire spliced to a 3.5mm plug and all I heard was noise. First I tried the antenna laid out streight and then I read on Wikipedia that it should be coiled so I tried that too and still just noise. No signals that I could make out.
A soundcard-based SAQ VLF receiver
Does this thing only pick up that one station?
Linear Mode
