I assume that you have already read SID VLF page and understood the main theme of a SID monitor. Here I will describe how to setup such a monitor in your home. The basic components of a SID monitoring station consists of antenna,receiver,preamplifier (sometimes it doesn’t need) & plotting and data processing software. See the block diagram given below:
There are several types of VLF antenna that could be used for our setup. A well-known VLF antenna is Magnetic loop. This antenna is sensitive in the magnetic part of an electromagnetic wave. It is widely used because it takes small space to mount comparing other VLF antennas. To make a Loop antenna see this page The problem of making a loop antenna is-it is expensive. You have to buy a lots of insulated copper wire and wound it around a wooden or plastic frame. My personal experience is not good with loop antenna. Lots of experiments are needed to get desired results. Another option is to make electric field (E-field) antenna. If you have enough space you can mount a long wire antenna or a HF half wave dipole antenna. But if you don’t have enough space to mount such big antennas you may mount a vertical long whip antenna. Follow the images below to get general idea about making antenna. There are lots of webpages on these antennas, so I recommend you to search in google for antenna making details. Remember don’t mount your antenna near any metal object & try to keep the antenna site free.
Preamplifier is needed to pre amplify the weak signals coming from the antenna. Generally a preamplifier should be low noise. This will help to get better performance. A simple and low noise preamplifier for the Loop antenna could be found here. A preamplifier may not always necessary to use. So if you want to avoid using preamplifier then you can skip this option.
Computer soundcard works as a VLF receiver. Because a typical soundcard can sample up to 48 KHz. Some high performance soundcard can sample up to 96 KHz. A typical soundcard is enough for our purpose. Connect your antenna to the line-in or microphone jack. If you use long wire antenna or long whip then connect it to the main wire of the line-in jack. For both cases ground your computer well. You can also ground the negative wire of the line-in jack. Then run your Computer and open recording devise manager. Now set the recording level to 100, turn off the boost option & set the sampling rate to 48000Hz. Follow the images below.
To monitor and plot the VLF stations you will need a FFT spectrogram software. The best spectrogram software is spectrum lab. Download it from here. Install it to your computer. Download this setting file, un-rar this & keep it to the hard disk. Now run the spectrum lab software. Then click File, choose Load settings from option and choose the setting file you downloaded to the hard-disk before. Click Ok. Now the new setting will begin its work. If your antenna successfully works then I hope you will see some VLF stations in the main spectrogram window of the software. Look at the image below.
In the above spectrogram we see five VLF stations; VTX1 from India, HWU from France and NWC from Australia, NDT from Japan, DHO38 from Germany. This result was found from my 10m dipole antenna without any preamplifier. A list of VLF transmitters could be downloaded from here.
If you receive any station then you are almost ready to monitor SID. Now you have to plot the signal strength of the received VLF stations. Go to View/windows > watch list & plot window. A window with multiple sub-window will appear. Follow these instruction images to configure the plotter. I don’t know how many stations you are receiving and you want to plot. So to configure the setting by your self, open the Watch List & plot windows option. Click to the memory, miscs (you can follow the instruction images) sub window. If you want to monitor one station then type 1 to the channels editing field > click the layout sub window & type 1 to the channels in upper part field > click the watch list > Here in the Title field type the station name you want to monitor> in the Expression field you have to put the frequency range you want to plot [avrg(min,max)]. Generally the difference between the min and max value may 100-150Hz. i.e If you want to monitor NWC at 19800 Hz then the min value may 19740 and the max value may 19860. Now open the plotter sub window > clickplotter > click run. The plotter will now run automatically. If you want to export the plotted graph values, go to the export sub window > here you will find something like this: C:\Spectrum\data\SL_VLF_RAW_DATA20121115.csv. Here 20121115 represent the Year month day. Edit it according to the new year month day information. This export option will automatically export and store the values in the c drive > spectrum > data folder for further analysis.