We have considered the frequency band up to about 40 KHz; the spectrum is that represented in the image below, obtained with the SDR application. Among the various emissions, we have identified three VLF transmitters that can do for us : this is the All these broadcasters are mainly used for radio communications with submarines, since VLF waves can penetrate many meters below the surface of the sea.
The The following maps show the location of the three selected VLF transmitters. The chart below has been recorded at This graph shows signal strength against time over a 24 hour period. It shows random variation in signal strength at night, followed by a change decrease as the rising sun recreates the D-layer.
During the day, signal strength varies with the altitude of the Sun. At sunset, the D-layer recombines and is lost, producing another change increase in signal strength. Unfortunately our environment and our homes are saturated with electromagnetic disturbances and we have to live with. The main four flares can be identified.
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Abstract: in this post we describe the application of the SMA Thunder Optics spectrometer and the Spectragryph software to the spectroscopic analysis of the pigments responsible for the photosynthetic process, pigments found in all plant organisms plants and algae. The combination of the low-and bandpass-filter supresses the unwanted military data signal rests passing the IF filter in a sufficient way.
The last stage is made with a LM , a very cheap audio amplifier circuit, to drive a small loudspeaker. The circuit can be built in metal or even plastic enclosures.
The following picture shows some suggestions. The left receiver was installed into a common Hammond die cast enclosure. The receiver in the middle was built in an old PC loudspeaker housing and the right one was made using a cheap ABS enclosure.
It is not necessary to create a PCB, a hole grid board like shown below or even an ugly bug is ok. The only important thing is to take care about proper grounding all over the circuit to avoid oscillaton. An aluminium foil below will reduce the capacitive effects caused by the human hand while holding the receiver.
In the compact receiver a coil of a few hundred turns of 30SWG enameled copper wire is wound on to a paper bobbin and set on to the ferrite rod. The antenna road is fixed to the circuit board which has a suitable multi-way connector on the other end. See the layout diagram below. The whole is assembled inside a waterproof plastic tube with suitable ends as shown in the sketch below. The actual antenna and circuit board are shown assembled as below.
The polar response of the completed receiver was plotted with the equipment mounted on a large protractor as shown below. One of the strong VLF transmitters was used as the signal source. Its amplitude was measured as a function of antenna rotation. The measurement procedure was almost identical to that for a large loop antenna which is described in the file. A typical dipolar response diagram is shown below.
AC Circuit Theory. David Morgan, 11 Feb , EM Induction. David Morgan, 12 Feb , Join the YouTube channel of the Alexanderson Association and decide for yourself if it might be an exciting experience to listen to Grimeton Radio on You just need the antenna for half an hour two times a year, so clamp a wooden holder for an active antenna e-field probe into your shack window see Fig.
If you want to build a simple antenna by your own, try this example for a homebrew active antenna. When mountig the e-field probe on a pole in the garden, let the cable touch the ground before it reaches your sound card or even establish a galvanic contact to the ground.
Maybe you want to try a ferrite rod antenna. Our ancestors used it with great effort for long wave reception.
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