Looking for a cheap, small piece of equipment that can detect radio waves within a home, or office space. Don't know what that is called or where to find one. Its for a science experiment. I want to actually be able to measure radio waves, intensity etc on a graph or scale. to see what in the house creates more or stronger radio waves. Need the name and where to buy one. For what frequency range and what power level?
You could easily tune your AM radio into an unused frequency and pickup random noise emitted by fluorescent light bulbs, etc. Or, you could take an audio amplifier, connect it to a loop made of wires, a diode, and pickup all sorts of magnetic waves.
Edit:
OK... now the details are there... what you want is an equipment called a spectrum analyzer. Don't bother trying to buy one as they are 50,000 dollars and higher. There is no cheap device you can buy for this purpose.
The spectrum that you are looking for are from 60Hz to several hundred mega-hertz. The only way I can think of doing is something like this:
Take an amplifier, such as your stereo with a VU meter. Connect a shielded wire to the input of this amplifier. At the end of it, make 10 turn loop with insulated wire, and to one end, connect a diode. 1N34 or 1N60 available from radioshack will be fine. Direction of this doesn't matter. Then connect the whole thing to the end of the shielded wire. To recap... end of the shielded wire, the center goes to one lead of the diode. The other lead goes to the coil. The other side of the coil goes to the shield of the wire.
What you are making is a quick and simple magnetic pickup. You know, radio waves are partly magnetic waves. You are trying to pick it up. As you come close to house wires, you will hear BUZZzzzz.... As you come close to a television, you will hear another Buzzz..... You could look at the VU meter to guestimate the strength.
It won't be accurate but this is probably the best you can do. Scanner (go to radio shack) It is easy to build yourself. Take a germanium diode and an antenna and a 1MegOhm resistor. The resistor should be connected to the banded end of the diode to chassis ground.
The telescopic antenna is hooked up to the unbanded end of the diode and the banded end is connected to an audio amplifier input like either phono or auxillary or CD. The amplifier should, must have a ground return to earth... like in a three prong AC plug. That is - the amplifier chassis has to be grounded. There is usually a screw on the metal back to tie up a wire.
There may be a problem with using a diode..... They don't conduct unless the input voltage has reached 150mV for germanium diodes or .6V or 600mV for silicon diodes. They work fine for any signal above their respective threshold voltages. There is a way around it though - the diodes have to be negatively biased to Just the threshold voltage. Then they will conduct at the slightest signal. Are you up to that? To sum up - with no biasing diodes the ambient spectrum must be higher than the threshold voltages of the diodes..... otherwise the receiver will be quiet.
If you can afford an FFT (Fast Fourier Transform) spectrum analyzer - which are very expensive - unless you get one on eBay very cheap - is even better. It shows you the spectrum of all the frequencies with their respective amplitudes. I have quite a few of those.... all different ranges. The FFTs are usually for the lower frequency spectrum like audio and LF - while the swept IF ones are for radio frequencies from Long waves up to Plenty of Giga Hertz.
EDIT:
I am afraid that the recommendation of my friend above needs some clarification. Regarding the pick-up coil (if you use one), depending on the frequency band that has to be detected, that coil has to have many thousands of windings for lower frequencies like 60Hz. The coils I use for that have 40.000 windings with various taps. Further - the coil should have a soft iron or a ferrite core. Then one gets a decent output that will bridge the threshold voltage of the germanium diode like the 1N 34 or 1N60.
The less windings a coil has or the lower the inductance the coil has, the lower is the pick-up level and the higher the detectable band. The output of the coil will then drop down to milli- or microvolts. You have to experiment. Remember - we are dealing here with the inverse square law of EMF field radiation/strength. Let's say 1meter from the source is the reference level of 1. 2 meters distance diminishes the field strength to 1/2; 3meter = 1/9th; 4 meter = 1/16th; 5meters = 1/25th etc of the field strength.
To bias the diodes: get a 500kOhm potentiometer and a 1.5V battery. Connect both outer tabs of the control to the battery terminals. The wiper (middle tab) is connected to a 100kOhm resistor. The + terminal of the battery is connected to ground/Chassis. The free end of the 100kOhm resistor is connected to the amplifier input... where the banded end of the germanium diode also goes. Adjusting the control will give you a good setting so the threshold voltage of the diode is overcome and she conducts instantly..... or you may adjust the sensitivity as required.
Electronic hobbyist... technician |
