Production of HF wave detector (electronic and radio waves)

This detector will allow you to verify the presence of radio waves emitted by the devices that surround us (cell phones GSM, WiFi routers, ...) as well as energy leaks to high-frequency
the door of the microwave oven ...

Principle:

Radio waves are emitted by varying electric current in a rapidly antenna (alternating current of a certain frequency).
A simple electrical wire, placed at a distance, can capture those variations in current, but with an amplitude decreasing rapidly with distance.
When the power of a transmitter is high (more than 10 watts), one can easily turn a light bulb to less than 10 cm ...!
For low power (less than 1 watt for mobile phones), it is more sensitive detectors, but these are generally polarized (equipped with + / - signs), and it will transform the
AC rectified current, using a diode ...

Realisation:

 

Assembly with only few components, it can be done on
a simple copper plate of bakelite, on which we will have three grooves etched
insulation with a knife:

Welding of the diode

 

As with all CMS components, tin the first plan
copper to one side of the diode, Using tweezers, remove the
diode on the tin, and cook quickly with a soldering iron
(Allow 1 to 2 seconds), the first side is welded. It only remains to be welded
the other side ... not that complicated! [For desoldering, in case of error or
recovery, simply reload the welding electrodes of the 2 component, and
maintain these two hot junctions alternately passing the soldering iron
from one side to the other, then push the component with the tip of the iron
due course. ]

Test

We manufacture a dipole with two fortune copper strands directly
soldered to the PCB. For best reception, the length
total dipole must be equal to half a wavelength.
Here are some values ​​of wavelengths found by applying the
formula L (m) = 300 / F (MHz):
L = 33 cm for 900 MHz GSM
L = 16 cm for GSM at 1.8 GHz
L = 12.5 cm for WiFi,
Bluetooth, or microwave oven, sending all three of 2.4 GHz.
Respectively half-wave antennas of about 16 cm, 8 cm and 6
cm. The prototype used in this article uses an 8-cm dipole,
achieving a compromise to detect three frequencies, and try some
experiences ...

With a GSM phone

 

Simply place the sensor at 5 cm from the mobile phone, and dial
the 123 to call your email (free) to observe the effects
a transmission with pulse phase (reception only) and
periods of full power when it comes to opinions ... talkative!
With a microwave oven
The received signal level similar to that of a GSM phone, in
Walking the detector 5 to 10 cm in front of the oven door. We
noticed a difference signal variation when a glass of water
is placed at the edge or the center of the turntable. The needle deflects to
full scale if the oven is idle (not recommended). We will find the
signal reflection, approaching a metal device (toaster,
stainless steel sink ...) placed in the path of the waves ...

With WiFi

 

The received signal level is more difficult to capture if network activity is
low. This gives a good deflection by connecting to a stream
Internet TV (such as NASA TV) ...
Your turn ...!
By imagining gain antennas, circularly polarized, reflector
parabolic, or cavities filter ... to gain directivity in
sensitivity and selectivity, in order to try to catch the relays GSM
located on the terraces of buildings!