Microwave Radiometer Homebuilt With Low Cost Components and Easy Availability

Abstract:

This essay is a source of inspiration for anyone who wants to build a microwave radiometer at home at a cost of 70 Euros.

http://giammaiot.blogspot.it/2015/12/microwave-rad...

Summary:

This essay is cause for inspiration to anyone who wants to build a microwave radiometer at home and at a cost of 70 Euros.

For the assembly of this instrument we were used:

- System with CBL probe voltage( voltmeter datalogger )

- Satfinder analog hand (tool for pointing satellite dishes)

- LNB (Low Noise Block = low noise amplifier)

- Connection cables

- AC or battery pack

Keywords and concepts of interest:

- CBL System ( datalogger system )

- Radiant energy Tools of radiometry and spectrometry

- Telecommunications

- Radioastronomy

1. Introduction

After reading a few articles appeared on the Internet I wanted to play a very interesting project that is worth analyzing.For a small fee you can interface the CBL [CBL = Computer Based Laboratory is an interface for graphing calculators Texas that allows easy and economical data collection in real time] to a kit for research and tracking satellite television. This application turns cbl in a microwave radiometer, an instrument capable of detecting the radiant energy of electromagnetic waves characterized by high frequency (GHz), and short wavelength (order of 1 - 1000 mm, inverse proportionality lambda = 1 / f).The study of this type of waves is complex and bound to the theory of black body.This theory provides that any body at temperature T greater than 0 ° K, is a source of electromagnetic radiation. The same body, when it is hit by electromagnetic radiation, it absorbs a part and reflects the remainder. The motion of thermal motion of atoms and molecules is responsible for irradiation of electromagnetic energy (which comes at the expense of thermal energy); conversely, the absorption of radiation, when there are no other energy exchanges, entails an increase of the thermal energy. If the body temperature is kept constant is provided a dynamic equilibrium such that the emitted energy and the load absorbed by the body in unit time are equal. From the phenomenological point of view, and in practice, it appears that the radiation emitted by a hot body depends not only on its temperature, but also by other factors such as the geometry and the type of the material.Not only heat waves travel on these frequencies, but also satellite transmissions, lines wi-fi of many electronic devices, cellular transmissions, microwave, domestic, radar, and many other devices.Many objects emit, absorb and / or reflect the radiant energy in the form of microwaves. Even living beings, celestial bodies and thermal reactions of various origin (chemical, physical or biological) are subject to this phenomenon.Studies have shown that the growth of some plants (Swiss Stone Pine, Larix decidua) is somewhat related to the cyclical nature of the density of sunspots, detectable precisely through the use of a microwave radiometer as a radio telescope.It should also be said that these waves can be both harmless (the temperature of a body at 37 degrees, the radio frequency signal, the solar light) that are harmful to living beings (mobile phones, radio links, sunlamps). Such harmfulness is given as well as the high power and intensity with which they are transmitted, the frequency and duration of exposure.

Fig. 1 electromagnetic spectrum

2. Methodology and assembly

The system is realized by connecting a low noise amplifier (LBN) to a satfinder (instrument for the pointing of the satellite dishes), modified to be interfaced to the CBL, and using a power supply at 12/20 Volt. The cost of the system is about 70 euro excluding CBL.

The analysis for the realization of the circuit should be made according to certain parameters:

- Voltage limit CBL: -10 V to +10 V

- The actual voltage supplied to the analogue pointer of satfinder, that will determine our sensitivity.

- The analog will be connected to the voltage probe CBL

- The LNB supply that varies from model to model

- Feeding satfinder (compatible with that LNB)

First there must be effective to change the satfinder, soldering two wires to the poles of the analog gauge. The voltage probe of the CBL will measure this potential difference (Fig 4. Modify SatFinder).

1. Connector for LNB

2. Alternate connector for the power supply of the satfinder at 12/20 Volt.

3. Original connector (used for power if you do not make the point 2)

4. Welds on the pins of the analog gauge

5. Output, to be connected to the probe CBL We arrange to provide a power wire, connected to the input of the satfinder, suitably adapted to the needs of the connectors and polarity. Otherwise, as in the picture we provide to provide an alternative connection to the power supply (Figure 4 low-cost model can be found easily on the internet).

Finally we connect the input connector satfinder LNB (Fig 5. Assembled system).

For security, you can enter a suitable impedance block 10 mH inserted between the positive supply and the cable supplying the satfinder.

3. Data collection

You can make radiometric measurements of various sources: here are some examples.

A. Mobile phone, incoming call: sampling was done every millisecond to five seconds.

Fig 6. Graph radiant energy.

B. Emissions from a cell tower: sampling was done every millisecond to five seconds.

Fig 7. Graph radiant energy.

C. Turn on and off a light bulb: sampling was done every millisecond to five seconds.

Fig 8. Graph radiant energy.

4. Conclusion

We have seen how, with little expense, we can investigate in the microwave.In this paper we were presented some examples that suggest the multiple applications of this tool created mainly for amateur use in chemistry, biology, astronomy, meteorology, telecommunications.To give a scientific meaning to the data available, we should adopt a reliable calibration procedure.

Bibliography

[0] My Blog - GiamMa-based researchers SDR R&D IoT

http://giammaiot.blogspot.it/2015/12/microwave-rad...

[1] A microwave radiometer for only 50 EUR:

www.iaragroup.org/scuoleeassociazioni/labuniverso/...

[2] Implementation human microwave emission device:

www.crit.rai.it/eletel/2006-2/62-1.htm

[3] Radiometro a microonde interfacciato al CBL:

http://ulisse.sissa.it/biblioteca/saggio/2007/Ubib...