4^BST – Liceo Scientifico Tecnologico I.T.I.S. Italo Calvino di Genova Sestri Ponente

1. How it’s possible to make a radio link by transmitting an extremely low power(without any electromagnetic hazard) 4^BST – Liceo Scientifico Tecnologico I.T.I.S. Italo Calvino di Genova Sestri Ponente April 2005 I.T.I.S. Italo Calvino, via Borzoli 21, 16153 Genova Sestri Ponente Tel. 010-6504672, Fax 010-6504241, e-mail: istituto@calvino.ge.it

2. Index • Goal • How the project was born • The experiment • The theory • On Monte Gazzo • The experimental results • Conclusions • Acnowledgments • Some photos

3. Goal We show that it is possible to establish a 2-km radio link by transmitting only few nanowatts

4. How the project was born -Our school, with the help of University and other Italian Secondary Schools, is developing some educational modules in order to keep the attention of young students to radiocommunications topics. -After reading: Radio transmissions (radiotransmissions.doc) and: A simple approach to radio transmissions(englishradiocom.ppt) we made a radio transmissions experiment.

5. The experiment - The experiment was aimed to: -measure the sensitivity of a radio receiver; -verify how the transmitted and the received power are related; -estimate the minimum transmitting power to receive a well audible signal at a distance of 2 km; -show that it is possible to establish a radio link by using very low power.

6. The sensitivity of our receiver FM Receiver Radiofrequency Signal source -We connected a FM receiver (operating at 433 MHz) to a radiofrequency small signal source: -We heard a well audible signal with a radiofrequency power of only PR = 10-11,4 mW = 4 10-15 W (a very low value!) NOTE: we learned the decibel: –114 dBm = 10-11,4 mW (they are strange, but easy!)

7. The radiotransmission system RX power meter (spectrum analyzer) Cable (13 m) Replaced after the 1st test with the FM receiver Antenna (Effective area: 0.76 m2) Receiver subsystem (on M. Gazzo) distance r = 1800 m Transmitter subsystem (ITIS Calvino) Antenna (Gain: 20) Replaced after the 2nd test with low power radiofrequency source Wattmeter Transmitter 433 MHz 4 W Cable (7m)

8. The cable loss -The output power PO of a cable is proportional to the input one PI, i.e. PO = K PI, then K = PO/PIand K < 1. - With an input power of PI = 4.7 W to the 7 m cable we measured an output power PO = 3.3 W, then the cable used in the transmitter subsystem had K1 = 3.3 / 4.7 = 0.70. - With an input power of PI = 4.7 W to the 13 m cable we measured an output power PO = 2.65 W, then the cable used in the receiver subsystem had K1 = 2.65 / 4.7 = 0.56.

9. Some theory before the experiment - The TX output power before the experiment was: Ptx = 3,9 W - According to the 7 m cable loss, the expected input power to the TX antenna had to be: Pt = K1 Ptx = 0,7 3,9 = 2,73 W - Since the antenna gain was G = 20, its Equivalent Isotropic Radiated Power had to be: EIRP = G Pt = 20  2,73 = 54,6 W - At distance r = 1800 m, the area of a sphere centered to the TX antenna had to be A = 4 p r2 = 4  p  18002 = 40,7  106 m2 - The power flux density on the RX antenna had to be: S = EIRP / A = 54,6 / (40,7  106) = 1,34 10-6 W - The output power from the RX antenna (whose effective area is Ar = 0,76 m2) had to be: Pr = Ar  S = 0,76  1,34 10-6 = 1,02  10-6 W - According to the 13 m cable loss, we expected a RX power: Prx = K2 Pr = 0,56 1,02  10-6 = 0,57  10-6 W

10. The experiment on Monte Gazzo - We went to Monte Gazzo. Our school was well visible and the line of sight joining our school seemed well free from obstacles. - The transmitted power from ITIS Calvino was Ptx = 3,9 W - The received power from M. Gazzo was Prx = 10-3,2 mW = 0,63 10-6 W Considering reflections, diffractions, interferences, errors associated to the instruments… …we obtained a good result! (NOTE: we expected 0,57  10-6 W).

11. How much power for communications? - By transmitting 3.9 W we received a power enormously larger than the minimum value that was necessary to hear a well audible signal: 0.63 10-6 W VS only 4 10-15 W - What is the minimum value of the transmission power? We apply the following simple rule: Ptx: Prx = Ptx min: Prx min then: 3.9 : 0.63  10-6= Ptx min: 4 10-15 we obtain: Ptx min= 3.9 4 10-15/ 0.63  10-6= 25  10-9 W The communications should be possible by using only: 25  10-9watts! We want to verify this result…

12. Let’s try to transmit only 25 nW -We replaced: - the transmitter with a radiofrequency source (that is able to generate a very low power) - the spectrum analyzer with a FM receiver. with only 25 nW the audio signal was well audible (and with 15 nW the signal was discernible)

13. Radiocommunications are possible… …without electromagnetic hazards! - 25 nW radiated by an antenna having a gain of 20 are equivalent to: 500  10-9(one half millionth) watt EIRP - At what distance from the TX antenna is the power flux density greater than 0,1 W/m2? (maximum value allowed in Italy for constant human exposure) - We obtain 0,63 mm, but this result has not sense since the short distance from the antenna. In this case there is no any electromagnetic hazard!

14. Conclusions - We approached the telecommunications world (we also learned the meaning of decibel!). - We found out important relations between science and technology and … …we showed how its possible to establish a radio link (over a considerable distance) without any electromagnetic hazard (and interpreted “electrosmog” topics in a more realistic way).

15. Future works - Our work was mainly based on energetic aspects. - We are interested to know the electromagnetic waves properties.

16. Acknowledgments Many thanks to: - Our teachers Mr. Giuseppe Olivieri and Ms. Marina Ravera, for their scientifc support. - Mr. Alessandro Iscra and Mr. Claudio Novelli, for organization. - Ms. Maria Teresa Quaglini, for her technical support.

17. Some photos

18. We were here! Monte Gazzo form I.T.I.S. Calvino

19. Our school is here! Our school from Monte Gazzo

20. Monte Gazzo The small square at M. Gazzo Our school The two points connected