How to make a simple radiotransmission by using a videorecorder and a TV-receiver Luisa Bove, I.T.I.S. Caramuel, Vigevano (Pv) Alessandro Iscra, I.I.S. Deambrosis–Natta, Sestri Lev. (Ge) Giuseppina Rossi, Liceo Cairoli, Pavia (Pv) November 2005

The videorecorder and the TV-receiver Tipically, a videorecorder can be connected to a TV-receiver in 3 different ways: -By using the SCART cable -By using audio/video cables or similars -Between the coaxial antenna cable. Power cable Scart(s) Female coax connector (from antenna) Male coax connector (radiofrequency from VCR to TV) Typical rear side of a VCR

The connection with the coaxial cable When the connection is realized between the coaxial cable, the videorecorder emulates a TV transmitter and feeds the cable with a radiofrequency signal. Rear side of TV Coaxial cable

Lets transmit via the coaxial cable Lets disconnect all cables from our videorecorder, with the only exception of the coaxial cable between the VCR and the TV- receiver (and, obviously, the power cable). Lets set up the VCR for playing a cassette. Lets tune the TV-receiver on the VCR transmitted channel. Now the TV-receiver is receiving the VCR radiofrequency signal.

Lets cut the cable After creating or buying another very cheap coaxial cable, we may cut it and obtain (by stripping) two small dipole antennas. Now we can see that the TV-receiver receives with a wireless connection. Rear side of TV Suggested length: /4

Some experiments According to the very low power transmitted by the VCR, we can make: - Several experiments on polarization; -Some experiments on transmissions through several objects; -Antennas with better performances.

A little problem The received signal might be corrupted by a signal radiated by a near TV transmitter. In this case it is necessary to tune first the TV receiver and then the VCR on a new RF channel (see your manuals).

Channels and frequencies Videorecorders grenerate signals in the Ultra High Frequency band (UHF). Frequencies are related to a channel identifier N that varies between 21 and 69. The frequency associated to the video signal is: f V = (N – 21) × 8 MHz. The frequency associated to the audio signal is: f a = f V MHz.

Warnings Since the VCR and the TV-receiver are supplied by 230 V, dont touch antenna conductors. Radiotransmissions are regulated by severe laws. Dont connect amplifiers between the VCR and the transmitting antenna.