Build a aerial

[37831999]

How can i build a aerial capable of recieving tv signals and how do i amplify it using a car battery?

[beso]

If the signal is strong you can use a simple dipole. This utilises a pair of insulated elements spanning a quarter of a wavelength each. The wide side of the dipole faces the signal.

Find the frequency of the station and calculate its wavelength. Wavelength (metres) = 3*10^8 / frequency (Hz). Each arm of the dipole should be one quarter of the wavelength. If using a single dipole connect with 75 Ohm coaxial cable.

A folded dipole uses a folded conductor. You often see them made for FM radios from a piece of 300 ohm ribbon lead.

Cut a piece of ribbon to half the wavelength. Strip the conductors at the end and twist the two conductors together at each end. Cut one conductor in the middle and connect to the tv with another piece of ribbon. If the TV uses a coax input you needa "balun" to convert the lead impedance.

Simple dipoles work poorly with UHF because they pick up lots of reflections that cause ghosting.

Extra pairs of passive resonators are placed in front of and behind the dipole to increase directionality boost the signal and decrease ghosts.

Multi element TV aerials use either a log periodic or Yagi design. The Yagi gives the best results if you want a particular frequency or narrow range. The lower the frequency the larger the physical size. UHF band TV aerials are quite compact.

The directors of a Yagi are usually 95 percent of the length active dipole and the reflectors 105 percent. They are optimally spaced at one quarter wavelength in front and behind but this dimension is less important than the length.

Search yagi on Google to find a design calculator.

Masthead amplifiers are usually fed with a 24 volt DC supply from an AC adaptor but work fine at twelve volts. Just buy a normal mashead amp and bypass the AC adaptor.

[Teddio]

A thorough answer beso. You're not a radio amateur are you? I hope you get some thanks from the question setter!