Home |
Search |
Today's Posts |
|
Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
Reply |
|
LinkBack | Thread Tools | Display Modes |
#1
Posted to sci.electronics.repair
|
|||
|
|||
diy uhf TV antenna
hi there,am tinkering with an old tv and would like to learn more about antennas,& try with different shapes. what i would like to understand before starting is if an antenna is basically a closed loop of wire shorting the inner pole and outer poles on the RF out on the back of the tv what should the resistance of this loop be in total? or is it an open loop? thx |
#2
Posted to sci.electronics.repair
|
|||
|
|||
diy uhf TV antenna
1 beerismy:
There is most likely NO RF out on the back of the TV.... it is probably an antenna or RF INPUT. If it is a "F" type coaxiall jack the nominal impedance will be 75 ohms, if you have two screws for the antenna or RF input, the nominal impedance will likely be 300 ohms. Note that the impedance is NOT the same as DC resistance like you would measure with your multimeter. A simple UHF antenna could be a stiff wire loop of about 7 inches in diameter. This will have a DC resistance of near ZERO ohms but an impedance of about 300 ohms at UHF frequencies so if you are connecting it to a 75 ohm input jack you will need a 300 / 75 ohm balun matching transformer for best performance. electricitym .. .. .. |
#3
Posted to sci.electronics.repair
|
|||
|
|||
diy uhf TV antenna
Andy replies:
Get a copy of the ARRL handbook or, even better, the ARRL Antenna Handbook... You have a lot of getting up to speed to do before you will actually accomplish anything. Once you understand the basics, you can do almost anything with coat hangers. Otherwise, you will only create bent up wires that may or may not work at some frequencies and not at others... It ain't black magic --- antenna design has very definite rules and they are not difficult. It's a lot like hanging sheet rock. If you understand what you are doing, it is easy. If you don't , you have a mess.... good luck... We all started just the way you are now. You may find that it is a hell of a lot of fun. Or you may decide, "the hell with it". But there's no reason for "trial and error" when the actual discipline is very methodical and reasonable....... about the complexity as changing the oil in your new truck for the first time.... Andy W4OAH |
#4
Posted to sci.electronics.repair
|
|||
|
|||
diy uhf TV antenna
|
#6
Posted to sci.electronics.repair
|
|||
|
|||
diy uhf TV antenna
|
#7
Posted to sci.electronics.repair
|
|||
|
|||
diy uhf TV antenna
i have read a bit more on this and have successfully created a simple
dipole which gets VHF & some UHF too.my favorite channels come in with no snow, but with some ghosting. i read that raising the dipole in the sky would cure it but would require building a tower. would adding a reflector help with this? i read that a dipole's reflector is a piece of wire a bit longer than the diapole. would it make any difference if i get more drastic and use a rectangle of foil or chicken mesh to block out everything coming from behind the diapole? thx |
#8
Posted to sci.electronics.repair
|
|||
|
|||
diy uhf TV antenna
|
Reply |
Thread Tools | Search this Thread |
Display Modes | |
|
|
Similar Threads | ||||
Thread | Forum | |||
ANTENNA CONNECTOR ID | Electronics Repair | |||
Making FM Dipole Antenna | Electronics Repair | |||
Telescopic antenna repair | Electronics Repair | |||
Modified CB antenna for Scanner | Electronics Repair | |||
Microwave interferes with AM radio | Home Repair |