what is the difference between a 75 ohm and 300 ohm aerial? i have a large dedicated aerial outdoors for my two tuner leak troughline and an old sansui - I have to connect an aerial socket, by two pieces of wire to the tuners by screws- which should I use and why? whats the difference?
tuner question...
- Thread starter banpe2006
- Start date
la toilette
Downright stupid
Well I can quote my 70's Marantz receiver manual to you, it may help.....
"The best FM reception is obtained with a Log-Periodic type antenna mounted on a good quality rotor system. For fringe areas Marantz recommends a Log-Periodic antenna with six or more elements designed expressly for FM reception. To minimise local noise and multipath picked up by the lead-in wires, use a balanced and shielded 300 ohm cable or coaxial 75 ohm cable witha 300 to 75 ohm matching transformer at the antenna. Unshielded lead-in acts as an omnidirectional antenna, and can cancel the directional benefits of your antenna. Low-loss 300ohm shielded cable consists of two inner conductors plus an outer shield and insulating jacket. This type of shielded cable effectively prevents the lead-in from contributing multipath distortion."
Then it rattles on about rural areas and the use of 300ohm 'Rabbit ear' antennas, and lastly.....:
"If 75ohm cable is desired, we recommend using the type with an "F" Type connector terminal attached".
There you go, clear as mud
.
"The best FM reception is obtained with a Log-Periodic type antenna mounted on a good quality rotor system. For fringe areas Marantz recommends a Log-Periodic antenna with six or more elements designed expressly for FM reception. To minimise local noise and multipath picked up by the lead-in wires, use a balanced and shielded 300 ohm cable or coaxial 75 ohm cable witha 300 to 75 ohm matching transformer at the antenna. Unshielded lead-in acts as an omnidirectional antenna, and can cancel the directional benefits of your antenna. Low-loss 300ohm shielded cable consists of two inner conductors plus an outer shield and insulating jacket. This type of shielded cable effectively prevents the lead-in from contributing multipath distortion."
Then it rattles on about rural areas and the use of 300ohm 'Rabbit ear' antennas, and lastly.....:
"If 75ohm cable is desired, we recommend using the type with an "F" Type connector terminal attached".
There you go, clear as mud
.
It's an RF impedance-matching thing. When correctly matched, the tuner sees a much stronger input signal.
If you have a roof/loft-mounted aerial using a coaxial download , to a wall-mounted socket perahps, it should be plugged into the 75ohm input.
If you have one of those nasty T-shaped tape-to-the-wall wire-type 'aerials' it should be connected to the 300ohm input.
Either will work in the 'wrong' input, but you'll give up signal strength.
If you have a roof/loft-mounted aerial using a coaxial download , to a wall-mounted socket perahps, it should be plugged into the 75ohm input.
If you have one of those nasty T-shaped tape-to-the-wall wire-type 'aerials' it should be connected to the 300ohm input.
Either will work in the 'wrong' input, but you'll give up signal strength.
both of my "antique" tuners have 3 screws on the back and no aerial socket...there are 2 screws for 300 ohm and 1 for 75 ohm...I have attached 2 pieces of wire to an external aerial socket (ie the socket that would usually sit in the casework of a modern tuner, is outside the case attached to the two outer screws (300ohms) by wire that I soldered to the points on the socket...(does this make any sense?) as i have 2 pieces of wire - where do they go? On the back of the tuners there are 2 screws for 300ohm and only 1 screw for the 75 ohm - why is this and how do I now use 2 pieces of wire on 1 screw? I have an outdoor dedicated fm aerial that is huge! so it should get good reception in our very poor area.
