tuner question...

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?

 

anyone?

 

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 .

 

thats interesting though, it makes some sense in a strange sort of way. Cheers toilette, twould be useful to know if anyone could express in lay - mans terms!

 

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.

 

thats great - mine are therefore currently incorrect...

 

normally the screw type connectors are for 300ohm and the coax sockets 75ohm...

you can use 75ohm into 300ohm but you need to bump the impedance up with a suitable balun .....[I think there calledthough I'm no expert ]

 

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.