Scott Hoffman writes in a message to All
  
 SH>  So what I'm using now is just a 300-->75 transofrmer and I'm 
 SH> inputting the 75Ohm into my scanner.. Does feeding the 75 Ohm 
 SH> input into the 50Ohm scanner input really make "that much" 
 SH> of a difference or is the difference pretty much minimul almost 
 SH> non-existant? 
  
There will be some loss because of the mismatch, but not enough to worry 
about.  What you should make sure of is that the antenna and transformer will 
pass all of the frequency bands that you are interested in.
  
The antenna should also have vertical elements - because 99% of the services 
that scanner hobbiests are interested in hearing are vertically polarized.  
If you have only horizontal elements and the signal is vertically polarized 
(it's like polaroid sunglasses that block horizontal glare) you might get 
1/10,000th (-40dB) of the signal that you would otherwise get.  In practice 
the null is never quite that deep, but it is there.
  
 SH> One last question.. Are antennas really 300 Ohms, I'm not sure 
 SH> I get this concept..
  
All signal sources have a charactaristic impedance which should be matched 
for best power transfer to the load.  The best you can do is to match the 
source and load impedances through a transmission line having the exact same 
charactaristic impedance.  An impedance is like a resistance, but in the case 
of a transmission line it is a complex capacitive/inductive/resistive 
relationship that describes how the line reacts when a signal is inserted 
into one end and taken out of the other.  No, I *don't* want to get into the 
math!  
  
 SH> Couldnt I just splice my low-loss RG-8 50Ohm cable right onto 
 SH> the antenna without even using a 300-->75/50Ohm transofrmer?
  
You could do that but it wouldn't be right!    What would happen would 
be a little like the standing mechanical waves on a musical instrument string 
with large signal amplitudes with out of phase current and voltage nodes 
inside the transmission line.  The signal would sort of bounce off the 300 
ohm/50 ohm line-to-antenna junction...  It ain't purty!  Suffice it to say 
that the 1.5 to 1 mismatch between the 75 ohm balun and the 50 ohm cable is a 
whole lot better than a 6 to 1 mismatch between 300 ohms and 50 ohms.
 
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