[R-390] Antenna question

[DCrespy@aol.com]

Whenever we get into these discussions, I cringe.  

We start sweating whether we have a 75 ohm or a 150 ohm antenna and feedline 
to match the balanced or unbalanced antenna connection on the radio.  Fact is 
for receiving with one antenna, we will be lucky at low frequencies to have a 
match for a few hundred kcs.  At higher frequencies we might get 500 kcs.  
Everywhere else the match will vary from a few ohms to a few thousand.   The 
coax impedance, does not correct for the antenna impedance.  In fact the 
radio sees the antenna impedance (I think they call this "conjugate 
matching").

The radio is wired (antenna to RF amp) for link (inductive) coupling for the 
"balanced input" and capacitive coupling for the "unbalanced input".  If I 
remember this right, theoretically, you should get better dynamic range with 
the "balanced" and better tolerance of mismatches through the "unbalanced".  
That is the only real difference.  I'd just be sure to decide which you plan 
to use and use that connection for alignment.  Otherwise it really shouldn't 
matter much.  I think Chuck Ripple has some data that overall performance is 
better using link coupling.

Finally, pick the feedline for best isolation from noise, not for impedance.  
RG-6 is very good with a foil shield.  The twisted pair discussion also seems 
a good solution.

Finally and unrelated, if enough of us are hams, would there be any interest 
in an R-390 net some time?

Enough for tonight!

73
Harry  KG5LO


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