[R-390] R-390A balanced input question

[Charles Steinmetz]

>If you use the balanced input you can go through and trim up the 1st RF
>stages. Make sure you use the same hook-up that you are going to run with.
>    *   *   *
>If you use a balun (2.25:1 or 2:5:1) then you need to do the alignment
>through that connection. Make sure you set the ANT-TRIM knob to the center
>    *   *   *
>You are peaking performance. Usually I shoot for the middle of the band
>that is associated with that RF stage. Since I use one of the German-made
>baluns I do the  alignment from a 50 ohm unbalanced connection from my
>signal generator

That's all well and good, but there are only a few, very narrow 
frequency ranges between 500kHz and 32MHz at which the receiving 
antenna will be anywhere near 50 ohms.  So in the end, anything you 
can do with a 50 ohm generator isn't going to be very helpful because 
using a 50 ohm generator violates the first principle above, "Make 
sure you use the same hook-up that you are going to run with."

Instead, people with random antennas should ignore the balanced 
input, feed the unbalanced input, and ignore all the whining they've 
seen here and elsewhere about the unbalanced input "bypassing 
important tuned circuits."  All you're missing are the tuned 
primaries of T201-206 (depending on the band selected), and if you 
aren't matched to them (and the paragraph above explains why you 
won't be), you're much better off without them.  As a side benefit, 
the front end noise of the radio will usually drop significantly (how 
much depends on your particular antenna).

The only exception would be if you use an antenna tuner ("matchbox") 
to match a resonant antenna to 50 ohms, or if you cut an antenna 
specifically to be 50 ohms at some important frequency -- but this 
can only be true for very narrow frequency bands, because antenna 
resonances are very narrow.

Best regards,

Charles