David,
As was said, it varies with the radio, but for an example, my old Yaesu
FT757 has a dual concentric knob. The inner knob tunes the center of the I.F
bandpass chanel without actually moving the receiver's frequency. So I tune
this knob to make the desired signal as loud as possible.

The outter knob is called, I think, Band width tuning. It moves the upper
and lower edges of the bandpass. Thus tuning it left, pulls the upper edge
of the bandpass down, decreasing the level of signals that re highter in 
frequency.
Moving this outter knov right pulls the lower frequency edge of the filter
up,thus cutting the level of lower frequency interfeering signals.

Other rigs work differently, some have a lower edge and seperate upper edge
adjustment on the two knobs.

Help any?

tom Fowle WA6IVG

On Sun, Nov 15, 2015 at 11:50:54PM -0500, David Pearson wrote:
> Hello all:
> 
> What is the proper method of adjusting twin passband tuning(two concentric 
> knobs) to isolate a desired signal on a receiverwith this function, and does 
> it work for all modes?
> 
> Thank you,
> 
> 
> 
> David S. Pearson-wa4dsp 
> 
> 
> ---
> This email has been checked for viruses by Avast antivirus software.
> http://www.avast.com