The 212B is preset to 50 ohms and has only an off/on switch.  The 202 
requires adjustment so is harder for a blind person to use, but is 
more versatile.

73,

Dave, W7OQ

At 10:38 AM 9/3/2013, you wrote:
>How is the MFJ 212 different than the MFJ 202? I have one of the
>latter and there's no charger jack.  It only runs off the
>internal 9 VDC battery.  I hooked it up once to my receiver and
>tuned for a null but have no idea what kind of readings the knobs
>on the front may be giving me.  I assume there must be some
>numbers that correspond with the antenna resonance point or
>something.  Jim WA6EKS
>
>  ----- Original Message -----
>From: "Howard, W A 9 Y B W" <[log in to unmask]
>To: [log in to unmask]
>Date sent: Tue, 3 Sep 2013 11:17:32 -0500
>Subject: Re: MFJ Noise Bridge: Another Question
>
>Tom,
>
>I measured the polarity of the MFJ suggested wall wart that will
>work with
>the Noise Bridge and the center of the DC plug is positive as Pat
>indicated.
>
>73
>
>Howard #3
>
>----- Original Message -----
>From: "Tom Behler" <[log in to unmask]
>To: <[log in to unmask]
>Sent: Tuesday, September 03, 2013 8:34 AM
>Subject: MFJ Noise Bridge: Another Question
>
>
>  Hi, all.
>
>  I have another question about the MFJ Noise Bridge we have been
>  discussing.
>
>  I checked the MFJ web site, and found the MFJ 212 listed at a
>cost of $99,
>  which is what I expected.
>
>  They indicate that the device can be run either via a direct DC
>  connection,
>  or a wallwart power supply, which costs another $14.
>
>  Rather than spending the $14 on the extra wallwart, I'd rather
>run the
>  unit
>  off my rig runner via an Anderson Power Pole connection.
>
>  However, I'm not sure how the plug for the DC connection should
>be wired.
>  For example, is the tip positive?
>
>  In general, I'd be interested in how others on the list who have
>the noise
>  bridge power the unit.
>
>  Tom Behler: KB8TYJ