Colin,

The MFJ-212 tuner aid emits a pulsating noise through a directional coupler 
toward the tuner.  When the tuner is not adjusted to an SWR of 1:1., the 
pulsating noise is reflected back toward the receiver.  When the tuner is 
adjusted to an SWR approaching 1:1, the reflected noise decreases, a null, 
indicating the tuner is presenting a 1:1 or something approaching 1:1.  As 
was mentioned here by others, it may be necessary to reduce your RF gain and 
turn of your AGC to detect the pulsating noise.

If you do this carefully, and you have an amplifier, you should be able to 
tune your amp in to a dummy load, switch to the tuner and antenna and it is 
not necessary to put a signal on the air at all because you have already set 
your tuner to present a 50 ohm load to the amp.

73

Howard #3

---- Original Message ----- 
From: "Colin McDonald" <[log in to unmask]>
To: <[log in to unmask]>
Sent: Tuesday, September 03, 2013 3:14 PM
Subject: Re: Noise Bridge, clarification


> uhm, how does the 212 tune your tuner without transmitting a single
> milli-watt?
> Or is this simply marketting speak implying that your radio transmitter
> doesn't need to transmit any power?  I would suspect the 212 must have to
> transmit some rf to activate the tuner no?
>
> 73
> Colin, V A6BKX
> ----- Original Message ----- 
> From: "Jim Gammon" <[log in to unmask]>
> To: <[log in to unmask]>
> Sent: Tuesday, September 03, 2013 2:05 PM
> Subject: Noise Bridge, clarification
>
>
>> Howard, thanks much for the clarification here.  73, Jim
>>
>> ----- 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 14:46:16 -0500
>> Subject: Re: MFJ Noise Bridge: Another Question
>>
>> Jim,
>>
>> The MFJ-202B is not the same animal as the MFJ-212.
>>
>> The 202B MFJ RX Noise Bridge
>>
>> Quickly adjust almost any antenna for maximum performance, 1 to
>> 100 MHz.
>>
>> Lengthen or shorten your antenna for minimum SWR.  Measure
>> resonant
>> frequency, feedpoint resistance and reactance.
>>
>> Works with any receiver or transceiver.
>>
>> Hand-calibrated resistance scale, expanded capacitance range and
>> exclusive
>> built-in range extender.
>>
>> The MFJ 212 MatchMaker for Tuner
>> MFJ-212 Tunes up your antenna tuner without transmitting a single
>> milliwatt!
>> No power.  Precisely tune your antenna tuner for a 1:1 SWR -- no
>> additional
>> "tweaking" needed.  Avoids overheating/arcing caused by high SWR
>> and long
>> tune-ups.  MFJs RF*Guard bypasses the MFJ-212 to prevent damage.
>> Handles up
>> to 300 Watts.  Works with all radios 160-6 Meters.
>>
>> The 202B device is for adjusting antennas and the 212 is for
>> adjusting your
>> antenna tuner.
>>
>> 73
>>
>> Howard #3
>>
>> ----- Original Message -----
>> From: "Jim Gammon" <[log in to unmask]
>> To: <[log in to unmask]
>> Sent: Tuesday, September 03, 2013 12:38 PM
>> Subject: Re: MFJ Noise Bridge: Another Question
>>
>>
>> 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