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[TowerTalk] Re: Dipping with 259B and such

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Subject: [TowerTalk] Re: Dipping with 259B and such
From: (Tom Rauch)
Date: Mon, 17 Sep 2001 15:50:48 -0400
> Actually, the 259B is *NOT* used as a grid dip meter in this
> application...the external meter is the "dip" indicator and
> it really is quite sensitive. Perhaps I didn't make that clear.  

The 259B has a detector right across the output port that 
measures voltage there, as well as a detector that measures 
current in series with the output port (which is what the described 
detector measures), and the display will clearly reflect changes as 
small as one bit out of 256 bits (0.4%) change in current and/or 

With an external detector, all we can do is measure the very same 
parameters. It is no different than what is already inside the unit.

The problem is the lack of mutual coupling, nothing else. That 
problem can not be cured unless the coupling coil is part of a 
system that is resonant with high levels of regeneration.

Understand I am not saying it doesn't work, just that the system 
will always lack the high mutual coupling that exists when the dip 
coil is part of an oscillating tank circuit. 

While there are better form factors and inductance values for one 
application or another (which may, in a given test, make one 
system behave better than another), overall the system has many 
times less sensitivity than a regular dip meter. 

> BTW, MFJ sells a set of 2 plug-in coils for the 259.  It's
> called a "Dip Meter Adapter"  Model MFJ-66.  I found that
> item to be absolutely worthless for "grid dip" applications.

Ironically, assuming the are built and used correctly, the MFJ coils  
are more sensitive than the adapters described in QST for equal 
diameter coils!! I'm positive of that.
73, Tom W8JI 

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