> 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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