> This is what I did to make a *USEFUL* "dip" circuit for
> my MFJ 259-B. Of course it should work with other
> RF generators too, but the MFJ (or equivalent) is
> hard to beat for convenience and reasonable accuracy.
In my opinion, there is NO "better way" to build a dip meter with an
antenna analyzer. The sensitivity will never be good.
The reason sensitivity is poor is because the coupling inductor has
very little current and very little external flux.
In a "real" dip meter, the inductor is part of an oscillator tank
circuit. The Q of that inductor is extremely high because the
inductor is part of a system with more feedback than loss (it is
oscillating). This means with even modest amounts of power the
magnetic field is very strong. Mutual coupling to any other circuit is
very high, because the field is intense.
(If you look at any formula for coupling, you will see Q is a strong
factor)
You can never do that with an inductor driven by an amplifier, and
the more resistors you add to the circuit the worse the problem
gets. I ran tests here, and the article in QST describes a system
that actually has less coupling and is less useful than simply
plugging an inductor right into the output jack of the antenna
analyzer!!!
Using an analyzer and a coil to make a dip meter is a very poor
system, it is usable only when the external system has reasonably
high Q and the coils are laid right against each other. That perturbs
the system you are measuring, and gives inaccurate results.
If you want a dip meter, buy a real dip meter. It will work a lot better.
73, Tom W8JI
W8JI@contesting.com
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