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[TowerTalk] Dipping with 259B and such

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Subject: [TowerTalk] Dipping with 259B and such
From: (Tom Rauch)
Date: Mon, 17 Sep 2001 08:08:57 -0400
> 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 

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 

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 

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