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Re: [TowerTalk] How to get "50 ohms J Zero"?

Subject: Re: [TowerTalk] How to get "50 ohms J Zero"?
From: Jim Lux <>
Date: Mon, 29 Aug 2005 16:22:13 -0700
List-post: <>
At 01:04 PM 8/29/2005, wrote:
>Hi Guys,
>Please advise what instruments can be used to adjust an antenna for  "50 ohms
>J Zero"?  I believe the MFJ 259B may do it but don't know how  accurate it
>is.  Are there precision instruments that can be purchased  used?  If so, 
>advise name of manufacturer and model  number.
>Thank You!!!
>Dick- K9OM

How precisely do you need to adjust it?

The MFJ is accurate enough for almost all ham work.

If you need gnat's eyelash precision, then things like calibration 
standards will be important. A good short is easy to come by. A decent 50 
ohm load is not too hard. A really good open at HF is quite difficult 
(fringing fields, etc.).

The various kinds of measurement methods mostly differ in how much of the 
calibration work is "inside the box".  It IS possible to make very precise 
impedance measurements with a set of standards, a fairly grungy detector, 
and a decent voltmeter, but it's a lot of work. (as in, more than it's worth).

You can probably find a decent RF impedance bridge used for several hundred 
dollars.  The HP vector voltmeters are a nice way to approach the problem, too.

Jim, W6RMK


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