At 01:04 PM 8/29/2005, RLVZ@aol.com wrote:
>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.
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.
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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