"Richard Clark" wrote in message
...
On Wed, 30 Mar 2005 08:16:42 GMT, "Jerry Martes"
wrote:

As you know, I built that slotted line that works fairly well for load
impedance measurements at 2 meters, and can be used at 100 MHz for FM
antenna work. But, it is big and ugly.

Hi Jerry,

Imagine how ugly it would be for 20M. You could use yours there too,
but you would have to study how to do what is called "load shifting."
Conceptually it is quite simple, but as you have learned, the art of
construction is where the accuracy is.

I do like the concept MFJ uses
even though the results are surely less accurate than a good bridge.

There are so many ways to lose accuracy that you should look at the
point spread. MFJ (and the other manufacturers) will probably suit
90% of users' expectations.

If I
get an urge to include a HF antenna or other device whose impedance I want
to determine, I might buy a MFJ. But, if a decent bridge ever becomes
available at one of the HAM swap meets I'll sure pick up anything thats
affordable.

Affordable generally runs in the neighborhood of $300. Myself, I
would invest in a swept frequency system that does vector analysis and
build heads that perform the SWR determination. This is
software/hardware at its best. Flexibility is the hallmark of an
instrument that will be kept being used.

73's
Richard Clark, KB7QHC


Richard

Your thoughts on sweep frequency for impedance measurement is very
interesting. If I could figure out a way to build the "sensors" I'd
probably build a sweep system for 2 meters. Although I could handle
building a sweep frequency generator, I wouldnt know how to convert the
"incident and reflected" to an impedance.
I suspect that, if sweep frequency impedance measurements was simple
enough for Me to do, someone would already have done it and published in one
of the HAM magazines.

Jerry

Jerry