"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

On Wed, 30 Mar 2005 14:45:12 GMT, "Jerry Martes"
wrote:

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.

Hi Jerry,

Quite simple. Radio Shack sells SWR meters for 2M so you can take a
lead for the sensors from there.

Although I could handle
building a sweep frequency generator, I wouldnt know how to convert the
"incident and reflected" to an impedance.

Software would do that.

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.

I'm sure that's already been done, at least in the ads in back. I am
NOT discussing what might be, but what has been done. There is a kit,
or kit design on the net, it's been mentioned here, I just haven't
rummaged up the link yet.

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Wed, 30 Mar 2005 14:45:12 GMT, "Jerry Martes"
wrote:

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.

The ARRL handbooks of yore have several designs. Google "monimatch".


Although I could handle
building a sweep frequency generator, I wouldnt know how to convert the
"incident and reflected" to an impedance.

Software would do that.

No it wouldn't, unless you could figure out some way to get vector magnitude
and phase from the two channels.


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.

Perhaps not the ham magazines; I know I've written at least three articles
in Kitplanes magazine as to how to do it for aircraft antenna VSWR.

Jim

On Wed, 30 Mar 2005 08:42:14 -0800, "RST Engineering"
wrote:

Although I could handle
building a sweep frequency generator, I wouldnt know how to convert the
"incident and reflected" to an impedance.

Software would do that.

No it wouldn't, unless you could figure out some way to get vector magnitude
and phase from the two channels.

Hi All,

I have since researched the archives to find my reference:
http://users.adelphia.net/~n2pk/

What can be done, what has been done, and what might be inferred is
revealed at this page.

73's
Richard Clark, KB7QHC

Richard

I'm way behind on the learning curve. I had read about that Vector
Network Analyzer last year. it looked too complicated for me to build.
And, in my ignorance, I thought that system was what the MFJ used.

The Smith Chart plots from his VNA data really impresses me. I could
possible get interested in building something like that for VHF, if I
understood it.

Jerry



"Richard Clark" wrote in message
...
On Wed, 30 Mar 2005 08:42:14 -0800, "RST Engineering"
wrote:

Although I could handle
building a sweep frequency generator, I wouldnt know how to convert the
"incident and reflected" to an impedance.

Software would do that.

No it wouldn't, unless you could figure out some way to get vector
magnitude
and phase from the two channels.

Hi All,

I have since researched the archives to find my reference:
http://users.adelphia.net/~n2pk/

What can be done, what has been done, and what might be inferred is
revealed at this page.

73's
Richard Clark, KB7QHC

On Wed, 30 Mar 2005 17:44:45 GMT, "Jerry Martes"
wrote:

The Smith Chart plots from his VNA data really impresses me. I could
possible get interested in building something like that for VHF, if I
understood it.

Hi Jerry,

Take the plunge, that is the best way to learn. You already exhibit
positive motivation and that's the hard part of learning.

73's
Richard Clark, KB7QHC

On Wed, 30 Mar 2005 09:19:40 -0800, Richard Clark
wrote:

[snip]

Hi All,

I have since researched the archives to find my reference:
http://users.adelphia.net/~n2pk/

What can be done, what has been done, and what might be inferred is
revealed at this page.

This is the greatest thing since sliced bread.

I've built one for ~$250.00. Here's a photo taken during construction
and checkout:

http://www.qsl.net/n7ws/ANA_1.jpg (350K)

Currently it's limited to 60 MHz although variants are in the works to
increase this. Another minor limitation is that the software is
DOS-based although Windows software is under development by other
users. Xp users, like me, have a couple of hoops to jump through to
access the parallel port but it's no big deal.

The accuracy, however, is lab quality and is comparable to commercial
network analyzers costing tens to hundreds of $K like I used to use,
although it's achieved at the expense of measurement speed.

Also see:

http://groups.yahoo.com/group/N2PK-VNA/

A higher cost alternative with much reduced dynamic range is he

http://radio.tentec.com/Amateur/vna

On Wed, 30 Mar 2005 11:15:41 -0700, Wes Stewart
wrote:

This is the greatest thing since sliced bread.

Hi Wes,

I can think of no greater commendation from an authority. Thanx for
the insights offered.

73's
Richard Clark, KB7QHC