I recently got myself a noise bridge to do some quantitative measurements on
my antennas.
Lets say I am a bit disappointed. The small dials of the unit make all my
antennas to appear very similar indeed and I am wondering if the unit is
broken (not according to the test I did with a known load) or if I am
expecting way too much.

What do real people use to do impedance measurements on their antennas (
and please do not suggest anything from MFJ).


73

Uwe

Uwe

I'd like to hear more about MFJ, and why you dont want to hear more about
them. I was thinking that they were a pretty good way of measuring
impedance.

Jerry



"Jaggy Taggy" wrote in message
...
I recently got myself a noise bridge to do some quantitative measurements
on
my antennas.
Lets say I am a bit disappointed. The small dials of the unit make all my
antennas to appear very similar indeed and I am wondering if the unit is
broken (not according to the test I did with a known load) or if I am
expecting way too much.

What do real people use to do impedance measurements on their antennas (
and please do not suggest anything from MFJ).


73

Uwe

I agree with Jerry. Why not use an MFJ. I have two of their oldest
units one for HF and one VHF, the models 207 & 208. Bought mine a long
time before he put the to measuring devices together. They measure the
resonant freq. and that is what you want to know right? Mine have
worked fine for years and still do. His newer instruments are just
great. Wish I could justify buying the new MFJ-259B. I had the chance
to play with one and it is terrific. If you can't determin everything
about your antenna with that, well, you are just a lost soul in a techie
world. Friends still will borrow one or the other of my ancient units to
check their new construction or to find how far off their antennas have
become from the original design. MFJ makes affordable, accurate, devices
for Hams and as long as Martin F. Jue is running the place they allways
will.

Butch Magee KF5DE
Diamondhead, MS

Jerry Martes wrote:
Uwe

I'd like to hear more about MFJ, and why you dont want to hear more about
them. I was thinking that they were a pretty good way of measuring
impedance.

Jerry



"Jaggy Taggy" wrote in message
...

I recently got myself a noise bridge to do some quantitative measurements
on
my antennas.
Lets say I am a bit disappointed. The small dials of the unit make all my
antennas to appear very similar indeed and I am wondering if the unit is
broken (not according to the test I did with a known load) or if I am
expecting way too much.

What do real people use to do impedance measurements on their antennas (
and please do not suggest anything from MFJ).


73

Uwe

On Wed, 30 Mar 2005 00:48:17 GMT, Jaggy Taggy
wrote:

I recently got myself a noise bridge to do some quantitative measurements on
my antennas.
Lets say I am a bit disappointed. The small dials of the unit make all my
antennas to appear very similar indeed and I am wondering if the unit is
broken (not according to the test I did with a known load) or if I am
expecting way too much.

Hi Uwe,

The Cadillac of Bridges is the General Radio 1606-A. However, it
requires you to have a source and detector. It is only a Bridge, but
it is a precision Bridge. The circuit is quite simple, but its triple
shielding and isolation are old-world craftsmanship. These things
sold at a price equivalent to 6 months wage for a bench tech. 6
months wages currently will buy you equipment that could do what was
only possible in a standards lab back then - but this is still in the
region of 5 figures.

You will need a stable source capable of 1 to 10mW power. You will
need a well shielded communications receiver to act as a detector.
You will also need a steady hand to balance the bridge (which may be
part of your problem with the noise bridge). Nulls are often more
than 100 dB deep. If you lack sufficient shielding for the detector,
this will degrade the nulls considerably. If you lack stability, you
will never find the null.

The MFJs of the world are quick and dirty, but when they reach their
limits you can only guess because they will as easily feed you a bogus
reading when they are out to lunch. The GR 1606 has limits too, but
they are obvious by dial indication and a top end of 60MHz usage (a
more practical top end, however, is 30MHz).

73's
Richard Clark, KB7QHC

"Richard Clark" wrote in message
...
On Wed, 30 Mar 2005 00:48:17 GMT, Jaggy Taggy
wrote:

I recently got myself a noise bridge to do some quantitative measurements
on
my antennas.
Lets say I am a bit disappointed. The small dials of the unit make all my
antennas to appear very similar indeed and I am wondering if the unit is
broken (not according to the test I did with a known load) or if I am
expecting way too much.

Hi Uwe,

The Cadillac of Bridges is the General Radio 1606-A. However, it
requires you to have a source and detector. It is only a Bridge, but
it is a precision Bridge. The circuit is quite simple, but its triple
shielding and isolation are old-world craftsmanship. These things
sold at a price equivalent to 6 months wage for a bench tech. 6
months wages currently will buy you equipment that could do what was
only possible in a standards lab back then - but this is still in the
region of 5 figures.

You will need a stable source capable of 1 to 10mW power. You will
need a well shielded communications receiver to act as a detector.
You will also need a steady hand to balance the bridge (which may be
part of your problem with the noise bridge). Nulls are often more
than 100 dB deep. If you lack sufficient shielding for the detector,
this will degrade the nulls considerably. If you lack stability, you
will never find the null.

The MFJs of the world are quick and dirty, but when they reach their
limits you can only guess because they will as easily feed you a bogus
reading when they are out to lunch. The GR 1606 has limits too, but
they are obvious by dial indication and a top end of 60MHz usage (a
more practical top end, however, is 30MHz).

73's
Richard Clark, KB7QHC


Richard

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. I do like the concept MFJ uses
even though the results are surely less accurate than a good bridge. 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.
I am impressed that computer programs seem to have made impedance
*measurement* unnecessary to most HAMS. I sure wish I was enough smarter
to be able to manipulate the computer so I could get confidant about
computer program results. That really impresses me when I read about how
accurately antenna impedance can be predicted for various changes in
parameters.

When you guys arent argueing about stuff I cant understand, I sure learn
alot from this Antenna Group.

Thanks
Jerry

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 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

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.

A pick-up loop will do the same thing for ladder-line.
--
73, Cecil http://www.qsl.net/w5dxp


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"Cecil Moore" wrote in message
...
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.

A pick-up loop will do the same thing for ladder-line.
--
73, Cecil http://www.qsl.net/w5dxp



Cecil

I've always ignored the use of twin lead for impedance measurement. But,
it makes sense. I may try building something like that, just for fun.

I certainly havent thought this "twin lead" line thru but it seems that
one could be easily built from a length of PVC pipe with wires attached to
its sides.
This seems too easy and relatively accurate for "home in the garage" use.
I'd bet I can find some info on the Internet for FM and TV frequency use.
Thanks for jogging my mind.

Jerry