Michael Coslo wrote:
wrote:


The 4170 makes this a lot easier as you can measure the feedline actual
parameters as well as calibrate out their effects.


This is a dumb question on my part, but what you are saying is that the
mitigating effects that the cable has on the VSWR, making it look better
in general, can not only be calculated and "calibrated out", but that
the actual SWR of your antenna at the feedpoint is then given?

As you get closer to 1.1:1 at the actual antenna, would accuracy then
suffer? If feedline loss can bring an antenna that is not near that to a
level approaching that, wouldn't it mean that teh calibration is
somewhere in the noise?

Like I say, this could be a really stoopid question.

- 73 de Mike N3LI -

Basically what you do is calibrate the instrument at the measurement
point, whether that point is the instrument connector or at the end of
a length of coax.

You attach an open, a short and a known resistance; 50 ohms by default
but it is user definable.

The instrument than frequency sweeps and stores the results in a user
definable calibration file.

When you make a measurement of an unknown, you define which calibration
file to use and the instrument corrects the readings to display the
characteristics at the measurement point.

Given that this is a $500 insturment and not a $20,000 labratory instrument
there are going to be limits to how accurate all this is.

After having used the AIM for a while, my opinion is that it far execeeds
what is required for practical amateur usage.

If you want to see some actual numbers, you can find a comparison of the
results of an AIM 4170 compared to HP lab equiment at:

http://www.bnk.com/w0qe/AIM4170_page1.html


--
Jim Pennino

Remove .spam.sux to reply.

..
snip

Basically what you do is calibrate the instrument at the measurement
point, whether that point is the instrument connector or at the end of
a length of coax.

You attach an open, a short and a known resistance; 50 ohms by default
but it is user definable.

The instrument than frequency sweeps and stores the results in a user
definable calibration file.

When you make a measurement of an unknown, you define which calibration
file to use and the instrument corrects the readings to display the
characteristics at the measurement point.

Given that this is a $500 insturment and not a $20,000 labratory
instrument
there are going to be limits to how accurate all this is.

When I inspected antennas, we had two multi-kilobuck "Site Master"
instruments from Anritsu, mentioned here, that had a set of calibrated
terminations. IIRC, to calibrate the unit(s), we had to connect the
terminations, a short, a 50-ohm resistor and a shielded open circuit, one at
a time, to the instrument and tell it which one was connected. It swept the
frequencies of interest and stored its own baseline behavior over that band
of interest. Then, anything connected to it was referenced to that
baseline. We could also store a range of sweep frequencies (usually by the
name or type of antenna we intended to sweep) and it would recall all the
parameters. Automated, repeatable sweep testing is not available (yet) in
lower cost instruments.

I presume we could have calibrated any given cable, too. (Never required by
our test memos.)

Sal

Sal M. Onella wrote:
.
snip
Basically what you do is calibrate the instrument at the measurement
point, whether that point is the instrument connector or at the end of
a length of coax.

You attach an open, a short and a known resistance; 50 ohms by default
but it is user definable.

The instrument than frequency sweeps and stores the results in a user
definable calibration file.

When you make a measurement of an unknown, you define which calibration
file to use and the instrument corrects the readings to display the
characteristics at the measurement point.

Given that this is a $500 insturment and not a $20,000 labratory
instrument
there are going to be limits to how accurate all this is.

When I inspected antennas, we had two multi-kilobuck "Site Master"
instruments from Anritsu, mentioned here, that had a set of calibrated
terminations. IIRC, to calibrate the unit(s), we had to connect the
terminations, a short, a 50-ohm resistor and a shielded open circuit, one at
a time, to the instrument and tell it which one was connected. It swept the
frequencies of interest and stored its own baseline behavior over that band
of interest. Then, anything connected to it was referenced to that
baseline. We could also store a range of sweep frequencies (usually by the
name or type of antenna we intended to sweep) and it would recall all the
parameters. Automated, repeatable sweep testing is not available (yet) in
lower cost instruments.


The $600 TenTec/TAPR VNA does open/short/thru/load calibration with
sweeps, etc. I don't have the AIM, but I'll bet it does too. These
days, it's not a big deal to include it.

"Jim Lux" wrote in message
...
Sal M. Onella wrote:
.
snip
Basically what you do is calibrate the instrument at the measurement
point, whether that point is the instrument connector or at the end of
a length of coax.

You attach an open, a short and a known resistance; 50 ohms by default
but it is user definable.

The instrument than frequency sweeps and stores the results in a user
definable calibration file.

When you make a measurement of an unknown, you define which calibration
file to use and the instrument corrects the readings to display the
characteristics at the measurement point.

Given that this is a $500 insturment and not a $20,000 labratory
instrument
there are going to be limits to how accurate all this is.

When I inspected antennas, we had two multi-kilobuck "Site Master"
instruments from Anritsu, mentioned here, that had a set of calibrated
terminations. IIRC, to calibrate the unit(s), we had to connect the
terminations, a short, a 50-ohm resistor and a shielded open circuit,
one at
a time, to the instrument and tell it which one was connected. It swept
the
frequencies of interest and stored its own baseline behavior over that
band
of interest. Then, anything connected to it was referenced to that
baseline. We could also store a range of sweep frequencies (usually by
the
name or type of antenna we intended to sweep) and it would recall all
the
parameters. Automated, repeatable sweep testing is not available (yet)
in
lower cost instruments.


The $600 TenTec/TAPR VNA does open/short/thru/load calibration with
sweeps, etc. I don't have the AIM, but I'll bet it does too. These
days, it's not a big deal to include it.




Thanks for bringing me into the present.

I have an analyzer already. When I drop it off the roof (inevitable), I
will look at the TenTec/TAPR VNA.