Dear Roy:
Very interesting!
It just did not occur to me to test. Now that the EMC book I have
been helping with is finally being printed (over ten years in the
crafting) I shall put an appraisal of the AEA on our list of activities.
It occurs to me that almost all of my use of the instrument has been
below about 10 MHz. At those frequencies, my suspicions probably were
not tripped by a discrepancy of half a degree (or smaller).
I did buy the instrument after at least one change of hands.
Thank you very much for the heads-up. I am shaking my head in
wonder that that property I never thought to check.
Warm regards, Mac N8TT
--
J. Mc Laughlin - Michigan USA
Home:

"Roy Lewallen" wrote in message
...
A very capable engineering colleage of mine mentioned some time ago
that
an AEA he had purchased worked very well except for one thing -- the
reference point appeared to be inside the instrument. He said it was
as
though there were another length of line (about 5 cm as I recall)
inside. For example, measurement of a short circuit would indicate the
amount of positive reactance you'd expect from such a line. This might
not be too important for general purpose HF use, but would be a
problem
with some measurements, especially at high frequencies. It could be
removed by mathematical adjustment of the measurement results, of
course.

I mentioned this problem to the AEA folks at Dayton, not long after it
changed hands, and they might have fixed it. Do you see this
phenomenon?

I saw a similar thing when I spent a few minutes playing with the very
first model of Autek. I don't see this with my MFJ.

Again, the problem might have been fixed, but it's something to look
for, particularly on an older used unit.

Roy Lewallen, W7EL

J. McLaughlin wrote:

"Roy Lewallen" wrote in message
...
A very capable engineering colleage of mine mentioned some time ago
that
an AEA he had purchased worked very well except for one thing -- the
reference point appeared to be inside the instrument. He said it was
as
though there were another length of line (about 5 cm as I recall)
inside. For example, measurement of a short circuit would indicate the
amount of positive reactance you'd expect from such a line. This might
not be too important for general purpose HF use, but would be a
problem
with some measurements, especially at high frequencies. It could be
removed by mathematical adjustment of the measurement results, of
course.

I mentioned this problem to the AEA folks at Dayton, not long after it
changed hands, and they might have fixed it. Do you see this
phenomenon?

I saw a similar thing when I spent a few minutes playing with the very
first model of Autek. I don't see this with my MFJ.

Again, the problem might have been fixed, but it's something to look
for, particularly on an older used unit.

Dear Roy:
Very interesting!
It just did not occur to me to test. Now that the EMC book I have
been helping with is finally being printed (over ten years in the
crafting) I shall put an appraisal of the AEA on our list of activities.
It occurs to me that almost all of my use of the instrument has been
below about 10 MHz. At those frequencies, my suspicions probably were
not tripped by a discrepancy of half a degree (or smaller).
I did buy the instrument after at least one change of hands.
Thank you very much for the heads-up. I am shaking my head in
wonder that that property I never thought to check.
Warm regards, Mac N8TT


A few years ago, I was evaluating an AEA-CIA for a possible magazine
review. One of the tests involved a load consisting of some metres of 50
ohm coax terminated in three paralleled 50 ohm chip resistors. When the
frequency is swept, this load walks around the SWR=3 circle on a Smith
chart, giving |Z| values ranging between 16 ohms and 150 ohms with a
progressively rotating phase; or equivalent results in terms of
(R+/-jX). In other words, the test involves only moderately high or low
impedances with no nasty surprises.

The AEA-CIA gave good results as a frequency-sweeping SWR meter, and the
graphical display is unique in this price range; but unfortunately but
it did not give sensible results in the R-X mode (the mode that gives
the "Complex Impedance Analyser" its name). In a frequency range where
the true value of X was falling progressively through zero, the
indicated value came down correctly to about 30 ohms - and then suddenly
jumped to 0.0. The R readings continued to change with frequency exactly
as expected, but the X reading stayed 'stuck' at precisely 0.0 until the
sweep reached the frequency at which X changed sign, whereupon the X
readings started to make sense again. This behaviour was totally
reproducible. Also, the AEA-CIA is also supposed to be able to resolve
the sign of the complex impedance (which it presumably does by changing
frequency and noting what happens to X), but perhaps not surprisingly
this didn't work reliably either. At a constant frequency where the
value of X was nowhere close to zero, the instrument was often unable to
make up its mind about the correct sign.

All these symptoms looked like firmware problems to me. Since R and X
are both computed from the same analog voltage readings, and R was
correct while X was not, the problem had to be in the computation. The
AEA management at the time were quick to respond through the UK dealer.
They sent me schematics, and analog-type mods to try, and even replaced
the entire instrument... which behaved exactly like the one before.
However, they didn't seem to understand what I just wrote above, and
didn't want to go anywhere near the firmware.

In the end, I abandoned the effort and the UK dealer didn't import the
instrument. The magazine decided we should review the MFJ-269 instead -
which handled the same test load with good accuracy.

Sorry, I don't recall what specific firmware versions gave these
problems with the AEA-CIA, and have no information whether they have
been fixed in later versions. As Roy said:

the problem might have been fixed, but it's something to look
for, particularly on an older used unit.



--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Dear Ian:
Most interesting. Thanks.
I have not used the AEA-CIA for R-X measurements. I always assumed
that firmware was used to guess at the sign of X, and it is not too
surprising (though disappointing) that the chap who wrote the software
might blank out small values of X altogether. [In a spherical
navigation program that I wrote long ago for a slow computer, I flagged
results that would have been in the noise because of round-off error.
It took some effort to know when the results were bad. Others ignored
error analysis, being enamored of many random digits, with disastrous
results. Sometimes, with computers, no answer is the best one can do.
As an example: Cramer's rule just does not work to solve some systems of
linear equations using a computer! Even the HP48 uses an iterative
technique, which computers are real good at and people are not.]
The most interesting use that I made of the AEA-CIA, which would
have been difficult to do with a GR bridge, was measuring the apparent
surge impedance of a split boom to be used with a LPDA (prior to the
elements being attached). Leaving out the appropriate lectu I
terminated the split-boom with a series of resistors 'till the variation
in SWR (seen at the other end of the split-boom) with frequency was
minimal. [This is another example of SWR on a line depending on which
way one is looking.]

The strong suit of the AEA-CIA is in giving one repeatable data over
a wide frequency range. Most of the antennas that I deal with have
functional bandwidths of at least an octave. The value of the AEA-CIA
is much reduced if one is only interested in what is going on in a
narrow bandwidth.

Thanks very much for sharing your experience. We have once again
benefited from your experience and Roy's experience. 73 Mac N8TT
--
J. Mc Laughlin - Michigan USA
Home:

"Ian White, G3SEK" wrote in message
...
snip


A few years ago, I was evaluating an AEA-CIA for a possible magazine
review. One of the tests involved a load consisting of some metres of
50
ohm coax terminated in three paralleled 50 ohm chip resistors. When
the
frequency is swept, this load walks around the SWR=3 circle on a Smith
chart, giving |Z| values ranging between 16 ohms and 150 ohms with a
progressively rotating phase; or equivalent results in terms of
(R+/-jX). In other words, the test involves only moderately high or
low
impedances with no nasty surprises.

The AEA-CIA gave good results as a frequency-sweeping SWR meter, and
the
graphical display is unique in this price range; but unfortunately but
it did not give sensible results in the R-X mode (the mode that gives
the "Complex Impedance Analyser" its name). In a frequency range where
the true value of X was falling progressively through zero, the
indicated value came down correctly to about 30 ohms - and then
suddenly
jumped to 0.0. The R readings continued to change with frequency
exactly
as expected, but the X reading stayed 'stuck' at precisely 0.0 until
the
sweep reached the frequency at which X changed sign, whereupon the X
readings started to make sense again. This behaviour was totally
reproducible. Also, the AEA-CIA is also supposed to be able to resolve
the sign of the complex impedance (which it presumably does by
changing
frequency and noting what happens to X), but perhaps not surprisingly
this didn't work reliably either. At a constant frequency where the
value of X was nowhere close to zero, the instrument was often unable
to
make up its mind about the correct sign.

All these symptoms looked like firmware problems to me. Since R and X
are both computed from the same analog voltage readings, and R was
correct while X was not, the problem had to be in the computation. The
AEA management at the time were quick to respond through the UK
dealer.
They sent me schematics, and analog-type mods to try, and even
replaced
the entire instrument... which behaved exactly like the one before.
However, they didn't seem to understand what I just wrote above, and
didn't want to go anywhere near the firmware.

In the end, I abandoned the effort and the UK dealer didn't import the
instrument. The magazine decided we should review the MFJ-269
instead -
which handled the same test load with good accuracy.

Sorry, I don't recall what specific firmware versions gave these
problems with the AEA-CIA, and have no information whether they have
been fixed in later versions. As Roy said:

the problem might have been fixed, but it's something to look
for, particularly on an older used unit.

--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

J. McLaughlin wrote:
Most interesting. Thanks.

You're welcome. Just one small point, though:

I have not used the AEA-CIA for R-X measurements. I always assumed
that firmware was used to guess at the sign of X, and it is not too
surprising (though disappointing) that the chap who wrote the software
might blank out small values of X altogether.

In case anyone's not following this closely, I had been writing about
the AEA-CIA blanking out values of X less than about 30 ohms. That is
not "small" by any standard, and it only happened on one side of zero.
It could not possibly have been a deliberate feature of the programming.

In contrast, the MFJ-269 (and probably the 259B) does deliberately blank
out small values - truly small values, that is - as X passes through
zero. This occurs exactly as explained in the manual, and is exactly as
it should be.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

"Ian White, G3SEK" wrote in message
...
J. McLaughlin wrote:
Most interesting. Thanks.

You're welcome. Just one small point, though:

I have not used the AEA-CIA for R-X measurements. I always assumed
that firmware was used to guess at the sign of X, and it is not too
surprising (though disappointing) that the chap who wrote the software
might blank out small values of X altogether.

In case anyone's not following this closely, I had been writing about
the AEA-CIA blanking out values of X less than about 30 ohms. That is
not "small" by any standard, and it only happened on one side of zero.
It could not possibly have been a deliberate feature of the programming.

In contrast, the MFJ-269 (and probably the 259B) does deliberately blank
out small values - truly small values, that is - as X passes through
zero. This occurs exactly as explained in the manual, and is exactly as
it should be.
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

Ian, and others,

I have the 269 HF VHF UHF analyzer and noticed something strange. In
the "non-50 ohm" Advanced menu 3 mode, with the Zo set to 75 ohms, an
otherwise good 75 ohm load (please assume I know how to tell and I used a
low frequency to reduce errors) shows something like a 1.3 : 1 SWR. When I
called to ask about it, the first tech at MFJ seemed confused and clearly
did not understand. Another call, on another day resulted in a better tech,
but the response was to send it in for re-calibration. This also seems to
be a calculation rather than an adjustment, no?

Once you know Z it is a simple calculation to get to SWR for another Zo. Or
have I been smoking a bad brand...?

Woha! I see they have on line calibration manual for the 259B & 269 on
line!
http://www.mfjenterprises.com/MFJ-259Bcalibration.php
http://www.mfjenterprises.com/man/pd...alibration.pdf

I don't see anything other than "watch the blinking SWR" .(sounds like a
British insult) for the Advance 3 "calibration".

--
Steve N, K,9;d, c. i My email has no u's.

My MFJ 269 shows the SWR of a Tektronix 75 ohm termination as 1.0:1 up
to 77 MHz when Z0 is set to 75 ohms.

Roy Lewallen, W7EL

Steve Nosko wrote:

Ian, and others,

I have the 269 HF VHF UHF analyzer and noticed something strange. In
the "non-50 ohm" Advanced menu 3 mode, with the Zo set to 75 ohms, an
otherwise good 75 ohm load (please assume I know how to tell and I used a
low frequency to reduce errors) shows something like a 1.3 : 1 SWR. When I
called to ask about it, the first tech at MFJ seemed confused and clearly
did not understand. Another call, on another day resulted in a better tech,
but the response was to send it in for re-calibration. This also seems to
be a calculation rather than an adjustment, no?

Once you know Z it is a simple calculation to get to SWR for another Zo. Or
have I been smoking a bad brand...?

Woha! I see they have on line calibration manual for the 259B & 269 on
line!
http://www.mfjenterprises.com/MFJ-259Bcalibration.php
http://www.mfjenterprises.com/man/pd...alibration.pdf

I don't see anything other than "watch the blinking SWR" .(sounds like a
British insult) for the Advance 3 "calibration".

Thanks Roy. Mine shows it to measure 75 normally, but 1.3:1 in the Advanced
3 @75 ohms. Either I better change my brand of smokes or the Micro forgot
how to do the calculation... Better go back and try again to see it I
goofed somewhere...but I've done that several times...... . . . . .
.. .


Am I correct about this being simply a calculation?

--
Steve N, K,9;d, c. i My email has no u's.



"Roy Lewallen" wrote in message
...
My MFJ 269 shows the SWR of a Tektronix 75 ohm termination as 1.0:1 up
to 77 MHz when Z0 is set to 75 ohms.

Roy Lewallen, W7EL

Steve Nosko wrote:

Ian, and others,

I have the 269 HF VHF UHF analyzer and noticed something strange.
In
the "non-50 ohm" Advanced menu 3 mode, with the Zo set to 75 ohms, an
otherwise good 75 ohm load (please assume I know how to tell and I used
a
low frequency to reduce errors) shows something like a 1.3 : 1 SWR.
When I
called to ask about it, the first tech at MFJ seemed confused and
clearly
did not understand. Another call, on another day resulted in a better
tech,
but the response was to send it in for re-calibration. This also seems
to
be a calculation rather than an adjustment, no?

Once you know Z it is a simple calculation to get to SWR for another Zo.
Or
have I been smoking a bad brand...?

Woha! I see they have on line calibration manual for the 259B & 269 on
line!
http://www.mfjenterprises.com/MFJ-259Bcalibration.php
http://www.mfjenterprises.com/man/pd...alibration.pdf

I don't see anything other than "watch the blinking SWR" .(sounds like a
British insult) for the Advance 3 "calibration".

Steve Nosko wrote:

I have the 269 HF VHF UHF analyzer and noticed something strange.
In the "non-50 ohm" Advanced menu 3 mode, with the Zo set to 75 ohms,
an otherwise good 75 ohm load (please assume I know how to tell and I
used a low frequency to reduce errors) shows something like a 1.3 : 1
SWR.

And it had correctly showed SWR=1.5 when Zo was set to 50 ohms?

When I called to ask about it, the first tech at MFJ seemed confused
and clearly did not understand. Another call, on another day resulted
in a better tech, but the response was to send it in for
re-calibration. This also seems to be a calculation rather than an
adjustment, no?

Once you know Z it is a simple calculation to get to SWR for another
Zo. Or have I been smoking a bad brand...?

I didn't check this feature as part of the review, but it should be
simply the inverse ratio of whatever resistances you choose to define as
your Zo values.

Woha! I see they have on line calibration manual for the 259B & 269
on line!
http://www.mfjenterprises.com/MFJ-259Bcalibration.php
http://www.mfjenterprises.com/man/pd...alibration.pdf

I don't see anything other than "watch the blinking SWR" .(sounds like
a British insult) for the Advance 3 "calibration".

The MFJ-269 had to go back after the review (which itself was a few
years ago) so unfortunately I'm no longer able to check your findings,
Steve.

But don't recalibrate it yet, because that would be stirring-in
additional variables which will muddy the waters right now. After the
present question has been resolved, you may be able to give the
calibration procedure a little more TLC than there was time for on the
production-line - but you'll need some precision standards to do it.


--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

"Ian White, G3SEK" wrote in message
...
Steve Nosko wrote:

I have the 269 HF VHF UHF analyzer and noticed something strange.
In the "non-50 ohm" Advanced menu 3 mode, with the Zo set to 75 ohms,
an otherwise good 75 ohm load (please assume I know how to tell and I
used a low frequency to reduce errors) shows something like a 1.3 : 1
SWR.

And it had correctly showed SWR=1.5 when Zo was set to 50 ohms?

Yep! An extensive sheck of known good loads showed that the MFJ was
working as expected with reasonable accuracy. I don't have numbers, but 50
ohm loads looked ok and SWR, Z etc all appeared to be reasonable. Just this
one problem. (I have access to Agilent "N" cal kits)



When I called to ask about it, the first tech at MFJ seemed confused
and clearly did not understand. Another call, on another day resulted
in a better tech, but the response was to send it in for
re-calibration. This also seems to be a calculation rather than an
adjustment, no?

Once you know Z it is a simple calculation to get to SWR for another
Zo. Or have I been smoking a bad brand...?

I didn't check this feature as part of the review, but it should be
simply the inverse ratio of whatever resistances you choose to define as
your Zo values.

Woha! I see they have on line calibration manual for the 259B & 269
on line!
http://www.mfjenterprises.com/MFJ-259Bcalibration.php
http://www.mfjenterprises.com/man/pd...alibration.pdf

I don't see anything other than "watch the blinking SWR" .(sounds like
a British insult) for the Advance 3 "calibration".

The MFJ-269 had to go back after the review (which itself was a few
years ago) so unfortunately I'm no longer able to check your findings,
Steve.

But don't recalibrate it yet, because that would be stirring-in
additional variables which will muddy the waters right now. After the
present question has been resolved, you may be able to give the
calibration procedure a little more TLC than there was time for on the
production-line - but you'll need some precision standards to do it.
--
73 from Ian G3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek

The problem is the I found nothing wrong when measuring in all the other
modes. Only this one problem and I believe this is a calculation in the
microprocessor, not anything that can be "calibrated" to correct. I was
asking if this is correct. I also see nothing in the MFJ cal procedure for
the 269 for this mode other than "watch the blinkin' SWR symbol" (I
indicates you have set a Zo other than 50.
--
Steve N, K,9;d, c. i My email has no u's.