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

Walter Maxwell, W2DU listed an enviable collection of impedance
measuring devices. He`s prepared. Walter also wrote:
"In my impedance-measuring arsenal is the Wayne Kerr B108 admittance
bridge. The beautiful aspect of this bridge is that its unknown
terminals are balanced, thus allowing direct measurement of balanced
lines."

Yes. Balanced unknown terminals are convenient for a commercial
shortwave operator located away from the seashore. Horizontal wave
polarization with balanced feedlines is economical as compared with coax
for high power.

Unbalanced vertical antennas are convenient for groundwaves to extend
beyond the horizon for the mediumwave broadcaster. These antennas are
conveniently fed by coax of the concentric pipe or skeletal types. All
groundwaves are vertically polarized. These can travel very far at low
and medium frequencies. Attenuation of high frequency groundwaves is
severe. There is no propagation of horizontally polarized groundwaves at
all. The low-angle reflected wave is out of phase with the incident
wave.

Bottom line is that shortwave broadcasters transmit from horizontal
antennas and mediumwave broadcasters transmit from vertical antennas.
For shortwave, the target is reached via the ionosphere. For mediumwave,
the target is reached via the earth`s surface which is involved in
reaching beyond the line of sight.

For a dipole, you are likely to prefer a balanced bridge. For a
monopole, you are likely to prefer an unbalanced bridge.

Best regards, Richard Harrison, KB5WZI

"Richard Harrison" wrote -

There is no propagation of horizontally polarized groundwaves at
all. The low-angle reflected wave is out of phase with the incident
wave.

--------------------------------------------------------------

With a groundwaves there is no reflected wave and incident wave to get out
of phase with each other. By definition, it is all in the ground down to
one skin depth.

Very simply, a horizontally polarised groundwave, with its horizontal
current, suffers great attenuation in the loss resistance of the horizontal
ground. It gets launched but after one or two wavelengths it is many
decibels down.

This is the reason why horizontally polarised noise, relatively locally
generated, is smaller than the vertically polarised variety although, on the
average, both are randomly generated with equal amplitudes.

Half of the total noise power is dissipated in the ground except that which
is generated immediately adjacent to your receiving antenna.
----
Reg, G4FGQ

On Sun, 29 Aug 2004 09:31:13 +0000 (UTC), "Reg Edwards"
wrote:


"Richard Harrison" wrote -

There is no propagation of horizontally polarized groundwaves at
all. The low-angle reflected wave is out of phase with the incident
wave.

--------------------------------------------------------------

With a groundwaves there is no reflected wave and incident wave to get out
of phase with each other. By definition, it is all in the ground down to
one skin depth.

Reg, you are correct, of course, but Richard H. said above, "There is no
propagation of horizontally polarized groundwaves at all. The low-angle
reflected wave is out of phase with the incident wave."

What Richard mean't concerning the 'reflected' wave is that the energy radiated
downward from a horizontal antenna is reflected by the ground, and that
reflected wave is out of phase with the incident wave.

Walt, W2DU

On Sat, 28 Aug 2004 21:32:57 -0500, (Richard Harrison)
wrote:
snip
Unbalanced vertical antennas are convenient for groundwaves to extend
beyond the horizon for the mediumwave broadcaster. These antennas are
conveniently fed by coax of the concentric pipe or skeletal types. All
groundwaves are vertically polarized. These can travel very far at low
and medium frequencies. Attenuation of high frequency groundwaves is
severe. There is no propagation of horizontally polarized groundwaves at
all. The low-angle reflected wave is out of phase with the incident
wave.

Bottom line is that shortwave broadcasters transmit from horizontal
antennas and mediumwave broadcasters transmit from vertical antennas.
For shortwave, the target is reached via the ionosphere. For mediumwave,
the target is reached via the earth`s surface which is involved in
reaching beyond the line of sight.

Richard, when I was doing AM BC consulting more than 50 years ago I made the
observation from FCC ground-wave distance vs frequency propagation charts that
with the same ground conductivity and 1/4 wl antennas for both frequencies, the
1mv/m contour attained by 100 w at 540 kHz would require slightly less than 50
Kw at 1500 kHz,

Proves your point, doesn't it?

Walt, W2DU

Although a reflected horizontally polarized wave is out of phase with
the incident wave, and this explains the zero far field strength you get
with horizontally polarized waves, I'm not sure this is the relevant
explanation for the lack of ground wave propagation. The reason I doubt
it is that if you do the same analysis for vertically polarized waves,
you find that the net field strength is also zero at zero elevation
angle, except for the special case where ground is perfectly conducting.
So using the same analysis, you'd have to conclude that vertically
polarized waves can't propagate by ground wave, either.

Roy Lewallen, W7EL

Walter Maxwell wrote:
On Sun, 29 Aug 2004 09:31:13 +0000 (UTC), "Reg Edwards"
wrote:


"Richard Harrison" wrote -


There is no propagation of horizontally polarized groundwaves at
all. The low-angle reflected wave is out of phase with the incident
wave.


--------------------------------------------------------------

With a groundwaves there is no reflected wave and incident wave to get out
of phase with each other. By definition, it is all in the ground down to
one skin depth.


Reg, you are correct, of course, but Richard H. said above, "There is no
propagation of horizontally polarized groundwaves at all. The low-angle
reflected wave is out of phase with the incident wave."

What Richard mean't concerning the 'reflected' wave is that the energy radiated
downward from a horizontal antenna is reflected by the ground, and that
reflected wave is out of phase with the incident wave.

Walt, W2DU

Roy, W7EL wrote:
"So using the same analysis, you`d have to conclude that vertically
polarized waves can`t propagate by ground wave either."

I`ll turn to the authors for a source of my contention.

Terman says in his 1955 edition on page 803:
"The ground wave is vertically polarized, because any horizontal
component of electric field in contact with the earth is short-circuited
by the earth."

And on page 808, Terman says:
"Examination of these vector diagrams shows that with a perfect
reflector the horizontal components of electric field will exactly
cancel each other at the surface of the perfect conductor. In contrast,
the vertical components of the electric field of the incident and
reflected waves do not cancel, but rather add at the reflector surface
with small values of earth reflection angle."

Best regards, Richard Harrison, KB5WZI