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

Thanks to all for a very informative thread. You guys are living up
to your reputation.
Has anyone had any experience with an HP 8754? They seem to be
around, and with a b/w of 4-1300Mhz might be an excellent choice???
Darrell

Darrell, W4CX wrote:
"V/UHF is my priority since I`m building some copper loops for 6 and 2."

In the U.S., General Radio is champion. But, in Europe we used a British
Wayne Kerr UHF admittance bridge on lines and antennas in the middle of
a high frequency broadcast plant with a dozen or more competing
transmitters on the air at full power, as they always were.

The secret of success is the bridge detector used. A Collins 51-J was
useless, solid noise across the H-F bands. A Hammarlund SP-600 worked
like a champ.

Best regards, Richard Harrison, KB5WZI

On Fri, 27 Aug 2004 12:06:35 -0500, (Richard Harrison)
wrote:

Darrell, W4CX wrote:
"V/UHF is my priority since I`m building some copper loops for 6 and 2."

In the U.S., General Radio is champion. But, in Europe we used a British
Wayne Kerr UHF admittance bridge on lines and antennas in the middle of
a high frequency broadcast plant with a dozen or more competing
transmitters on the air at full power, as they always were.

The secret of success is the bridge detector used. A Collins 51-J was
useless, solid noise across the H-F bands. A Hammarlund SP-600 worked
like a champ.

Best regards, Richard Harrison, KB5WZI

Hi Richard,

Interesting you mentioned the Wayne Kerr UHF bridge. In my impedance-measuring
arsenal is the Wayne Kerr B108 admittance bridge. The beautiful aspect of this
bridge is that it's unknown terminals are balanced, thus allowing direct
measurement of balanced lines.

My arsenal also includes: 2 HP 8405 Vector Voltmeters with HP-778D dual
directional coupler.
HP-4815 Vector Impedance Meter
GR-1606A
GR-1606B
Boonton 250A Impedance Meter
PRD-219 Complex Reflection Coefficient Meter, 20 to 1000 MHz

What would you like me to measure?

Walt

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 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

I guess nobody just 'tunes for maximum smoke' any more

"Darrell Gordon W4CX" wrote in message
...
Group..I've just discovered this group (what took me so long?) and am
impressed with the knowledge here. I am shopping for an antenna
analyzer and am stymied by the choices (or lack thereof). In all of
hamdom (sub $600), I only find MFJ, Autek, AEA wireless, and Kuranishi
to choose from. I've checked eham reviews and found that the AEA VIA
(not Bravo) rates highest...and most expensive. Probably worth it.
Unfortunately, it's only good to 54Mhz, and I'd need up to 450Mhz. I
know this is impossible, and would be willing to go with separate
units (Autek), but they have awful reviews quality.

My question: What are you guys using for HF measurements? What about
V/UHF measurements? Do you recommend any particular model? How about
used HP gear from ebay (yes, I know the risks). V/UHF is my priority
since I'm building some copper loops for 6 and 2. What say you sage
antenna gurus?
Darrell W4CX



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And to think I've been tuning for minimum smoke all these years.
;^)

"Hal Rosser" wrote in message
.. .
I guess nobody just 'tunes for maximum smoke' any more

"Darrell Gordon W4CX" wrote in message
...
Group..I've just discovered this group (what took me so long?) and am
impressed with the knowledge here. I am shopping for an antenna
analyzer and am stymied by the choices (or lack thereof). In all of
hamdom (sub $600), I only find MFJ, Autek, AEA wireless, and Kuranishi
to choose from. I've checked eham reviews and found that the AEA VIA
(not Bravo) rates highest...and most expensive. Probably worth it.
Unfortunately, it's only good to 54Mhz, and I'd need up to 450Mhz. I
know this is impossible, and would be willing to go with separate
units (Autek), but they have awful reviews quality.

My question: What are you guys using for HF measurements? What about
V/UHF measurements? Do you recommend any particular model? How about
used HP gear from ebay (yes, I know the risks). V/UHF is my priority
since I'm building some copper loops for 6 and 2. What say you sage
antenna gurus?
Darrell W4CX



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Outgoing mail is certified Virus Free.
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My question: What are you guys using for HF measurements?

The original Autek. Limited accuracy,
but *very* portable and very useful.

I'm building the N2PK Vector Network
Analyzer, which is only good to 60Mhz,
with laboratory accuracy. Paul has hinted
at extensions to allow se to 450Mhz.
See www.n2pk.com .

The GR bridges suggested are very good,
but not too portable.

73, John - K6QQ