Re robust designs. There is also a powerful inertia effect. If you make
a new probe that gives different results, what happens about 'pass'
decisions made using the old probes? You wouldn't want to make problems
for the customers, would you? Many of the outline testing networks in
CISPR 16-1 are 'hands-off' because of this, even though some are very
vintage indeed.
John Woodgate OOO-Own Opinions Only
J M Woodgate and Associates www.woodjohn.uk
Rayleigh, Essex UK
On 2018-03-07 14:52, Patrick wrote:
Hello Ed -
Great story- thanks for sharing!
Just last year, we had a broken sensor head on a HI-6053.
It was built circa 2015, so it would be considered a "modern" probe.
I did the same as you and took it apart - it was already broken, so
nothing to lose!
(how many of us have been doing that since we were kids!)
The description you give of the "old" probe matches exactly what I
found inside the HI6053.
Dimensions were a bit different, and electronics are in a square box.
But the basic design of sensor and high impedance connecting cables
are the same!
I guess some designs are robust enough to survive for decades.
Thanks again for the story.
BTW- thanks also for yesterday's story about the evolution of our
industry.
It reminds me that what we think is "settled" is really just the
boundary of our understanding.
And, as our understanding grows then those boundaries move too.
Always great to hear your perspective!
Thank you !
On Tue, Mar 6, 2018 at 2:57 PM, Edward Price <[email protected]
<mailto:[email protected]>> wrote:
*Patrick:*
**
*The probe manufacturer says something like “keep the probe box
away or out of the field” or “best results are obtained with the
probe placed on a slant.” But then they show us isotropicity data
that promises +/- ¼ dB. It seems like those are contradictory
statements.*
*Back around 2002, I decided to dissect a dead Narda 8762(?) probe
which a customer helped me drop. The Narda was a white Fiberglas,
300 MHz to 1 GHz probe that looked like a very elegant German
“potato masher” hand grenade equipped with a cable that plugged
into an IFI EFS field sensor. I wish I had taken some good
pictures of the project, as few people venture that deep into such
expensive territory.*
*The head contained the orthogonal three-dipole array, with the
conductive arms looking like gold foil on a thin Fiberglass
substrate. The length of each dipole was about 1.5 inches. The
sensing elements might have been thermocouples, thermistors or
diodes, and they were mounted in the dipoles. Each sensor was also
connected to a pair of very high resistance plastic wires
(possibly doped with carbon like automotive spark plug wires) that
ran to the far end of the stalk where an analog signal
conditioning amplifier summed the three channels and provided a DC
output proportional to field strength. I was struck by the
delicacy of the sensor head, looking at what must have been a very
labor intensive assembly.*
*BTW, the signal conditioning amplifier was enclosed in a ¾”
diameter by 4” long section of tubular steel, so it was obvious
that this conductive mass (not to mention the shielded,
multi-conductor power & signal cable) would distort the measured
field and degrade the isotropicity.*
**
*/Ed Price
/**WB6WSN**/
/**Chula Vista, CA USA**//*
**
*From:*Patrick [mailto:[email protected]
<mailto:[email protected]>]
*Sent:* Tuesday, March 06, 2018 7:37 AM
*To:* Edward Price
*Subject:* Re: [PSES] Field probe calibration
Hello Ed -
Good morning!
You are correct - the factors stored in the probe correct for
the non-linearities of the diode detector.
( as a side note- hearing a presentation live, and
asking/answering questions, is always more educational than a
sterile slide deck.
i wish we all could sit through this presentation, ask
questions, and have dialog. )
Did you notice the warnings about errors possible in the
calibration process?
For instance, the "probe on a stick" is calibrated at an angle???
And for that probe they say the electronics box should be kept out
of the field???
I understand the reasons, but keeping the box out of the field
is nearly impossible for most of our semi-anechoic chamber
applications!!
And I rarely see them used at the same angle as calibrated.
How does one quantify those effects?
(...a topic for another thread ?)
But, getting back to the frequency response question...
Here is what I recall-
... As shown in the slides, the detector is connected across a
small (tiny?) dipole.
the size of the dipole has some real-world limits.
large enough to capture enough power to make a measurement
possible.
small enough to minimize disturbance in the field.
the three orthogonal dipoles have to be close enough to
represent the same physical space.
So the size, placement and response is a compromise away from
"ideal" (i.e. not flat ).
... IMHO, there is nothing revolutionary in that information.
But, maybe I missed something?
Let me know your thoughts.
I would encourage local chapters to contact ETS, and ask them if
they could present at the local chapter meeting.
(DISCLAIMER - I have no affiliation with ETS, I just like the idea
of learning something new about something that was thought to be
settled...)
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