High Mac,

About a year ago I was at an EMC test house. They were experimenting
with three axis short dipoles with a detector diode in between. I
never saw such a small package for a diode, maybe it was just the chip
on top of the substrate.

The output goes via a high resistance metallic layer to the interface.
The whole interface is fed by fiber optic (data also goes via fiber
optic). It wasn't used for antenna design measurements but for EMC
high field strength measurements. Their intention was to use it up to
18 GHz. Of course sensitivity (conversion from E-field to DC output)
is very poor, but for high incident field that isn't a problem.

For indicative measurements I like today's easy to get medium barrier
microwave schottky rectifiers (like BAT15 and BAT 62). Together with a
CMOS input stage opamp one can make a nice zero bias detector with
good temperature stability and that outputs the full available EMF
from the rectifying diode. So you can calculate back the incident E-
field.

Best regards,

Wim
PA3DJS
www.tetech.nl

On 10 ene, 02:35, "J. Mc Laughlin" wrote:
Dear Jim Lux W6RMK:

I was not able to examine the probes that I saw in use at NBS in what was
probably the mid-70s.

The probes that I did see and use comprised three, orthogonal, very short
doublets with attached means for rectifying. The resulting DC was conveyed
away through a resistive, plastic transmission-line crafted to be almost
transparent to RF. These probes were used to estimate the size of strong EM
signals in the vicinity of equipment so as to be able to put better numbers
on EMC capabilities.

While one can make a reasonable estimate of field strength inside of a TEM
cell (a big piece of transmission line) from external measurements, it is
desirable to be able to estimate FS at spots inside of the cell. It is
important to note that even with care, significant uncertainties remain in
the estimates. All measurement comprise a minimum of two numbers: an
estimate of the value and an estimate of the uncertainty of that estimate.
You, and most on the group, know this, but it needs to be repeated.

Safety of life was involved with the testing then done. With the profusion
of transmitters in close proximity of safety equipment today, it is a wonder
that more lives are not lost with inappropriate actuations just within
present cars. A reminder that the need for savvy RF engineers will not
diminish, and sending that work off-shore to a low-bidder is dangerous and
probably criminally negligent. The major US car makers, to pick an
industry, expend a large, expensive effort to see that their cars are safe
using resident engineers.

Warm regards, Mac N8TT
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