ETS-Lindgren HI-1710 Microwave Measurement System (Archived) - Manual (Page 40)

HI n 1710 Manual Page — 35
5.0 THEORY OF OPERATION
The HI-1710 uses a unique diode/dipole antenna sensor
developed by Holaday Industries, Inc. This sensor is
coupled with digital filtering techniques also developed by
Holaday Industries, Inc. for Automatic Microwave Oven
Scanner Systems. A radial array of eight antennas is
located perpendicular to the axis of the probe handle. The
electric field is detected by hot carrier diodes operating in
the square law region. A negative voltage is applied to
the cathode connection of the diodes to bias them in an
optimum operating region. The bias is adjusted
individually for each probe/preamp assembly. The diode
signals are summed and input to two stages of
amplification. The amplifying stages perform analog
filtering to minimize external interference at 60 Hz.
The analog output of the preamplifier is connected to one
input of a seven channel analog to digital converter. The
bias input is connected to another channel. Scaled values
of the various power supply voltages are connected to
the remaining inputs. The digital equivalent of the RF
signal is input to the 64180 microprocessor. A software
implemented filter is used to condition the RF signal for
most effective RF measurement. The filtering in the
HI-1710 is accomplished by a cascaded, iterative
software filter which simulates a Butterworth low pass
filter. Sets of fixed filter parameters can be selected from
the front panel of the HI-1710.
Selecting Filter 1 (F1) results in a digital filter
characteristic of a two pole Butterworth filter with a
cutoff frequency of 0.5 Hz. This response is equivalent to
the "SLOW" response of the common analog microwave
survey meter.
Archived 4/2/10