Sensors - microHAM SMORF Manual

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14 – SENSORS
SMΩRF connects to RF signal by remote sensor. Sensor is a box, inserted in the transmission line (coaxial
cable) from the source of power (transceiver of power amplifier) to the load (antenna) and provides attenuated
sample of current (I) and voltage (U) on load, or attenuated sample of forward (FWD) and reflected (REF) power.
SMΩRF supports both types of samples coming from sensors.
All supported HF sensors are U/I type with current and voltage transformers inside. They have no characteristic
impedance because current transformer is designed to cause minimal series impedance to load and voltage
transformer maximal parallel impedance to load. Therefore reference impedance is taken from the characteristic
impedance of the connected antenna feed line.
All VHF/UHF sensors are FWD/REF type. They are designed as directional couplers, having main line made as
a stripline, sensing line as a microstrip and have a certain characteristic impedance (50Ω, optionally 75Ω).
All sensors have internal micro-controller and EEPROM memory for calibration data storage and temperature
measurements. Each sensor is individually calibrated at multiple frequencies for each band, multiple power
levels for each frequency, and for different operating temperatures at a plane of LOAD connector, to the plane of
SMA sample connectors. These data are stored in this EEPROM memory.
When sensor is attached to the SMΩRF and is powered up for the first time, SMΩRF reads out all calibration
data from the sensor's memory and makes a copy of these data in its internal memory in order to avoid long
waiting time on every subsequent power up cycle, when SMΩRF only checks presence of the sensor. During run
time, SMΩRF takes only temperature measurements from the sensor for real time data correction.
Sensor communicates to the SMΩRF over Sensor Cables, therefore it is not allowed to insert any device in
between the sensor and the SMΩRF other than plain coaxial cable.
Please note, all U/I sensors (HF+6m) have voltage transformer connected in parallel to the LOAD connector.
For DC or low frequency AC power, transformer winding acts as a short path to ground. If you have any
controller connected to the antenna feedline, which controls some RF Box by injecting DC or AC power to the
antenna feedline (Ameritron RCS-4, some other antenna switch, preamplifier or antenna tuner working on this
principle) always connect it after the sensor's LOAD connector, towards antenna, assuming that the radio port of
such controller is DC/ low frequency AC isolated. If you are not sure, contact your vendor for details.
For parameters, frequency and power ratings of each individual sensor models please refer to the Technical
Specifications chapter.
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