This article demonstrates an automated Return Loss scan of an antenna using:
- IC-7410 transceiver with CIV;
- 40dB power attenuator;
- Return Loss Bridge (RLB);
- rfpm1 with USB data logger (A prototype data logger for RFPM1); and
- a PC orchestrating the test.
- measurement of a large number of data points;
- improved accuracy by reducing the risk of recording errors; and
- reducing the tedium of a measurement task.
The objective is to emulate what is achieved with a Spectrum Analyser with Tracking Generator, or Sweep Generator with logging power meter.
Above is a Return Loss scan of the antenna using a Spectrum Analyser with Tracking Generator and RLB. Essentially, this is the measurement to replicate with the simpler ham shack equipment.
Above is a block diagram of the test configuration.
The PC controls the IC-7410 using the built in USB CIV port. The RF output of the IC-7410 is attenuated to a level safe for the RLB. The the antenna system is connected to the DUT port of the RLB, and the other port connected to the RFPM1 power meter. The RFPM1's USB data logger is connected back to the PC to allow automated recording of the power level.
The test is controlled by a script on the PC.
@echo off rem :more rem RIGCTL parameters set MODEL=367 set PORT=COM15 set SPEED=4800 rem scan loop parameters set freq=7000000 set inc=10000 set steps=21 set RIGCTL="C:\Program Files\hamlib-w32-3.0\bin\rigctl" set RIGCTLP=%RIGCTL% -m %MODEL% -r %PORT% -s %SPEED% del capture.txt rem main scan loop for /L %%i in (0,1,%steps%) do call :measf %%i %RIGCTLP% set_ptt 0" goto l1 rem subroutine to make each measurement :measf %RIGCTLP% set_mode RTTY 300 set_freq %freq% set_ptt 1 rem sleep 1 rem measure set meas= set /p meas="Measure %freq%: " rem set /a result=%RANDOM% echo %freq% %meas% echo %freq% %meas% >>capture.txt set /a freq=%freq%+%inc% exit /b echo falling through :l1 set meas= set /p meas="Stop HID input then ENTER to quit:" echo meas :%meas% if not *%meas%==* goto l1 :end
Above is an example Windows bat file to orchestrate the measurement. The script sends configuration commands to the transmitter, and waits for the measurement result and writes it to a log file.
#!/bin/bash #RIGCTL parameters MODEL=367 PORT=/dev/ttyUSB0 SPEED=4800 #scan loop parameters freq=7000000 inc=10000 steps=21 RIGCTL="/usr/bin/rigctl" RIGCTLP="$RIGCTL -m $MODEL -r $PORT -s $SPEED" #echo RIG: $RIGCTLP >capture.txt trap "break;" SIGINT for ((i=$steps;i;i--)); do $RIGCTLP set_mode RTTY 300 set_freq $freq set_ptt 1 read -p "Measure $freq: " obs if [ -z "$obs" ]; then break fi #timestamp=`date +"%Y%m%d%H%M%S"` #echo -e "$timestamp\t$obs" echo -e "$freq\t$obs" echo -e "$freq\t$obs" >>capture.txt freq=$(($freq+$inc)) done #loop until the HID input is turned off while true; do read -p "Stop HID input then ENTER to quit:" obs if [ -z "$obs" ]; then break fi done trap - SIGINT $RIGCTLP set_ptt 0
Above is an example *nix Bash script to orchestrate the measurement. The script sends configuration commands to the transmitter, and waits for the measurement result and writes it to a log file.
The measurement involves three phases:
- an ‘open' calibration scan with nothing attached to the RLB DUT port (0dB RL);
- a ‘measurement' scan with the DUT attached; and
- calculation and reporting of the difference between 1 and 2, RL, and from that, VSWR.
Above is a plot of the calculated Return Loss and VSWR.
There are a couple of bumps in the graph which could be reduced by averaging several readings (say 10) in the script file, an exercise for the reader.
An automated Return Loss sweep using a CIV controlled transmitter, suitable power attenuator, and the RFPM1 with data logger is quite feasible.
References / Links