Measuring the Sband transmitter power
The transmitter "Antenna forward Power" is
measured via a directional coupler in the output
waveguide. The continental system provides measurement hardware. We
have also installed on HP power meter (called the LRO power meter
since the lro experiment donated it) that take its signal off of the
2nd port of the coupler.
- the rf signal is taken from a directional coupler after the
comber (see dana's schematic).
- The signal is detected and the the voltage from the
detected power is returned via the TTI_8 analog input module
(schematic 190162 XA08) word 08.
- The 732.c program processes and displays the value
- the variable meter holds the input value
- the input voltage in converted to power in the routine:
metering (in metring9.c)
- metring9 calls rfpwr3 (in math9.c)
- rfpwr3 converts voltage to watts with a lookup table
- the returned value in meter is then scaled by
scale/1.c0000. (2400/10000) to put the value in Kwatts.
- The voltage to watts lookup table was changed by phil on
- jon hagen measured a new set of values which were then
installed in rfpwr3().
- The old table is accessible in the routine rfpwr33. this
routine is only there for reference.
- The rfpwr3() lookup table is used also used for the
kly1,kly2,and waster forward power measurements.
The lro power meter.
- The lro power meter was installed around 17nov11.
- dana's schematic shows the connections. It uses the 2nd port
of the continental coupler.
- The power is read by the monLro program running on the
da crate (/home/phil/vw/datatk/mon/monLro.c)
- It reads the power meter via the gpib bus that goes up to
- The program records the power every 10 seconds. It writes to
the file /share/obs4/lro/pwrdata.log.000
- The output is ascii mjd.fract
- Sometimes there are some extra ^@@@ at the beginning of
- The dbm power has +/- in front of the number. Sometimes
this sign gets dropped. Just look at the numbers around it
to see what the sign should be.
- There is 82.8db attenuation (as of aug12). add this to get
the measured dbm.
- The users starts, stops the lro power meter from the vw%
prompt on the da crate
- the tcl procedure: monlro
- helpdt monlro to get a
- source: /home/online/Tcl/Proc/gen/monrlo.proc
- doc: /home/online/Tcl/Help/monrlo.help
Plotting the power vs detected voltage lookup table (.ps)
- I took the current and old lookup tables from the 732.c
program and plotted power vs voltage.
- The black curve is the conversion from voltage to power
table installed 11feb04.
- The green curve is the original voltage to power table that
came from continental.
- The green line shows what the lro power reading would be
given the black line.
- You can see that the old red table is a closer match to the
lro values than the current black line.
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