doc: add an appendix on frequency calibration to the all-in-one manual

diff --git a/doc/Makefile.am b/doc/Makefile.am
index d7d92f2cbf76841647ffccda29882b128b4fd77d..5ca6137991c54e9cbd7fc2b3d4988bd807e88185 100644 (file)
--- a/doc/Makefile.am
+++ b/doc/Makefile.am
@@ -155,6 +155,7 @@ INC_FILES=\
        installation.inc \
        using-am-products.inc \
        updating-firmware.inc \
+       frequency-cal.inc \
        altosui.inc \
        altosdroid.inc \
        system-operation.inc \

diff --git a/doc/altusmetrum.txt b/doc/altusmetrum.txt
index 4b7699c5cd95f6fb8df6407655b59bcb0b3a97d3..41e79a2b6886840e62430162ad31701f4278f460 100644 (file)
--- a/doc/altusmetrum.txt
+++ b/doc/altusmetrum.txt
@@ -63,6 +63,8 @@ Keith Packard <keithp@keithp.com>; Bdale Garbee <bdale@gag.com>; Bob Finch; Anth
 
        include::updating-firmware.adoc[]
 
+       include::frequency-cal.adoc[]
+
        include::flight-data-recording.adoc[]
 
        include::specs.adoc[]

diff --git a/doc/frequency-cal.inc b/doc/frequency-cal.inc
new file mode 100644 (file)
index 0000000..7c66305
--- /dev/null
+++ b/doc/frequency-cal.inc
@@ -0,0 +1,71 @@
+[appendix]
+== Frequency Calibration
+
+All products that have radio interfaces require calibration of the radio
+frequency.  Normally, this calibration is done once during the production
+process and the resulting cal value is saved into non-volatile memory.  The
+procedure decribed here should only be used outside of the factory if you 
+are really convinced the radio calibration is bad, and you have access to
+the required tools to do the calibration.
+
+Because this procedure is only rarely needed in the field, we have not 
+written any fancy user interface for doing it .. some interaction with 
+and careful typing in a command-like style interface are required!
+
+=== Background Information
+
+The radio system on each board uses a quartz crystal to control
+a frequency synthesizer that can be programmed to a range of operating
+frequencies.  While these crystals are very stable, they have an accuracy
+specification that means once the base frequency they set is multiplied up
+to the typical operating range of our products, any variation also gets
+multiplied.  The objective of the calibration process is, indirectly, to
+measure the actual operating frequency of the crystal and adjust the way
+the frequency synthesizer is programmed to account for this variation.
+
+The frequency may shift a few tens of Hz over the full operating temperature
+range, and it may also shift a bit over time as the crystal ages.  But once
+properly calibrated, none of those changes are likely to ever cause any 
+operational problem, as the shift in operating frequency due to these factors
+is tiny compared to the bandwidth of our transmitted signal.
+
+=== Required Equipment
+
+The calibration process requires the ability to precisely measure the actual
+frequency of a steady CW carrier on or about the intended operating frequency
+in the vicinity of 435 MHz.  
+
+In production, we use an HP 5385A that is locked to a 10 MHz reference that 
+is in turn locked to GPS, which provides a highly accurate calibration.  Any 
+reasonably accurate frequency counter is likely to be sufficient.
+
+You also need a computer with terminal program and USB cable to attach to
+the board in question, along with a battery and power switch suitable for
+powering the board up.
+
+=== RF Calibration Procedure
+
+Using the terminal program, connect to the board over USB.  You will find 
+that you are now interacting with a command interpreter on the board.  Using
+'?' will show the available commands.  Of interest for this process are the
+'C' command which turns on a steady transmitted carrier on the currently
+selected operating frequency, and the 'c' subcommands that allow interaction
+with the saved configuration.
+
+Use the 'c s' command to discover and note the current radio calibration 
+value, and the operating frequency the board is configured for in kHz.
+
+Set up your frequency counter with a suitable antenna near the board's 
+antenna and use the 'C' command to turn on a steady carrier.  Let the
+frequency stabilize, and note what it is to as many digits as are steady
+on your counter's display.
+
+To calculate the new calibration value, the equation is:
+
+.  (intended_frequency / measured_frequency) * current_cal_value
+
+Set the new calibration value using 'c f <value>', then use 'c w' to save
+that cal value into non-volatile memory.  You can use the 'C' command again
+to confirm the operating frequency is now within a few 10's of Hz of the
+intended operating frequency.
+