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prod/doc/: completed description of signal strength measurement

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- test.hmac: added more details on physical test setup
- setup.hmac: described SPECTRUM_MARGIN parameter
- setup.hmac: described process for generating the reference spectrum
This commit is contained in:
Werner Almesberger 2011-05-28 13:19:45 -03:00
parent 680086b2fa
commit 33f84b436c
2 changed files with 37 additions and 1 deletions
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32
prod/doc/setup.hmac
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@ -164,6 +164,11 @@ if the host name or IP address under which the Ben is reached differs from
"ben", the value of <B>ATBEN_DUT</B> and <B>ATUSB_REF</B> will have be
changed accordingly.
<P>
The Makefile also contains the variable <B>SPECTRUM_MARGIN</B> that
defines how many dB of tolerance should be allowed below and above the
reference signal strength. The default is to allow a margin of 5 dB in
either direction.
<P>
The scripts <SAMP>atusb</SAMP> and <SAMP>atusb-flash</SAMP> also contain
configuration variables. If the names of the files containing the
<B>atusb</B> firmware binaries are not <SAMP>boot.hex</SAMP> and
@ -369,7 +374,32 @@ Ben, and if a stable temperature is maintained.
<SUBSECTION title="Signal strength">
@@@
The signal strength of a DUT is assesses by comparing it with
measurements previously obtained in the same setup, with a known to
be good device taking the role of the DUT. It is therefore necessary
to establish a reference profile each time the test environment changes,
e.g., when changing location or when using a different reference device.
<P>
The physical arrangement of the devices should have the characteristics
described in <A href="test.html#atben">the test section</A>. The orientation
of the devices should be chosen such that the overall signal strength is
near its maximum, that the spectrum is relatively "flat", and that small
changes in the orientation only produce small variations in the measured
signal strength.
<P>
To generate the profiles for <B>atben</B> and <B>atusb</B>, simply run
<PRE>
make spectrum
</PRE>
Then place the devices appropriately and press <B>D</B> in the measurement
window to use the displayed spectrum as the reference. Multiple spectra
can be merged into the reference, e.g., if environmental conditions cause
significant variations. Spectra included in the reference are shown in blue.
<P>
After a obtaining the reference spectrum, press <B>Q</B> to exit. The
Makefile will then record the signal strength limits for an <B>atben</B>
DUT in the file <SAMP>ben.profile</SAMP> and proceed with the reverse
measurement, i.e., with <B>atusb</B> acting as the DUT.
<END author="Werner Almesberger" date="<GEN_DATE>">

6
prod/doc/test.hmac
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@ -29,6 +29,12 @@ the PC, insert the <B>atben</B> board into the Ben, and place both devices
at the same location and with the same orientation used when acquiring the
signal strength profile.
<P>
The two devices should be about 1 m apart, with as few metal or watery
objects between or near them as possible. Location and orientation should
be easily reproducible, e.g., by marking the device's edges on the table
with tape. Other transmitters in the 2.4 GHz band will interfere with
measurements and should be kept as far away and as inactive as possible.
<P>
<IMG src="setup-A.png">
<P>