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------------------------------------------------------------------------ r7997 | k1jt | 2017-08-03 19:18:34 +0100 (Thu, 03 Aug 2017) | 2 lines More User Guide updates. ------------------------------------------------------------------------ r7998 | bsomervi | 2017-08-04 19:03:54 +0100 (Fri, 04 Aug 2017) | 5 lines Optimize decoded text display to limit heap usage Decoded text line now use considerably less heap memory as they accumulate. This change also limits the maximum number of decode lines saved per session to 5000. ------------------------------------------------------------------------ r7999 | k1jt | 2017-08-04 19:07:23 +0100 (Fri, 04 Aug 2017) | 1 line Text and figs for User Guide on Frequency Calibration. Still need same for Reference Spectrum and Equalization. ------------------------------------------------------------------------ r8000 | bsomervi | 2017-08-04 23:00:20 +0100 (Fri, 04 Aug 2017) | 1 line Add missing MOC generated source include ------------------------------------------------------------------------ r8001 | bsomervi | 2017-08-04 23:00:35 +0100 (Fri, 04 Aug 2017) | 1 line Remove \r and \n from process stdout so Windows looks like everthing else ------------------------------------------------------------------------ git-svn-id: svn+ssh://svn.code.sf.net/p/wsjt/wsjt/branches/wsjtx-1.8@8002 ab8295b8-cf94-4d9e-aec4-7959e3be5d79
75 lines
3.5 KiB
Plaintext
75 lines
3.5 KiB
Plaintext
=== Frequency Calibration
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Many _WSJT-X_ capabilities depend on signal-detection bandwidths no
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more than a few Hz. Frequency accuracy and stability are therefore
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unusually important. We provide tools to enable accurate frequency
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calibration of your radio, as well as precise frequency measurement of
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on-the-air signals. The calibration procedure works by automatically
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cycling your CAT-controlled radio through a series of preset
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frequencies of carrier-based signals at reliably known frequencies,
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measuring the error in dial frequency for each signal.
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You will probably find it convenient to define and use a special
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<<CONFIG-MENU,Configuration>> dedicated to frequency calibration.
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Then complete the following steps, as appropriate for your system.
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- Switch to FreqCal mode
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- In the _Working Frequencies_ box on the *Settings -> Frequencies*
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tab, delete any default frequencies for *FreqCal* mode that are not
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relevant for your location. You may want to replace some of them with
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reliably known frequencies receivable at your location.
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TIP: We find major-city AM broadcast stations generally serve well as
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frequency calibrators at the low frequency end of the spectrum. In
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North America we also use the standard time-and-frequency broadcasts
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of WWV at 2.500, 5.000, 10.000, 15.000, and 20.000 MHz, and CHU at
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3.330, 7.850, and 14.670 MHz. Similar shortwave signals are available
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in other parts of the world.
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- During the calibration procedure, the radio's USB dial frequency is
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offset 1500 Hz below each *FreqCal* entry in the default frequencies
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list. As shown in the ecreen shot below, detected signal carriers
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therefore appear at about 1500 Hz in the WSJT-X waterfall.
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image::FreqCal.png[align="left",alt="FreqCal"]
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With modern synthesized radios, small measured offsets from 1500 Hz
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will exhibit a straight-line dependence on frequency. You can
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approximate the calibration of your radio by simply dividing the
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measured frequency offset (in Hz) at the highest reliable frequency by
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the nominal frequency itself (in MHz). For example, the 20 MHz
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measurement for WWV shown above produced a measured tone offset of
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24.6 Hz, displayed in the _WSJT-X_ decoded text window. The resulting
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calibration constant is 24.6/20=1.23 parts per million. This number
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may be entered as *Slope* on the *settings -> Frequencies* tab.
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A more precise calibration can be effected by fitting the intercept
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and slope of a straight line to the whole sequence of calibration
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measurements, as shown for these measurements in the graph plotted
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below. Software tools for completing this task are included with the
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_WSJT-X_ installation, and detailed instructions for their use are
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available at https://physics.princeton.edu/pulsar/k1jt/FMT_User.pdf.
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Using these tools and no specialized hardware beyond your
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CAT-interfaced radio, you can calibrate the radio to better than 1 Hz
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and compete very effectively in the ARRL's periodic Frequency
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Measuring Tests.
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image::FreqCal_Graph.png[align="left",alt="FreqCal_Graph"]
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=== Reference Spectrum
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WSJT-X provides a tool that can be used to determine the detailed
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shape of your receiver's passband. Disconnect your antenna or tune to
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a quiet frequency with no signals. With WSJT-X running in one of the
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slow modes, select *Measure reference spectrum* from the *Tools* menu.
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Wait for about a minute and then hit the *Stop* button. A file named
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`refspec.dat` will appear in your log directory.
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[ ... TBD ... ]
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=== Equalization
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[ ... TBD ... ]
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