                          Linrad calibration.

The analog hardware may use filters with poor frequency response.
It is a good idea to design analog filters for optimum dynamic range,
which means steep skirts but not very flat passband. The calibration
procedure adds a digital filter with a frequency response that is
the inverse of of your hardware's response. As a result the digital
data sent into Linrad for further processing is filtered through
a filter with perfectly flat amplitude response and perfectly linear
phase response.

The calibration procedure has to add one more filter, the desired
frequency response, because frequencies that are absent can not be 
recovered. The desired frequency response must be chosen for the
total digital filter to not have extreme gain or Q.

Each mode has to be calibrated separately. There may be perfectly
valid reasons to use different shapes for the desired frequency
response in different modes. Calibration is slow however and you
do not actually have to run the calibration procedure for all the modes.

You may calibrate in one mode and then copy the file to produce
the calibration files for all other modes that you want to share the
same calibration. The calibration files are:

   Mode                    Frequency response
Weak signal CW             dsp_wcw_corr
Normal CW                  dsp_cw_corr
Meteorscatter CW           dsp_hsms_corr
SSB                        dsp_ssb_corr
FM                         dsp_fm_corr
AM                         dsp_am_corr
QRSS CW                    dsp_qrss_corr
TX TEST                    dsp_txtest_corr       
SOUNDCARD TEST MODE        dsp_test_corr
ANALOG HARDWARE TUNE       dsp_tune_corr

If your hardware is set up to run in direct conversion mode with
two audio channels for each HF channel, you also have to calibrate
for the amplitude and phase balance errors of your hardware.
In direct conversion mode you need these files also:

   Mode                    Channel balancing data
Weak signal CW             dsp_wcw_iqcorr
Normal CW                  dsp_cw_iqcorr
Meteorscatter CW           dsp_hsms_iqcorr
SSB                        dsp_ssb_iqcorr
FM                         dsp_fm_iqcorr
AM                         dsp_am_iqcorr
QRSS CW                    dsp_qrss_iqcorr
TX TEST                    dsp_txtest_iqcorr       
SOUNDCARD TEST MODE        dsp_test_iqcorr
ANALOG HARDWARE TUNE       dsp_tune_iqcorr

TX TEST is always one channel so it needs its own calibration
files if your system is set up for two channels. Otherwise
you may copy these files from a single calibration file.

Rather than making multiple files you can use symbolic links.
Note that a calibration change in one mode then will change
the calibration in all modes.
