MISCELLANEOUS, Continued:

NUMBER OF DATA POINTS (N):

This is also the number of samples that will be processed by the FFT if that mode is active, but note that although the raw output of the FFT will contain this many points, it takes two output values to make one frequency line in the spectrum display, which shows the resultant magnitude of both the Cosine (Real) and Sine (Imaginary) outputs of the FFT. So there will only be half as many spectral lines in the (unexpanded) display as shown by N.

In general, if you double the number of lines in a spectrum by doubling N, any random noise will be spread over twice as many spectral lines. Each line will thus have half the noise power (3 dB lower). Note that this is exactly the result obtained by waveform averaging twice as many sweeps at the smaller N, such that the total number of samples considered is the same.

PAUSE:

In addition to this explicit manual operation, Daqarta will also enter Pause mode at the completion of an average. The Pause option will also be highlighted, but the status will be shown as Done.

When Daqarta is in Pause mode, all data collection is halted unless you are recording in DDisk mode. In that case, the DDisk recording continues and only the trace is frozen. You may want to do this to better examine some detail of the trace, without disrupting the actual recording. If you want to stop the recording, use the spacebar DDisk Skip or the Remote Control, if activated.

Whenever MemSv or MemRd is used to save to or read from trace memory, Pause is also activated. MemSv just results in the normal Pause status display, but MemRd shows the status as 'Mem n' where n is the memory trace number.

Similarly, if a file is loaded from disk, the status will show 'FILE'.

Pause mode is also entered automatically after a Single Sweep (Singl) operation.

Note that during Key Macro operation, the grey Pause/Break key (but not the P-key) instead functions as a macro Halt or Step key, as does NUM-LOCK.

PLUG-IN MODULES:

Daqarta allows these modules to access internal variables and functions, and to replace functions with those provided by the module. Modules may access functions and data in other modules, enabling standard libraries to be built and shared. Note, however, that a library module should usually be loaded before modules that will use it, so that it will be found when those modules are initialized at load time. Load order is determined simply by order of appearance in DQA.CFG.

Due to the complexity of interfacing plug-in modules with main Daqarta modes and functions, this is best left to experienced developers. All code is in assembly language, and great attention to detail is required. A plug-in developer's kit is being planned to make this easier, with source code for typical working modules and a Help compiler for use with the CTRL-Help system. Serious developers should contact Interstellar Research for more information.

Interstellar Research requests no royalties from developers who sell plug-in modules, as long as they make it clear to their customers that the sale does not include Daqarta itself, which is shareware.

QUIT Daqarta:

    'Save changed Key Macros?  (Y default/N):'

Note that there is no prompt to save changed palettes to a file.

REMOTE CONTROL SWITCH CONTRUCTION:

Shielded coaxial cable is the best choice if the remote cable must pass into an electrically shielded room.

The switch setup must be able to provide an acceptable TTL level to the I/O port on the acquisition board. Many boards provide +5 Volts at their connectors, but if yours does not you will have to find it somewhere. Many serial ports provide +5 Volts... check yours with a voltmeter. If all else fails, you can always find +5 Volts inside the case of any regular (non-portable) computer at the disk drive connectors, etc, so you might be able to tap into that if you feel competent.

TTL devices require that zero be a short circuit, not an open circuit, so you should wire your switch like this:

                               .---- +5 Volts
                               |
                               |
                               R = 1K to 10K
                               |
             Cable center      |
   .---------------------------^---- Digital Input
   |
  \  Switch
   |
   `-------------------------------- Digital Ground
             Cable Shield

When the switch is open, the digital input receives +5 Volts through the resistor, whose value is not critical. When the switch is closed, the digital input is shorted to ground and a small current flows through the resistor and switch.

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