EVMSPEC
by Peter Martinez G3PLX
peter.martinez@btinternet.com
High Blakebank Farm
Underbarrow
Kendal
Cumbria

EVMSPEC is a spectrum analyser program for the DSP56002EVM connected to
a PC operating under DOS.

EVMSPEC takes an audio input to the left channel, and transforms it from
the time-domain to the frequency domain, displaying on the screen of the PC
a graph showing the amplitude of input signals as a function of signal
frequency. This can be a very useful tool for analysing the signals from
the audio output of SSB radio receivers, modems, tone and sound generators,
musical instruments, bells, and many others.

INSTALLATION
============
There are just two files needed to run this system: EVMSPEC.CLD and
EVMSPEC.EXE.

The first step is to load EVMSPEC.CLD into the EVM and run it. This can
be done with the EVM56K debugger program, or any other loader program,
including the G3PLX bootstrap loader described later. Once EVMSPEC.CLD is
running, connect the user port of the EVM to the COM port of your PC. Start
EVMSPEC.EXE, adding /p2 on the commandline if you are using COM2 (or /p3 or
/p4). The system should now be running. Check that you can move the
yellow diamond-shaped mouse cursor. If it will not respond, Hit F4 to
exit the program and check the EVM and/or the COM port.

If you have the G3PLX bootstrap loader in FLASH ROM, you do not need to
load EVMSPEC.CLD via the debugger, but can start EVMSPEC.EXE straight away
with /b added to the commandline. EVMSPEC.EXE then loads EVMSPEC.CLD itself
through the user COM port.

OPERATION
=========
As the program starts, the spectrum display covers the frequency range
150Hz to 3350Hz, with the centre of the horizontal axis at 1750Hz. The
vertical axis is scaled from 0dB at the top to -60dB at the bottom. The
top corresponds to an audio input of about 2.5v pk-pk (0dBm). COnnect a
suitable input to the left channel and you should see the spectrum move
upscreen.

The centre frequency can be adjusted in three ways:

 1. The left and right cursor keys move the frequency by the equivalent
    of one screen pixel up and down.

 2. You can click or drag the tuning cursor along the frequency scale at
    the bottom of the screen.

 3. You can right-click on a point in the display, for example an
    interesting spectral component, and the centre frequency will change
    to that of this point. That is, the display will be "centred up" on
    this spot.

Note that it is possible to take the centre frequency low enough that the
left-hand end of the display goes negative, or high enough that the right-
hand end goes above 4 kHz. The display does not work outside these limits,
and what you see below 0 and above 4 kHz is a mirror-image of the spectrum
inside the range.

The frequency span can be adjusted in two ways:

 1. The PgUp and PgDn keys can be used to select between scanwidths in the
    range 3200, 1600, 800, 400, 200, and 100Hz.
 2. You can click the mouse on the up- and down-arrows in the scanwidth
    box at the top of the screen.

Note that as you narrow down the scanwidth to "zoom in" on a feature of
interest in a spectrum, you will probably need to retune the centre-
frequency. You will also see that the display changes more slowly as you
change to narrower scanwidths. This is not a feature of the software, but
a fundamental physical fact: the narrower you go in bandwidth, the slower
things happen.

The gain of the display can be changed in two ways:
If the signal you are looking at is a lot less that 2.5v p-p, you can
increase the input gain by using the up-cursor key, or by clicking the
mouse on the up-arrow key in the gain box. Note that if you increase the
gain, not because the overall input is low, but because there is one
small spectral component that you want to boost, you will overload the
analyser when the overall signal excedes 2.5 v p-p. Overloading the analyser
will cause it to display spurious spectral components.

Pausing the display.
You can freeze the display by clicking on the PAUSE legend in the mode box
(top left) or by keying F3. Clicking again on PAUSE or keying F3 again will
restart the analyser.

Measuring the signal.
At any time, whether paused or not, you can click the mouse on a point in
the display, and the SPOT FREQ and SPOT LEVEL boxes will show the
frequency and level at that point.

The waterfall display.
By clicking on the WATERFALL legend in the mode selection box, or by
pressing F2, the display changes to one where the X-axis becomes time,
the Y-axis becomes frequency, and the signal level is represented by the
brightness of the display. This type of display is sometimes called a
spectrogram. It is most useful for analysing signals which change with
time, such as the outputs of modems, or even the scales and chord sequences
of musical recordings. The centre-frequency, span, and gain selections work
the same as they do in the spectrum mode, and you can also read spot
frequencies and levels, although the readings are not as accurate as they
are in the spectrum mode. The waterfall screen is a monochrome screen.

Saving to file.
You can save the spectrum or waterfall display to a file, by first typing
a file name. You can type in the filename at any time while the program
is running: you don't need to stop the display. The name that you type will
appear in the .BMP SAVE box (top right). You can backspace to change the
filename, or key ESC to cancell it. When you have entered the name
(8 letters maximum) and you are ready to save the display, key ENTER or
click in the .BMP SAVE box and the display will be saved into the current
directory and with the extension .BMP  This file is in a WINDOWS BMP format,
with 16 colours. If you wish to save to another directory, you can enter
the pathname with the /d commandline parameter. The pathname you enter must
end with a backslash.

Warnings.
This program is intended to run on a modern PC under DOS. It will probably
not run at all, or run very slowly, under WINDOWS. It may run into trouble
on an older machine which is too slow. This is because the program does a
lot of very fast graphics and fast serial communication.

Source files.
In case some users wish to edit the .CLD file, for example to change to
right channel input, or to switch in the prre-amp, the full source file
for EVMSPEC.CLD is included in the package. THIS SOURCE FILE MUST NOT BE
USED FOR COMMERCIAL PURPOSES WITHOUT PERMISSION FROM ME. If you need to
modify the .EXE file for any reason, contact me for the Pascal source file.

Have fun.

Peter Martinez G3PLX

See separate file PLXBOOT.TXT for details of the G3PLX bootstrap loader.