Spectrum Analyzer Version 1
The graph displays the signal level for the frequency range chosen. The centre
of the spectrum scan is the cursor frequency at the start of the scan. The
cursor frequency can be adjusted up and down by using the left and right arrow
keys. The frequency scan starts at the cursor frequency and sweeps up and down
to the graph edges. When the cursor frequency is changed, the centre frequency
and the centre of the scan remains unless the cursor is moved beyond the graph.
At this point, a new scan is started with the centre frequency as the cursor
frequency. The frequency step size can be adjusted from 20kHz to 10000 kHz
using the up and down arrow keys. These function like a zoom for the frequency
display. Either the vertical or horizontal spectrum can be displayed using the
red and green buttons. In the scanning mode, the OK key will replot the
spectrum with the cursor frequency as the centre. The i key uses the cursor
frequency and tries to identify the symbol rate by trying some popular symbol
rates. If a lock is found for the signal, then the symbol rate and FEC will be
displayed. The yellow key allows the checking of a custom symbol rate. The
positioner is not moved initially. The user position is taken from the database
and must be correct for acurate positioner movement using the USALS setup menu.
Controls
OK Key: This clears the spectrum window and starts a new spectrum plot with the
centre of the plot set to the cursor frequency displayed in the upper right of
the screen. The display starts at the centre frequency and moves upward and
downward in frequency plotting the high and low frequencies alternately. The
current step size is used to determine the frequencies that are plotted. The
LNB is adjusted for the frequency being sampled. To prevent un-necessary LNB
setting, the algorithm is:
if ((freq > LNB_LOW_FREQ+INPUT_HIGH_FREQ) && (LNB_freq == LNB_LOW_FREQ))
then switch the LNB to high freq
if ((freq < LNB_HIGH_FREQ+INPUT_LOW_FREQ) && (LNB_freq ==
LNB_HIGH_FREQ)) then switch the LNB to low freq
This allows the minimum of LNB switching when operating near the midpoint
Left / Right Arrow Key: These adjust the cursor frequency. The frequency range
is from 10700 MHz to 12500 MHz. If the cursor frequency is adjusted beyond the
current window of the graph, the spectrum display is restarted with the cursor
frequency at the centre of the display.
Up / Down Arrow Key: These change the step size of the spectrum display. The
step size can be adjusted from 20 KHz to 10000 KHz. The default value when the
plugin is started is 1000 KHz. Adjusting the cursor frequency by a large amount
is easier if you first change the step size to 10000 kHz, then move the cursor
frequency, and adjust the step size back to a more reasonable value like 1000
kHz.
Red Key: Clears the spectrum window and plots the Vertical spectrum using the
current step size and the cursor frequency as the centre frequency.
Green Key: Clears the spectrum window and plots the Horizontal spectrum using
the current step size and the cursor frequency as the centre frequency.
Yellow Key: Allows a symbol rate from 1000 to 50000 to be checked using the
cursor frequency.
Blue Key: Shows a help screen.
Page Up / Page Down Key: These move the positioner. At the start of the plugin,
the positioner is not changed. Single presses of the Page Up or page Down keys
increment the positioner angle by 0.1 degree, and continuous press increment or
decrement by 1.0 degree. The user location is shown on the screen and is taken
from the database. The database is updated by the USALS setting menu as in the
DGS firmware.
Volume Up / Volume Down Key: This changes the DC bias level for the spectrum
display. At the default, this gives a reasonable display on my system with
Hotbird.
i Key: This checks the cursor frequency and tries to identify the symbol rate
and FEC, by trying a number of typical symbol rates. EXIT or MENU will escape
from this checking. This checking stops the frequency display until completed
or EXIT/MENU is pressed.
EXIT/MENU Keys: If currently displaying the spectrum, this ends the plugin. If
in the Help screen or checking the symbol rate, this escapes and restarts the
spectrum display.