GRATREAD.TXT   Instructions for reading Spectrum Analyzer graticule.
                December 8, 1997   by   Scott R. Kelly 

        To read the Analyzer CRT it must be understood that the top line 
of the graticule is the REFERENCE LEVEL.  It's initial value is set by the
REFERENCE LEVEL Switch.  Values of +20, 0, -20, or -40 dBm are typical.
( For those who prefer dBmv, top line is, +69, +49, +29, or +9 dBmv.)
        
        For working in dBm numbers, use the left side for reading values.
If using numbers followed by dBmv, use the right side for reading values.
The numbers on both sides are equivalent, and are correct only when the
REFERENCE LEVEL Switch is at the 0dBm position.  Otherwise, for other REF.
LEVEL Switch positions the value must be calculated relative to the top line.

        The graticule is divided into blocks, each about a centimeter square.
The horizontal lines of these divisions are equal to 10dB each, when SCALE
Switch (VERTICAL SENSITIVITY) is at 10dB / Div.  ( the "y axis" )

        The vertical lines are the "x axis" and are Frequency relative, their
value is determined by the SPAN Switch and or the VARiable SPAN control.
The center verticle line is the CENTER FREQUENCY reference as shown on the         
LCD reading, and is also the "center of expansion" point for the VARiable
SPAN Control when the HORIZONTAL POSITION is set properly.

        The signal power reading is the horizontal line that the "peak"
of the signal envelope reaches.  The absolute value is determined when the
REF. LEVEL is known (as set by REF. switch), and the signal peak is somewhere
below.  When the REF. is 0dBm the reading can be made using the left or right
side values.  When the REF.is set otherwise, the difference must be accounted
for.  At the center line of the graticule there are four other vertical 
sub-divisions between each of the lines, these will allow finer readings 
of signal peak to within 2dB or less. VERT position is set prior to reading.

So in other words, the vertical amplitude of the signal is not the power, 
but where the "peak" of the signal comes to be (in the vertical direction),
follow that point over horizontally to one side or the other for value.
        
        It is very important that the VERTical position be set properly.
This is done by setting the REF. LEVEL to 0dBm (+49dBmv), at full VAR SPAN,
(0-500  BAND for PSA-35\37 users, and 50 MHz/DIVision for PSA-65\70\75 users)
There should be no signal cable attached, and the unit has warmed up.
Now, position the base line, or noise floor, between the tic-marks, 
near the lower corners of the graticule, at -65dBm.   VERTical position
knob is typically at a 12 O'Clock position.  DO NOT readjust VERT when
other REFERENCE LEVELS are selected!!!  To do so would give false readings.
VERT position should be checked periodically, but only in those settings
as given above.  ie, 0dBm REF, at correct SPAN and BAND, and NO input.

        The amplitude accuracy is best when the signal of interest is at 
the center of the screen, the VARiable SPAN is near zero, and SWEEP is slow.  
This way there is no loss due to deflection limits.  Sweep Rate should not
be too fast, moderate to slow is best.  Note deflection loss when Span is
full and Sweep Rate is too fast, erroneous readings >10dB are typical.

        The VERTICAL SENSITIVITY, or SCALE dB\DIV, switch is only a        
relative scale, not absolute.  When switch is in the 2dB\DIV position,
the difference between each horizontal line is 2dB.  The VERT position
can be adjusted over most of the 60dB dynamic range, for viewing signals.


EXAMPLE...
        Unit is ON and warm, 10dB/DIV, the VERT and HORIZ adjusts made, 
(baseline at -65dBm, and CF expansion point is at the center of the screen).
If a -40dBm signal is injected, while the REF. LEVEL is at 0dBm, the peak
of the signal will be four divisions down from the top line.
(This signal can also be read as +9dBmv.)  Signal should be CF TUNED, using
the correct BAND for the PSA-35\37, or the 50 MHz/DIV with the PSA-65\70\75.

With a switch of the REF.LEVEL to the -20dB position the signal peak jumps 
up two divisions.  The power hasn't changed, but the REF. LEVEL has.
The top line is now -20dBm, the next line down is -30dBm, and your signal 
is on the following line down, a power of -40dBm.

Another switch of the REF. LEVEL to -40dBm position will bring 
the signal peak to the top line of the graticule, -40dBm.
A jump of the baseline may have been noticed when the -40dBm REF.LEVEL was
selected, that is normal.  The instrument is now in its' most sensitive mode.
The baseline level may be near to a value of -90dBm or so.  Remember...
DO NOT readjust the VERT position to move the baseline back down.
Narrower band width resolutions, as available in the PSA-65's lower detent
SPANs, the baseline will move down even further because more noise is being
filtered out by the IF Board.  The other SPAN settings should still show
the peak of a -40dBm signal at the top line in the -40dBm REF.LEVEL.  
ie, The amplitudes of all the SPAN settings should match one another.(PSA-65)
        
        Proper adjustment of the HORIZontal position is accomplished by
tuning a signal (usually the Zero MHz Marker) to the center of the screen.
Then slowly turn the VAR SPAN counterclockwise(CCW), while keeping the signal
from leaving the screen with the CENTER FREQUENCY TUNING (CF TUNE).
Continue using CF TUNE and VAR SPAN until VAR SPAN is full CCW,moderate sweep,
and the maximum amplitude of the signal is CF TUNED as high, vertically,
as it will go.  Now turn the VAR SPAN full clockwise.  The CF signal
can now be moved with the HORIZontal position to the center line of the
graticule if necessary.  Older model analyzers with HORIZ knobs are typically
at the 12 O'Clock position.  Newer analyzers have a recessed control pot,
that is factory set and should not need any adjustment, but can be if needed.