Elecraft PX3 Owner's Manual - Manual (Page 19)

19
How to Set Up and Interpret the PX3 Display
There are several options to customize the layout of
your PX3 display.
D I S P switches between a
spectrum-only and spectrum-plus-waterfall display.
The height of the waterfall can be adjusted with
MENU: Waterfall . The function (FN) switch
labels appear at the bottom of the screen by default.
You can hide them to maximize the screen area by
holding
L AB E L S . The FN switches remain active
even when the labels are hidden. Another trick to
maximize viewing area is to choose a smaller type
font via
MENU: Font .
Spectrum Display
The spectrum display on a panadapter is similar to
the display on a laboratory spectrum analyzer. The
horizontal axis is frequency and signal strength is
represented by the vertical height of each signal.
The PX3’s spectrum display is similar to most in
that the signal height is proportional to the
logarithm of the amplitude, represented in decibels
(dB). Each 3 dB represents a doubling of power and
10 dB means ten times the power.
The vertical scale at the left edge of the spectrum
display may be in units of dBm or S-units, as
selected by
MENU: Lvl Mode . The dBm unit
means decibels with respect to one milliwatt. 0
dBm is one milliwatt, +10 dBm is 10 milliwatts, -10
dBm is 1/10 milliwatt and so on. An S9 signal is
normally considered to be 50 microvolts into 50
ohms, which is -73 dBm, an easy number for a ham
to remember! Assuming the standard 6 dB per S-
unit, the following table applies.
S-Units Signal Level
S9 -73 dBm 50
V
S8 -79 dBm 25
V
S7 -85 dBm 12.5
V
S6 -91 dBm 6.25
V
S5 -97 dBm
V
S4 -103 dBm 1.56
V
S3 -109 dBm 0.78
V
S2 -115 dBm 0.39
V
S1 -121 dBm 0.2
V
You would expect the S meter on the KX3 and the
signal on the PX3 display to indicate the same level,
however there are several reasons why that might
not be the case. One is that the PX3 is not affected
by the preamplifier and attenuator in the KX3 when
the signal amplitude is shown in dBm.
The noise level will generally be lower on the PX3
display compared to the KX3’s S meter. The reason
is that the effective bandwidth of the PX3 is
generally one display pixel, which is approximately
the span divided by 450. The smaller the
bandwidth, the less noise. For example, if the span
is 45 kHz, the effective PX3 bandwidth is 45,000 /
450 = 100 Hz. If the KX3 bandwidth is 400 Hz, it
will show a 6 dB (one S-unit) higher noise level
than the PX3.
A similar thing happens with spread-out signals like
SSB. Even at the maximum 200 kHz span, the
PX3’s effective bandwidth is only about 440 Hz so
that not all the SSB signal is within one pixel.
That’s why the PX3 tends to read a lower level on
SSB signals than the KX3’s S meter.
R E F (reference level) on the PX3 shifts all the
signals up or down. The level that you are adjusting
is the signal level at the bottom of the display,
measured in dBm.
S C AL E is used to expand or contract the vertical
scale. Think of it as a vertical gain control. The
scale is defined as the dB difference between the
top and the bottom of the display. For example, if
the reference level is -100 dBm and the scale is 20
dB, then a signal at the top of the display is at -80
dBm. For both
R E F and S C AL E , turning the knob
clockwise makes the signals taller.
The PX3 automatically compensates for the
preamplifier and attenuator in the KX3 when the
display amplitude is shown in dBm. When you turn
them on or off, the signal levels on the PX3 should
stay the same. The indicated dBm level should be
the signal level at the KX3’s antenna input. Perhaps
counter-intuitively, this means that if you turn on
the preamplifier in the KX3, the noise level
displayed on the PX3 may decrease, rather than
increase. That is because the PX3 automatically
reduces its gain when the KX3 preamplifier is
turned on, in order to keep the signal levels the