16 • BX-240
© Box 73 Amateurfunkservice GmbH 2017
Display Lighting
The possibilities are
On
,
Off
, and
Auto
.
With the automatic option the lighting will
turn off after a time, turning on again after
some user action (button press). It is rec-
ommended to use the device without light-
ing or, at least, in automatic mode as the
current consumption for a graphic display
is quite high (Fig. 28).
Correction of the frequency
generator
All the internal frequency values are de-
rived from a 27 MHz Quartz crystal. A
variation of about a hundred Hertz is not
uncommon and can be compensated for
using software. To do so a frequency of
27.000000 MHz should be set in the
Fre-
quency Generator
mode. A calibrated fre-
quency counter should be connected to the
analyzer output socket and the difference
between the measured and adjusted fre-
quency determined. After selecting the
menu item
Delta Frequency
press the left
button. The value for
d
f
is then adjusted
using the middle and right buttons to the
determined difference (27.000000 MHz
less measured frequency). Press the
D/S
button again to select the decimal place.
Repeated pressing of this button will dis-
play the abbreviation
ENT
. If the plus or
minus button is pressed now, the FA-VA4
will take the set value as the frequency
correction amount. Now the frequency of
the analyzer output signal should corre-
spond exactly to the set value. Naturally,
in the course of this, changes in tempera-
ture may lead to deviations of the quartz
frequency, a frequency correction here is
at the limits of quartz oscillator stability.
In the case of antenna measurements,
however, a deviation of a few hundred
Hertz or even a kiloHertz is usually non -
critical, so the described correction may
only be necessary in rare cases (Fig. 29).
Fig. 28: Settings for display lighting
Fig. 29: Input possibilities for the frequency
correction factor
