Operating instructions

AVIONICS SYSTEM
B-13
The test signal is an amplitude modulated RF carrier, set to the required frequency, level and
modulation depth. The selected tone sequence can be applied as a continuous reoccurring signal
or as a one shot tone burst
Setting the RF frequency
The RF frequency of the SELCAL test signal can be set to any frequency within the range of the
RF generator (400 kHz to 1050 MHz).
Pressing the [RF freq] key will highlight the 'RF Freq:' legend on the display and allow the
indicated frequency to be changed by using the variable control, or by using the data keys to enter
a new value.
Setting the RF level
To change the RF level first press the [RF Level] key, then enter the required level using the data
entry keys or use the variable control to adjust the displayed frequency. See RF frequency and
level on page B-8.
Setting the AM depth
The depth of modulation of the RF carrier is set by first pressing the [AM Depth] key and then
entering the required value using the data keys and the [%] terminator key or by adjusting the
value using the variable control.
The range of modulation depth available is 0 to 99%.
Setting the tone sequence
The tone burst is made up of two dual tone pulses as shown in Fig. B-4 tone pulse format and
timing diagram on page B-6.
To select the frequency of each tone in the burst the [Edit Sequ] soft key is pressed to display the
edit sequence menu From this menu, each tone is selected by pressing the [
⇑ ] or [ ⇓ ] key to cause
the code letter reverse video cursor to scroll through the list of frequencies and then pressing the
[Enter] key. The first letter in the first pair of letters will change to the selected letter. Repeating
the above procedure will change the second letter of the first pair. Then the first letter of the
second pair and finally the last letter of the second pair. Further repeats will cause the first letter
of the first pair to change again and so on.
Activating the tone burst
The RF signal is present at the selected RF output connector at all times when the ‘SELCAL’
function is selected.
To start a continuous sequence of tones press the [Cont Tones] key.
To start a one shot tones burst press the [Tones Burst] key.
To stop a continuous sequence of tones press the [Tones Burst] key; the sequence will stop after
one tone burst.