Vector-LP Radio Beacon Transmitter Technical Instruction Manual
Page
4-5
Section 4 Testing and Adjustment
Issue 1.1
4.3.5.5 SETTING CHANGEOVER MODE
AND RF MONITOR THRESHOLDS
If a standby side is being used, adjust the
transmitter’s high and low RF power limits,
low modulation and tone levels, and the
monitor delay period, as follows:
NOTE
International Civil Aviation Organization
(ICAO) standards dictate the transmitter be
turned off or a warning alarm be generated
when the RF output decreases by at least
3.0 dB or increases by at least 2.0 dB from
the intended carrier level. The user can
alter the monitor settings provided these
criteria are still met.
(a) Disable changeover. Set changeover
control to bypass mode (see 3.6.4).
(b) Set the transmitter to the desired RF
output level.
(c) Set the transmitter for desired
modulation depth in ‘beacon’ (PTT
inactive) and ‘beacon and voice’ (PTT
active) modes (see 3.6.7).
NOTE
If the NDB is to be used only in ‘beacon’ or
‘beacon and voice’ mode, you only need to
set up the NDB for the appropriate mode.
(d) Calculate the desired low modulation
depth for each mode. Set the
transmitter to modulate at these levels.
(e) In the Monitor Timeout screen (see
3.6.7), set the monitor timeout period
(in seconds) and decide whether
shutdown will be enabled or disabled.
(f) In the Power Thresholds screen (see
3.6.7), set the high and low power
limits and press
Compute New
Thresholds
.
(g) In the Mod % Thresholds screen (see
3.6.7), press
Compute New
Thresholds
in ‘beacon’ (PTT inactive)
and ‘beacon and voice’ (PTT active)
modes (see 3.6.7). The thresholds
should be updated with the desired
values.
NOTE
At this point the system has automatically
determined to use either a current or
voltage sample to control the modulation
detection and protection circuitry.
(h) Set the transmitter for desired
modulation depth in ‘beacon’ (PTT
inactive) and ‘beacon and voice’ (PTT
active) modes (see 3.6.7).
(i) Enable changeover. Set changeover
control to normal mode (see 3.6.4).
NOTE
Changeover is inhibited when a VSWR of
1.4:1 or greater is present.
(j) Check each threshold to ensure that it
functions properly by adjusting the
transmitter beyond the desired limit
and observing that the transmitter
reacts as expected. For detailed
testing information see 4.3.5.6.
NOTE
If you manually decrease the modulation
depth, the transmitter will inhibit output
power when the tone level is below the
desired threshold. The Keying Gate
Monitor Fail A or B fault will be displayed.
To restore power, increase the modulation
level and reset the fault status.
(k) When complete, restore the transmitter
to the desired power level and press
reset to clear all alarms (see 3.6.3).
Normal operation should resume.
4.3.5.6 VERIFYING EXCITER
CHANGEOVER THRESHOLDS
Verify the exciter changeover thresholds as
follows:
(a) Set the exciter control mode to
NORMAL
(see 3.6.4). Set Keyer
Modulation to
ON
(see 3.6.13.1)
