R.V.R. Elettronica VJ2000, User Manual

Page: 38 / 110

VJ2000
32 / 44 USER MANUAL Rev. 4.0 - 26/02/01
10) With output power at 2000 W, make small adjustments, as above, to minimize grid and
anode currents; if necessary, reduce exciter power to maintain 2000 W of output power.
8.2 Calibration of the Protection Board
Before calibrating the protection board, or IG and IA currents, remove the front panel
which also supports the RF chamber.
Disconnect the antenna output cable, remove the coaxial cable from the input connector,
undo the 8 screws holding the panel and remove the panel; take care not to disturb the high
voltage cables and the multipolar service cable.
Lay the chamber carefully on a raised surface, opposite the unit to facilitate the following
procedure.
The protection board has three trimmers for adjusting the following alarm thresholds:
insufficient fan pressure, excess V.S.W.R. and excess grid current.
These alarm conditions are indicated by three leds (Alarms Fig.1).
Remove the metal cover of the protection box by undoing the 4 screws.
The alarm thresholds may be calibrated through the following procedure:
1)
CALIBRATION OF FAN PRESSURE ALARM THRESHOLD (PRESS.).
a) Switch the ST.BY. switch (19 Fig.1) to ST.BY.
b) Enable power to the unit by switching the POWER switch (18 Fig.1) to ON.
c) Ensure that the PRESS. indicator (15 Fig.1), initially on, turns off when the air-flow
switch (3 Photo 2), positioned inside the flue, switches up (air pressure normal).
Two error conditions can prevent the above sequence from being completed: the indicator
remains on, or remains permanently off.
In this case adjust the trimmer, R4, until the sequence is completed correctly: switch
down, led on; switch up, led off.
2) CALIBRATION OF V.S.W.R.
To adjust the threshold of the V.S.W.R. alarm first perform SETUP 1.
The threshold should be set at around 10 % of the maximum output power i.e. between
170 and 200W.
a) Connect a mismatched, dummy load (e.g. 2.0KW/50 Ohm in parallel) to the RF output
of the amplifier, in series with a bypass wattmeter.
b) With the unit switched on (N.B. the rear cover must be in place) and having calibrated
the unit to its exciter frequency, gradually increase the output power from 0W until a
reflected power of 170/200W is registered on the external wattmeter.
c) Adjust the trimmer R7 until the alarm threshold is reached and the V.S.W.R. led lights
up (13 Fig.1).
N.B. Several attempts may be necessary. At least 60 seconds should be allowed
inbetween attempts to allow an automatic reset.