Page 2-6
CL40 Antenna Technical Instruction Manual
Issue 3.0
Section 2 Preparation for Use and Installation
2.5 ADJUSTING THE SPARK GAP
Adjust the antenna’s spark gap (see
Figure 2-7) as follows:
(a) Perform the necessary turn-on and
adjustment procedures for the
transmitter and ATU – as described
in their respective Technical
Instruction manuals – to achieve the
desired operating power level.
(b) Record the antenna current on the
ATU control/monitor PWB’s meter.
(c) Turn the transmitter off.
(d) Determine the antenna reactance
(X
C
) using Table 2-2.
Table 2-2:
Antenna Reactance vs Freq.
(based on 220 pF antenna capacity)
Freq.
(kHz)
X
C
(
Ω
)
Freq.
(kHz)
X
C
(
Ω
)
200 3618 375 1930
225 3216 400 1809
250 2894 425 1703
275 2631 450 1608
300 2412 475 1523
325 2226 500 1447
350 2067 535 1352
(e) Calculate the peak output voltage
(V
PK
) using either:
•
DGPS:
V
PK
= 1.414 I
A
X
L
•
NDB: V
PK
= 1.414 I
A
X
L
(1+Mod %/100)
I
A
is the current recorded from step (b)
X
L
is the reactance from step (d).
WARNING
Turn the transmitter off when making
adjustments on the antenna. Lethal
voltages are present when any level of
RF is applied to the antenna.
(f) Enter the graph below with the peak
antenna voltage calculated in step (e)
and determine the spark gap length.
If you purchased the Top Loading Kit,
multiply the peak voltage (V
PK
) result
by 0.6.
(g) Lower the antenna. Set the spark gap
for the length determined in step (f).
(h) Raise the antenna, turn on the
transmitter at the desired power level
and ensure no spark gap arcing.
2.6 ANTENNA MAINTENANCE
Nautel recommends you perform a
thorough visual inspection of the antenna
at least once every six months.
•
Check bolts and electrical connections.
•
Check the base for cracks and heaving.
•
Check the anchor post for excessive
movement within the base.
•
Check the mast’s verticality and the
mast and radiator for any distortion or
unusual vibration. If necessary, take the
appropriate remedial measures.
•
If the antenna is located near salt water
or in an area of high air pollution,
undesirable deposits may build up on
the insulator which, in turn, may impair
its performance. If the insulator
becomes visibly fouled, turn off the RF
input signal to the antenna and wash
these items with clean, fresh water.
•
Give the winch a generous coating of
grease. Alternatively, if frequent raising
and lowering of the antenna is not
expected, dismount the winch and store
it inside.
100
60
40
20
10
6
4
2
.01 .02 .04 .1 .2 .4 1
Peak An
ten
n
a V
o
lta
g
e
Gap Length
