Digital Monitoring XR6 Manual do Utilizador descarregar pdf (Página 8)

Page 6 of 7 XR3/XR6 Frequency Change Procedure

Issue 1.0 IS07012

(c) While monitoring the RF current and

voltage, ensure that the RF current

lags the RF voltage by at least 40 ns

(see Figure 7).

t = 40 ns

Figure 7: Current Lagging Voltage

(d) Increase the PA voltage to 70 V. The

RF current should be 6 A ± 2 A. Verify

that the RF current lags the RF voltage

by at least 40 ns.

(e) Increase the PA voltage to 130 V for an

XR6 or to 90 V for an XR3. The RF

current should be 11 A ± 1 A for an

XR6 or 7.75 ± 1 A for an XR3. Verify

that the RF current lags the RF voltage

by at least 40 ns.

2.4.3 MINIMIZE HARMONIC CONTENT

WARNING

To avoid personal injury, the

transmitter must be in an RF Off state

with ac power switched off during

adjustments made in this section.

(a) Install the RF current probe (Delta

probe) in the transmitter’s RF output

feed line. Terminate the current probe

with a suitable dummy load and

spectrum analyzer. NOTE: Each side

of the RF filter cover must be tightly

secured with at least one screw while

the transmitter is in operation.

(b) Apply ac power to the transmitter and

press RF On. Increase the RF output

to 6 kW for an XR6 or to 3 kW for an

XR3 and monitor the second and third

harmonic levels on the spectrum

analyzer.

(c) Carefully adjust the SYMMETRY

potentiometer (R32) on the active

exciter’s RF synthesizer PWB to

minimize the second harmonic. Switch

to the other exciter and adjust the

SYMMETRY potentiometer (R32) on

that exciter’s RF synthesizer PWB to

minimize the second harmonic.

(d) Set the spectrum analyzer’s marker

on the third harmonic peak and note

the level. If the level is more than 80

dB below the carrier, no adjustment is

required. If not, press RF Off and

switch off the ac power to the

transmitter.

(e) Gain access to the RF output filter and

make a small adjustment to inductor

L4 (see Figure 3) by moving the L4

coil clamp to add or subtracting a few

inches of coil.

(f) Install the cover on the output filter,

apply ac power, and press RF On.

Check the level of the third harmonic

compared to the level noted in step

(d). If the level increased the coil

clamp was moved in the wrong

direction. If the level decreased the

coil clamp was moved in the correct

direction. Continue adjusting until the

third harmonic can no longer be

reduced.

(actual waveforms may contain ringing)

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