Varian UNITY INOVA NMR, Hardware Installation, Page: 48 / 65

6.2 Testing RF Transmitter Performance
01-999044-00 C0501 UNITY INOVA Solids Hardware Installation
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If this is not the value, adjust the potentiometer R83 (in zone P4) on the board to
obtain it. (The range is from 80 mA (4.96 V) to 160 mA (9.92 V)).
7. Reassemble the amplifier and return it to the cabinet.
6.2 Testing RF Transmitter Performance
This series of tests evaluates the third cabinet relay and attenuator operation as well as
the 1 kW amplifier power output and performance.
Figure 20 illustrates the third
cabinet status panel.
1. The blanking signal from the connector J7023 should show correct levels. During
REC ON the level is low and during REC OFF the blanking signal is high. If this not
the case, you can change each output to the correct level by moving the blanking
polarity select jumper J1 on the Solids Relay Driver board. Confirm that the blanking
gate cable is connected to the amplifiers.
2. Using a 30-dB, 500-W attenuator, check the input at J7710 as described in step 7
below. Add at least a 20-dB attenuator in series if you are using a spectrum analyzer.
3. Make sure that the power to the third cabinet and the low-voltage power supply are
on. Wait 3 minutes.
4. After three minutes , switch on the EHT supply and make sure of the following:
•
The EHT voltage readout is 2.2 kV or greater.
•
The EHT current is no more than 2.2 mA (pulsed mode) or 55 mA (CW mode).
5. Carefully tune the cavity amplifier. See “Tuning the High-Power (Cavity) Amplifier”
on page 44 for the tuning procedures.
6. Perform the following amplifier tests:
a. With both LO BAND and HI BAND set to LO POWER , enter
rtp('/
vnmr/stdpar/H1')
to recall parameters.
d. Set the following parameters: nt=1e6 sw=1e5 np=128 pw=2e3
d1=0.1 gain=0 tpwr=63 .
e. Enter
go
. Check that no rf is present at the input of the amplifier.
f. Enter aa and wait for the abort message. Set the HI BAND switch to HI
POWER. Verify rf power of at least 44 dBm.
g. Stop the acquisition. Move the spectrum analyzer input with the 500-W
attenuator to transmitter cable at the preamplifier. Set the HI BAND
switch to
LO POWER.
HI BAND
CW
PULSE
TEMP
DUTYCYC
P WIDTH
OVER DR
LO BAND
CW
PULSE
TEMP
DUDTCYC
P WIDTH
OVER DR
OFF ON
SHUT OFF CAUTION
LO
POWER
HI
POWER
HI
POWER
PLATE
CURRENT
GRID
CURERENT
- + - +
LO
POWER
HI BAND
LOBAND
STATUS
HI POWER ENABLE
AC
POWER
Figure 20. High-Power Amplifier Control Panel on the Solids Cabinet