Keysight 8478B, Руководство по эксплуатации и обслуживанию

Страница: 43 / 49

Keysight 8478B Operating and Service Manual
-43
Keysight 8478B
Thermistor Mount
Operation and Service Manual
A Manual Changes
To adapt this manual to your instrument, refer to Table A-1 and make all of the
manual changes listed opposite your instrument serial number. Perform these
changes in the sequence listed.
If your instrument serial number is not listed on page 2 of this manual or in
Table A-1 below, it may be documented in a yellow MANUAL CHANGES
supplement.
CHANGE A
1. Change “Operating Resistance:” on page 15 to “200 ohms Balanced”.
2. Replace the section title “Operation with 431A/B/C or 430 Power Meters”
on page 19 to “Unbalanced Operation with 431A/B or 430 Power Meters"
and its first paragraph with following:
If the 8478B is used with a Model 431 Power Meter, a Model 11527 A
Adapter is required. If the 8478B is used with a 430 Power Meter, a Model
11528A Adapter is required. The use of an adapter breaks the balanced
circuit and an unbalanced circuit results. In this unbalanced condition, a
large amount of IO kHz audio bias signal may be coupled from the power
meter to the RF source output.
3. Delete first sentence of “Because the mount is unbalanced, a large amount
of 10kHz audio bias signal may be coupled from the power meter to the RF
source output. The RF source 10kHz output impedance forms a parallel
circuit shunt across one of the detection thermistor elements. If the RF
source presents a 10kHz impedance of 15k ohms or greater, the audio bias
voltage appearing at the RF input connection is typically 1.3 Vrms. For an
RF source 10kHz impedance of 50 ohms, the audio bias voltage is greatly
reduced to typically 5 mVrms: The presence of a large 10 kHz audio bias
Table A-1 Manual Changes by Serial Number
Serial Number or Prefix Make Manual Changes
Below 1833A C,B,A
1833A C,B
2030A C