HP 8970B, Руководство по обслуживанию, Страница: 29 / 40

HP 8970B Option 020 Service Manual Supplement 5-5
Fault-Finding Tips
Isolator (0960-0638)
Note
J5 should be the same level as J4 (the other side of the splitter). Therefore you can
make both YTO and Mixer measurements from J4.
The conversion loss is < 7dB. This is the loss between the IF port and the RF port with the
LO > 10 dBm.
The best way to do this is at spot frequencies say 100 MHz steps or if the problem is at a
known frequency then do it there. The example is for 100 MHz.
Setup the 8970B. Preset, Frequency 100 MHz, Special 63.0
Set the source for -20 dBm, 100 MHz
Measure the signal level at J2 and record it.
Connect the mixer in place and measure the signal at the RF port. This will be at 3900
MHz.
The difference between the 2 signal levels should be less than 7 dB.
Isolator (0960-0638)
This device will improve the match looking back from the 4 GHz low pass filter.
The insertion loss will be between 1 dB and 1.2 dB depending on the temperature.
This can be measured with a network analyzer, a spectrum analyzer and tracking
generator or a spectrum analyzer and sweeper.
The operating frequency of the isolator is 2 to 7 GH but we need only check it 50 MHz
either side of 3900 MHz.
4.5 GHz Low Pass Filter (9135-0169)
The specifications on this part are shown in Table 5-2.
These specifications can be verified by using a network analyzer, a spectrum analyzer
with a tracking generator or a spectrum analyzer with a sweeper.
Table 5-2: 4500 MHz Filter Specifications
Frequency Insertion Loss
DC to 4050 MHz < 0.5 dB
DC to 4500 MHz < 1 dB
6300 to 8400 MHz >60 dB