HP 8970B, Service Manual, Page: 28 / 40

5-4 HP 8970B Option 020 Service Manual Supplement
Fault-Finding Tips
YIG Tuned Oscillator (0955-0630)
The 3 GHz LPF is board etched and there should be no reason why this would fail.
If there is low signal in the through path with Special Function 63.0 then it is either the
coupling capacitors or the 2 dB pad is damaged.
The supply and control connections are shown in Figure 1-1.
YIG Tuned Oscillator (0955-0630)
The YTO has a range of 4 to 7 GHz but we use it over the range 3.910 to 5.947 GHz.
Check pins 1,2,7,8 and 9 for correct supply voltages.
Disconnect the YTO cable from J3 on the input assembly and connect this to a spectrum
analyzer.
Set the HP 8970B to:
1. Start Frequency 10 MHz.
2. Stop Frequency 2047 MHz
3. Step Frequency 20 MHz
Set the Spectrum Analyzer to:
1. Start Frequency 3.9 GHz
2. Stop Frequency 6 GHz
3. Reference Level 20 dBm
4. Scale 2 dB/division
Ensure that the signal level measured on the spectrum analyzer is between 14 and 18.5
dBm.
Note
You can monitor the YTO from J4, which is the unused side of the splitter.
However, if you use this alternative, be aware that the levels will be
approximately 3 dB lower than when monitoring at J3.
Mixer (0955-0635)
The labelling on the schematic in figure 1 may be a little confusing but that is due to the
configuration that the mixer is being used in.
The input signal (10 MHz to 2047 MHz) is mixed up to a frequency of 3900 MHz (Lower
Sideband) by and L.O varying between 3910 MHz and 5947 MHz.
The LO port is connected to the YTO 3910 MHz to 5947 MHz
The IF port is connected to the RF input 10 MHz to 2047 MHz
The RF port is a fixed frequency output at 3900 MHz
In order for the mixer to work correctly the input level to the L.O port should be greater
than 10 dBm. This can be tested over the frequency range by carrying out the test in
section 5.3 but measured at J5 rather than the YTO output.