HP 8970b schematic

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HP 8970B Option 020

Service Manual Supplement

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Service Manual Supplement

HP 8970B Option 020

HP Part no. 08970-90115

Edition 1 May 1998

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UNIX is a registered trademark of AT&T in the USA and other countries.OSF/Motif is a

trademark of the Open Software Foundation, Inc. in the USA and other countries. © Copyright Hewlett-Packard Company May 1998 All rights reserved. Reproduction, adaptation, or translation without prior written

permission is prohibited, except as allowed under the copyright laws. Printed in the UK.

ii HP 8970B Option 020 Service Manual Supplement

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Printing History

Date

May 1998 1 08970-90115

Manual Edition

Notes

HP 8970B Option 020 Service Manual Supplement iii

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List of Related Publications

HP Part Number Title

08970-90054 HP 8970B Noise Figure Meter Service Manual

About this Manual

This document is a supplement to the HP 8970B Noise Figure Meter Service Manual (08970-90054) and provides information useful for operating the HP 8970B Option 020. It also gives some troubleshooting tips.

iv HP 8970B Option 020 Service Manual Supplement

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Table of Contents

Page

Printing History.....................................................................................................iii

List of Related Publications .................................................................................. iv

About this Manual................................................................................................. iv

Block Diagram and Parts List.................................................................................... 1-1

Block Diagram......................................................................................................... 1-2

Front End ................................................................................................................1-3

Material List ........................................................................................................... 1-5

Theory of Operation..................................................................................................... 2-1

General.................................................................................................................... 2-2

Adjustments.................................................................................................................... 3-1

General.................................................................................................................... 3-2

Input power detector Gain and Offset Adjustment............................................... 3-2

600 MHz SAW Oscillator Frequency Adjustment................................................. 3-3

Board Differences .........................................................................................................4-1

General.................................................................................................................... 4-2

Microprocessor Board ............................................................................................. 4-2

20 MHz IF Assembly (08970-60050)......................................................................4-3

Driver Assembly (08970-60089)............................................................................. 4-4

Fault-Finding Tips........................................................................................................5-1

General.................................................................................................................... 5-2

Filter (0955-0634) ................................................................................................... 5-2

Input Assembly (08970-60097 or 08970-60125)....................................................5-3

YIG Tuned Oscillator (0955-0630)......................................................................... 5-4

Mixer (0955-0635)................................................................................................... 5-4

Isolator (0960-0638)................................................................................................ 5-5

4.5 GHz Low Pass Filter (9135-0169).................................................................... 5-5

Second Convertor (5086-7909) ............................................................................... 5-6

600 MHz SAW Oscillator (08970-60093)............................................................... 5-6

Board Details.................................................................................................................. 6-1

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Contents-2 HP 8970B Option 020 Service Manual Supplement

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Block Diagram and Parts List

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Block Diagram and Parts List

Block Diagram

Figure 1-1: HP 8970B Option 020 Front End Schematic

2.05 GHz Low Pass Filter

PAD 1

PAD 2

PAD 3

4.5 GHz LPF

O/P

(924) (925)

(926)

ISOLATOR

+15 V (2)

20 dB AMP (923)

DETECTOR (927)

INPUT ASSEMBLY

I/P

-15 V (7)

50 Ω

MIXER

TO A4 ASSEMBLY

4 - 6 GHz Y.T.O

J4 J3

Second Convertor

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LO MONITOR

600 MHz SAW Oscillator

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Front End

Block Diagram and Parts List

Front End

Figure 1-2: HP 8970B Front End Schematic

2050 MHz LPF

10 - 2047 MHz

Limiter

10 dB

20 dB

INPUT ASSEMBLY

Limiter (on 08970-60125 Input Assembly only). Suppresses externally generated transients.

10 dB

2-7 GHz Isolator

10 dB

Detector Diode

Output

4.5 GHz LPF

2 dB

YTO Output

3.910 - 5.947 GHz

600 MHz

3.9 GHz

300 MHz

To A4 Assy

3.6 GHz

X 6

2nd Convertor

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Block Diagram and Parts List

Front End

Figure 1-3: Schematic Representation of Input Assembly

PAD 1 20 dB

Limiter

10 dB PAD

Limiter (on 08970-60125 Input Assembly only).

This is a schematic representation of the RF input assembly. The ampliﬁer section and each and each of the attenuator sections are switchable by the control lines.

On units using the Input Assembly 08970-60125, the Limiter suppresses externally generated transients.

In Figure 1-1 the numbers in brackets inside the input assembly refer to the wire colors. The numbers at the side of the second convertor refer to the wire colors attached to the

connector which connects up to the second convertor.

20 dB AMP

Amp

PAD 2 PAD 3

10 dB PAD

Detector

3 GHz LPF

2dB PAD

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Block Diagram and Parts List

Material List

Table 1-1: HP 8970B Option 020 Material List - main differences for Option 020

Description Part Number Quantity

2.05 GHz Low Pass Filter 0955-0634 1 Semi-rigid cable W1 08970-20082 1 Input Assembly 08970-60097 1 Input Assembly 08970-60125 2 to 8 GHz YIG Tuned Oscillator 0955-0630 1 YIG Tuned Oscillator Interface Board 08970-60045 1 YIG Tuned Oscillator Shield 08590-00047 1 Semi-rigid cable W2 08970-20081 1

Semi-rigid cable W3 08970-20083 1 Semi-rigid cable W4 08970-20085 1 Microwave Mixer 0955-0635 1 Semi-rigid cable W5 08970-20084 1 Microwave Isolator 0960-0638 1 Right Angle SMA(F) to SMA (M) Adapter W6 1250-1249 1

4.5 GHz Low Pass Filter 9135-0169 1 SMA(M) to SMA (M) Adapter W7 1250-2189 1 Second Convertor 5086-7909 1 600 MHz SAW Oscillator 08970-60093 1 Flexi Cable W8 83711-60035 1 Flexi Cable W9 83711-60035 1 Main Wiring Harness 08970-60046 Firmware EPROM’s 08970-80071/72 20 MHz IF Assembly 08970-60050 Driver Board Assembly 08970-60089

1 2 1 1

SMA (M) 50 Ω Termination 0960-0053 1

1. Replaces 08970-60097 from preﬁx break 3811.

2. This is the same part number as the main instrument but different wires are used. The wires that are not used are tied back.

3. These replace 08970-80051/52

4. Replaces 08970-60003

5. Replaces 08970-60034

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Block Diagram and Parts List

Material List

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Theory of Operation

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Theory of Operation

General

The input range of the instrument is 10 MHz to 2047 MHz. The input signal is ﬁrst low pass ﬁltered, using the 2050 MHz ﬁlter, to avoid images. The YIG tuned oscillator tunes over the range 3910 MHz to 5947 MHz to mix the

incoming signal to a ﬁrst IF of 3900 MHz. The isolator ensures that any rejected signals are absorbed in the isolator and do not

interfere with the front end detector circuitry. The second convertor mixes 3900 MHz down to 300 MHz. There is a cavity tuned

bandpass ﬁlter which is tuned for 3900 MHz. This is set at the factory and should not be adjusted. The LO input is 600 MHz, but this is multiplied up to 3600 MHz by a X6 circuit. The 3600 MHz can be monitored at the LO Monitor port.

The 600 MHz supplied to the second convertor comes from a 600 MHz SAW Oscillator.

The frequency is adjusted for 600 MHz ± 50 KHz. The power should be > -3 dBm.

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Adjustments

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Adjustments

General

There are 2 adjustments that need to be made:

1. Input power detector gain and offset.

2. The 600 MHz SAW oscillator frequency adjustment.

Input power detector Gain and Offset Adjustment

Follow the adjustment procedure in section 5-13 of the Adjustments Chapter in the 8970B Service Manual with the following exceptions.

Figure 3-1: Input detector gain and offset adjustment

RF Input Assembly

R26

1. The input level must be -21 dBm ± 0.1 dB.

2. R32 is the offset adjustment.

3. R26 is the gain adjustment.

R32

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Adjustments

600 MHz SAW Oscillator Frequency Adjustment

Figure 3-2: 600 MHz SAW Oscillator Frequency Adjustment

8568A

RF In

600 MHZ SAW Oscillator

1. Disconnect the 600 MHz SAW Resonator from the second convertor 600 MHz input.

2. On the 8568A. Press PRESET, CENTRE FREQUENCY 600 MHz, SPAN 500 KHz.

3. Connect the 600 MHz SAW Resonator to the 8568A RF Input.

4. Adjust R6 until the signal on the screen is 600 MHz ± 50 KHz.

HP 8970B Option 020 Service Manual Supplement 3-3

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Adjustments

600 MHz SAW Oscillator Frequency Adjustment

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Board Differences

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Board Differences

General

As well as the complete front end being changed there are a number of board differences that need to be documented here.

Microprocessor Board

The same part number 08970-60033 is used in both instruments. However the ﬁrmware is different for the option 20 compared to the standard.

Table 4-1: Firmware Part Numbers

Options ROM #1 ROM #2

STD 08970-80050 08970-80051

Option 20 08970-80070 08970-80071

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Board Differences

20 MHz IF Assembly (08970-60050)

The 08970-60050 assembly has been created from the 08970-60003 assembly with the following changes.

1. C83 changes from 7.5 pF (0160-3029) to 4.7 pF (0160-3873)

2. R8 changes from 110 Ω (0757-0402) to 162 Ω (0757-0405)

Figure 4-1: Schematic differences in 08970-60050

+15V (F1)

C23

0.01 uF

L11

22 uH

162 Ω+15V (F1)

1000 Ω

C22

0.01 uF

C83

4.7 pF

C21

1 uF

1000 Ω

7.3 TO

7.7 Vdc

1780 Ω

14.6 TO

15.3 Vdc

R10

51.1 Ω

Q20

20 MHz BANDPASS FILTE

C26

56 pF

L12

1.5 uH

C 20

6.5 TO

6.9 Vdc

C24

0.01 uF

-15V (F1)

1.Differences are highlighted with a shaded background.

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Board Differences

Driver Assembly (08970-60089)

The 08970-60089 assembly has been created from the 08970-60034 assembly with the following changes:

1. R25, 26, 27, R39, R40 and R41 change from 214.2 Ω (0699-1911) to 121 Ω (0699-

3460)

2. Q2 is deleted and a wire is place between U33 pin 14 and the base of Q3.

Figure 4-2: Schematic differences in 08970-60089

R25

R57

R26

121 Ω

R27

121 Ω

(SEE NOTE 9)

R39

121 Ω

U33D

R24

3060 Ω

C28 1 uF

121 Ω

100 Ω

V (F1)

C58

6.8 uF

-5 VOLT

REGULATOR

VR2

13V

R40

121 Ω

1ST LO DRIVE

R41

121 Ω

C55

1000 pF

1ST LO GND

1.Differences are highlighted with a shaded background.

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Fault-Finding Tips

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Fault-Finding Tips

General

The Option 20 front end is relatively easy to fault ﬁnd because it is a combination of deﬁned RF components.

Instead of using the noise source it is possible to use a signal generator to inject a signal and then trace the signal levels through the RF paths to the 300 MHz second IF using a spectrum analyzer. It is much easier to do it this way because the signals can be seen on the spectrum analyzer display.

Filter (0955-0634)

The speciﬁcations on this part are:

Table 5-1: 2050 MHz Low Pass Filter Speciﬁcations

Frequency Insertion Loss

10 MHz to 2050 MHz < 0.5 dB

2.35 GHz to 3.85GHz > 35 dB

3.85 GHz to 13.0 GHz > 65 dB

13.0 GHz to 26.5 GHz > 50 dB

The best way to measure this part is to use a network analyzer. An alternate way is to use a spectrum analyzer, e.g. 8593E with a tracking generator or a separate sweeper.

Verify over the frequency ranges above that the insertion losses are correct.

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Input Assembly (08970-60097 or 08970-60125)

Figure 5-1: Input Assembly

Fault-Finding Tips

PAD 1 20 dB

Limiter

10 dB PAD

Limiter (on 08970-60125 Input Assembly only).

The easiest way to determine any problems with this section is to use a signal generator or sweeper which can cover the frequency range 10 MHz to 2047 MHz and can output -20 dBm.

The main source of problem with this assembly is that the pads are not switching or the ampliﬁer has been blown up. The common error when this is the case is error 27. The philosophy of repair for this assembly is board level repair so these diagnostics are intended to prove that the assembly is defective or not and replace it.

20 dB AMP

Amp

PAD 2 PAD 3

10 dB PAD

Detector

3 GHz LPF

2dB PAD

From the functionality viewpoint it is possible to check that pads and ampliﬁer are working individually by using Special 63.X.

To verify the pads and ampliﬁers of with the 8970B completely boxed up use the procedure “RF Attenuator Checks” in the Service Sheet BD1 section of the standard 8970B manual. The voltages will be approximately correct.

It is also possible to measure the pads switching with the input section removed. Using a 30 MHz signal at -20 dBm measure at J2 using a spectrum analyzer.

1. Select Special 63.0 and take a reference on the Spectrum Analyzer (straight through).

2. Select Special 63.1. The level should go down by ~10 dB from 1 (PAD 1).

3. Select Special 63.2. The level should increase by ~20 dB from 1 (AMP).

4. Select Special 63.4. The level should decrease by ~10 dB from 1 (PAD 2).

5. Select Special 63.5. The level should decrease by ~10 dB from 1 (PAD 3).

If it is necessary to look for power holes in any of the components then sweep the input and monitor the output over the desired frequency range.

The detector can be checked by going through the detector check as indicated in “Input power detector Gain and Offset Adjustment”, on page 3-2.

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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.

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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

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Fault-Finding Tips

Second Convertor (5086-7909)

This part contains a X6 multiplier, a bandpass ﬁlter, a mixer and a lowpass ﬁlter. The 3900 MHz is mixed with the 600 MHz (multiplied by 6) to give a 300 MHz IF.

Internally the 3900 MHz is bandpass ﬁltered and the 300 MHz is lowpass ﬁlter to prevent the generation of images.

Under no circumstances should the bandpass ﬁlter be adjusted as this is a very complicated process and will impair the performance of the microcircuit.

1. J1 is the RF input at 3900 MHz.

2. J2 is the IF output at 300 MHz

3. J3 is not used

4. J4 is the LO input at 600 MHz. Power should be between -1 and +4 dBm.

5. J5 is the LO monitor at 3600 MHz. This is about -30 dBm with the above input range for the 600 MHz.

The conversion loss between the 3900 MHz input at J1 and the 300 MHz output at J2 is about 6 dB. With a -25 dBm input signal at J1 the output at J2 would be approximately

-31 dBm. It is possible to verify these levels by using a signal generator and a spectrum analyzer. The supply connections are shown in Figure 1-1.

600 MHz SAW Oscillator (08970-60093)

This board delivers the 600 MHz to the second convertor. Figure 3-2 shows the adjustment procedure.

The frequency should be 600 MHz ± 50 KHz

The power should be > -3 dBm

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