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1、Service Manual H 6960 Vol. 2 RF Power Meter 6960 Including Option 3964-650 (GPIB Interface) AMENDMENT RECORD The following amendments are incorporated in this manual. Amendment Date No. Mar. 85 July 86 Am. 1 Am. 2 3 Apr. 87 Nov. 87Am. 4 Issued at serial no.: 518 1069 1570 1820 MARCONI INSTRUMENTS LT
2、D. 1984 Printed in the UK Print code: D-11 /87, MI 3c Nov. 87 (Am. 4) Part no, 46881-553L Page (i) RadioFans.CN 收音机爱 好者资料库 H 6960 Vol. 2 CONTENTS PRELIMINARI ES Title page Contents Notes and Cautions CHAPTERS I General inforniation 2 Ins tallation These chapters contained in a 3-1 3-2 Operation Appl
3、ications separate Operat1ng Manual Vol. I. 4 Technical description 5 Maintenance 6 Replaceable parts 7 Servicing diagrams HAZARD WARNING SYMBOLS The following symbols appear on the equipment Type of hazard Reference in Static sensitive device Vol. 2, Page (iv) Supply voltage Vol. 2, Page (iii) Note
4、. Each page bears the date of the original issue or the code number and date of the latest amendment (Am. I, Am. 2 etc.). New or amended material of technical importance introduced by the latest amendment is indicated by triangles positioned thus f to show the extent of the change. When a chapter is
5、 reissued the triangles do not appear. Any changes subsequent to the latest amendment state of the manual are included on inserted sheets coded Cl, C2 etc. Page (ii) June 84 RadioFans.CN 收音机爱 好者资料库 H 6960 Vol. 2 NOTES AND CAUTIONS ELECTRICAL SAFETY PRECAUTIONS This equipment is protected in accordan
6、ce with IEC Safety Class 1. It has been designed and tested according to IEC Publication 348, Safety Requirements for Electronic Measuring Apparatus, and has been supplied in a safe condition. The following precautions must be observed by the user to ensure safe operation and to retain the equipment
7、 in a safe condition. Defects and abnormal stresses Whenever it is likely that protection has been impaired, for example as a result of damage caused by severe conditions of transport or storage, the equipment shall be made inoperative and be secured against any unintended operation. of covers Remov
8、al of the covers is likely to expose live parts although reasonable precautions have been taken in the design of the equipment to shield such parts. The equipment shall be disconnected from the supply before carrying out any adjustment, replacement or maintenance and repair during which the equipmen
9、t shall be opened. If any adjustment, maintenance or repair under voltage is inevitable it shall only be carried out by a skilled person who is aware of the hazard involved. Note that capacitors inside the equipment may still be charged when the equipment has been disconnected from the supply. Befor
10、e carrying out any work inside the equipment, capacitors connected to high voltage points should be discharged; to discharge mains filter capacitors, if fitted, short to gether the L (live) and N (neutral) pins of the mains plug. Mains plug The mains plug shall only be inserted in a socket outlet pr
11、ovided with a protective earth contact. The protective action shall not be negated by the use of an extension lead without protective conductor. Any interruption of the protective conductor inside or outside the equipment is likely to make the equipment dangerous. Primary fuses Note that there is a
12、supply fuse in both the live and neutral wires of the supply lead. If only one of these fuses should rupture, certain parts of the equipment could remain at supply potential. To provide protection against breakdown of the supply lead, its con nectors, and filter where fitted, an external supply fuse
13、 (e.g. fitted in the connecting plug) should be used in the live lead. The fuse should have a continuous rating not exceeding 6 A. June 84 Page (Hi) RadioFans.CN 收音机爱 好者资料库 H 6960 Vol. 2 sure that only fuses with the required rated current and of the specified type are used for replacement. The use
14、of mended fuses and the short-circuiting of fuse holders shall be avoided. CAUTION: STATIC SENSITIVE COMPONENTS Components identified with the symbol on the circuit diagrams and/or parts lists are static sensitive devices. The presence of such devices is also indicated in the equipment by orange dis
15、cs, flags or labels bearing the same symbol. Certain handling precautions must be observed to prevent these components being permanently damaged by static charges or fast surges. (I) If a printed board containing static sensitive components (as indi cated by a warning disc or flag) is removed, it mu
16、st be temporarily stored in a conductive plastic bag. (2) If a static sensitive component is to be removed or replaced the following anti-static equipment must be used. A work bench with an earthed conductive surface. Metallic tools earthed either permanently or by repeated discharges. A low-voltage
17、 earthed soldering iron. An earthed wrist strap and a conductive earthed seat cover for the operator, whose outer clothing must not be of man-made fibre. (3) As a general precaution, avoid touching the leads of a static sen sitive component. When handling a new one, leave it in its con ducting mount
18、 until it is required for use. (4) If using a freezer aerosol in fault finding, take care not to spray programmable ICs as this may affect their contents. WARNING: HANDLING HAZARDS This equipment is formed from metal pressings and although every endeavour has been made to remove sharp points and edg
19、es, care should be taken, particularly when servicing the equipment, to avoid minor cuts. Lithium: A lithium battery is used in this equipment. Under no circum stances must any lithium battery be crushed, incinerated or disposed of in normal waste. They must be separately and securely packed and any
20、 exposed electrical connections adequately insulated to avoid a short circuit occurring during transit. They must be clearly identified to show the nature of the hazard and then disposed of in a safe manner by an authorized toxic waste contractor. WARNING : TOX I C HAZARD Many of the electronic comp
21、onents used in this equipment employ resins and other chemicals which give off toxic fumes on incineration. Appropriate precautions should therefore be taken in the disposal of these items. Page (iv) Mar. 85 (Am. 1) H 6960 Vol. 2 Chapter 4 TECHNICAL DESCRIPTION CONTENTS Para. IOverall circuit descri
22、ption 6 Detailed technical description 6 Analogue p.c.b. 47 Power reference 51 Processor p.c.b. 70 Keyboard and display p.c.b. 72 GPIB interface module 80 Software description Table Page 1 Attenuator control . 4 2 Sensor Zener voltages6 3 PPI port allocations 16 Fig. 1 RF Power Meter 6960 block diag
23、ram 2 2 First amplifier 3 3 Spike blanking4 4 Overall timing 7 5 7543 Serial D-A 8 6Step-up voltage regulator 9 7 8 9 10 11 12 Step-down voltage regulator . Machine cycle : Wait state and Fetch Memory decoding Simplified reset control Interface bus structure Handshake procedure . instruction (AAOZ)
24、10 12 14 15 18 20 OVERALL CIRCUIT DESCRIPTION 1. a Refer to the 6960 block diagram shown low d.c. voltage when power is applied. in Fig. 1. This d.c. The r.f. sensor gi signal is converted ves to an a.c. signal by the signal chopper enabling high gain, low noise amplifiers to be used. 2. The chopped
25、 signal is fed to the first amplifier which is split into two parts, the first part being in the r.f. sensor package and the other in the power meter. The signal is then passed to the spike blanking circuit which removes spikes on the edges of the square wave signal produced by the signal chopper. T
26、he following buffer also corrects for sensor non-linearities. The signal is then fed to the 1st attenuator which, together witb the 2nd attenuator controls the gain of the amplifier strip in 10 dB steps. The 2nd and 3rd amplifiers provide the rest of the required gain. The 4th amplifier, together wi
27、th the gain D-A, provides fine adjustment of the a.c. gain. Chap. 4 June 84 Page 1 H 6960 Vol. 2 3. The phase synchronous detector then synchronously de-modulates the a.c. signal. Timing signals for the signal chopper, spike blanking and the detector are provided by the timing logic. The recovered d
28、.c. signal passes to the peaking meter and, via a switch to the comparator. 4. The microprocessor runs the program stored in read only memory. Data storage is achieved by using non volatile RAM (Random Access Memory) Outputs from the microprocessor drive the zero D-A, the 14 bit D-A, the gain D-A, t
29、he recorder D-A, the attenuator drives, the liquid crystal display, the GPIB interface and the power reference. Inputs to the microprocessor are taken from the comparator, the keyboard and the GPIB interface. 5. Power for all of the stages is provided by the PSU. DETAILED TECHNICAL DESCRIPTION Analo
30、gue p.c.b. 6. Refer to Chap. 7, AAOI circuit diagram. 7. First amplifier (sheet I). ICI and associated components form the second part of the 1st amplifier, the first part being in the power sensor assembly. When using the 6910 series sensors this amplifier has a gain of approximately 1000. Fig. 2 s
31、hows a simplified complete amplifier. 8. AC gain is controlled by the components in the emitter circuit of the power sensor transistor. DC bias for the transistor is set by RI to RS. C2, C6 and C9 control the high frequency response and the capacitor in the sensor controls the low frequency response
32、. The amplifier has a band-pass characteristic centred at the chop rate of 925 Hz. Chopped signal output Fig. 2 Chap. 4 June 84 Page 3 .-J H 6960 Vol. 2 9. 0 VA control. Ie2, RIO, RII and TRI provide a very low offset source follower which provides an earth reference from the signal ground in the po
33、wer sensor. This earth reference, indicated by 0 VA, is used by the rest of the a.c. gain stages. DI, D2 and R9 ensure that the earth reference only moves a small amount (about 0.5 V) when no sensor is connected to the power meter. ID. Spike blanking. The spike blanking circuitry, R114, Cl6 and IC3c
34、, remove spikes that are generated on the leading and trailing edges of the chopped d.c. signal from the r.f. sensor (see Fig. 3). IC3c and CI6 act as a sample and hold circuit. The hold period is from the signal chopper changes state and lasts for a period of 180 RI14 reduces errors caused by the h
35、old time interfering with large signal levels at high r.f. power levels. IC4b acts as a high impedance buffer for the signal from the sample and hold. SAMPLE/HOLD J TIM ING I I CHOPPED D. C. OUTPUT CCS084 Fig. Spike 11. First attenuator. Precision resistors RI4 and Rl5 with IC3a, IC3b form a switcha
36、ble, divide by 100 attenuator for range changing (see Table 1). C23 together with the resistors forms a high-pass filter for bandwidth control. TABLE 1 ATTENUATOR CONTROL es Range attenuation IC10a IC10b I None ON OFF ON OFF OFF 2 1/ 10 ON OFF OFF ON OFF 3 1/100 OFF ON ON OFF OFF 4 1/1000 OFF ON OFF
37、 ON OFF 5 1/10000 OFF ON OFF OFF ON Chap. 4 June 84 Page 4 H 6960 Vol. 2 12. Second amplifier. IC4a with feedback components R22 and R23 form the second amplifier. The gain is approximately 25. C35 controls the high frequency roll off. 13. Second attenuator. R24 to R26 and ICI0 form the second atten
38、uator. The principle of operation is the same as the first attenuator described above. This attenuator also has a divide by 10 setting. 14. Third amplifier. The third amplifier stage has a gain of about 35. Resistors R30 and R31 control the gain of IClla. C38 controls the high frequency roll off. 15
39、. Fourth amplifier. The fourth amplifier is different from the other amplifier stages, in that its gain can be controlled very precisely. It is basically a standard gain stage (ICllb, R3?, R38), but having both inverting and non-inverting inputs. The main signal is applied to the non-inverting input
40、 which has a gain of approximately 3. When a signal is applied to R37 and the inverting input, from the gain D-A which uses the signal as its reference, the gain of the amplifier is reduced. This the gain to be finally controlled over the range I to 3. 16. Phase synchronous detector (sheet 2). The i
41、nput a.c. signal is restored to d.c. by this circuit. Samples of the signal are taken on each half cycle by closing the switches ICI4a and IC14d alternately, with c49 and C50 charg ing up to the sample voltage during the time the switch is closed. These sample and hold capacitors must be able to cha
42、rge and discharge rapidly to ensure a fast response to changes in signal level. The time constant is determined by the effective impedance of the switch and the qutput of 4th amplifier ICllb and the value of C49 and C50. Together theSe allow an almost complete sample to be obtained within the sample
43、 period. i 17. When the power meter is on the most sensitive range (range 1), resistors R53 and placed in series with the coupling switches. These in crease the charge time of the capacitors so forming a very frequency low pass filter. 18. ICI5 acts as an instrumentation amplifier offering a high im
44、pedance to C49 and CSO so maintaining their charge and allowing a shift of earth refe rence to the 0 VC reference used throughout the d.c. stages. Precision resistors R34, 35, 36 and 42 ensure that the gain on each input is the same otherwise linearity errors would result if these differed. 19. The
45、output from ICISb is then fed to the peaking meter via R78 and the comparator, ICI?, via switch ICI6b. This output is also used for the level ling output after being passed through the low-pass filters, R58 and C60, and buffer ICI8b. Chap. 4 June 84 Page 5 . H 6960 Vol. 2 20. Comparator and A-n conv
46、ersion. The comparator output is taken to the Serial Input Data (SID) pin of the processor. The inverting input is driven from the 14-bit D-A. The non-inverting input is driven from either the phase-synchronous detector or the Zener diode in the sensor. This arrange ment allows the processor to make
47、 successive approximation analogue-to-digital conversions. To do this the processor sets the most significant bit of the 14-bit D-A. It then reads SID to check the output of the comparator. If the output of the comparator is high the data is kept; if not the bit is set to reset. The processor contin
48、ues by setting each bit in turn, deciding whether to keep or discard each bit until all 14 bits have been checked. 21. Sensor Zener diode drive. The Zener diode in the sensor is used to decide which type of sensor is in use. The Zener diode is driven ftom a 5 mA constant current circuit consisting o
49、f R77, RII6, DID, DII and TRI4. The voltage from the Zener diode is scaled by RI12 and RI13 before being applied to the comparator. 22. The type of sensor in use defines the required scaling and linearity corrections that must be applied to give a true power reading. Table 2 indicates the Zener voltages used with the appropriate scaling and corrections that are applied. TABLE 2 SENSOR ZENER VOLTAGES Zener Sen
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