Racal_RA-117_serv_user.pdf

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1、Racal RA-117 Radio Receiver 1. Contents 1. Contents . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 2. List of Illustrations . . . . . . . . . . . . . . . . . . . . . . . .3 3. Technical Specifi cation . . . . . . . . . . . . . . . . . . . . . .4 4. Introduction . . . . . . . . . . . . .

2、. . . . . . . . . . . . . .7 5. Installation . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 6. Operation. . . . . . . . . . . . . . . . . . . . . . . . . . . .10 7. Brief Technical Description. . . . . . . . . . . . . . . . . . .14 8. Detailed Circuit Description . . . . . . . . . . . . .

3、. . . . . .16 9. Maintenance . . . . . . . . . . . . . . . . . . . . . . . . . . .25 10. Spurious Responses . . . . . . . . . . . . . . . . . . . . . . .26 11. Fault Diagnosis . . . . . . . . . . . . . . . . . . . . . . . . .28 12. Representative Test Data . . . . . . . . . . . . . . . . . . . .30 1

4、3. General Servicing and Aligment Procedures. . . . . . . . . .32 13.1. General Servicing. . . . . . . . . . . . . . . . . . . . . .33 13.2. Receiver Tests . . . . . . . . . . . . . . . . . . . . . . . .33 14. Alignment Procedures. . . . . . . . . . . . . . . . . . . . .37 14.1. Introduction. . . .

5、. . . . . . . . . . . . . . . . . . . .37 14.2. 100 kc/s I.F. Amplifi er. . . . . . . . . . . . . . . . . . . .37 14.3. 100 kc/s (L-C) Filter . . . . . . . . . . . . . . . . . . . . .37 14.4. Second V.F.O. . . . . . . . . . . . . . . . . . . . . . .39 15. Dismantling . . . . . . . . . . . . . . . .

6、. . . . . . . . . . .44 16. Component List 1. . . . . . . . . . . . . . . . . . . . . . .49 17. Component List 2 . . . . . . . . . . . . . . . . . . . . . . . .63 18. Valve Data. . . . . . . . . . . . . . . . . . . . . . . . . . .67 19. Illustrations . . . . . . . . . . . . . . . . . . . . . . . . .

7、 . .69 2 2. List of Illustrations Fig. Rear View of Receiver Chassis1 Front Panel, RA.1172 RA.117 Block Diagram3 Simplifi ed Balancing Circuit4 Noise Limiter Circuit5 Typical Selectivity Curves6 Terminal Tag Strip7 Top View of Receiver8 First V.F.O. - top view9 First V.F.O. - underside10 Second V.F.

8、O.11 1.7 Mc/s Oscillator/Amplifi er and Mixer Unit12 B.F.O. Unit13 Crystal Calibrator Unit14 Key to Under-chassis Layout15 R.F. Attenuator16 Supply Filters17 Crystal Oscillator/Amplifi er and Harmonic Filter System18 Second Mixer19 Band-Pass Filter20 100 Kc/s I.F. amplifi er - right side21 100 Kc/s

9、I.F. amplifi er - left side22 Power Supply and Audio Stages23 3 3. Technical Specifi cation Frequency range:1 30 Mc/s Stability:Afterwarm-up, overall drift is less than 50 c/s per hour under conditions of constant supply voltage and ambient temperature. Input impedance:(1) Wideband 2000-ohms approx.

10、 (2) Wideband 75 ohms. (3) 5 double-tuned circuits, 75 ohms. (a) 1 2 Mc/s (b) 2 4 Mc/s (c) 4 8 Mc/s (d) 8 16 Mc/s (e) 16 30 Mc/s Tuning: Eff ective scale lenght of approximately 145 feet, i.e. 6 inches of scale lenght corresponds to 100 kc/s Frequency increments remain constant over the entire range

11、. Calibration:A 100 kc/s signal derived from a 1 Mc/s crystal oscillator having an accuracy of 5 parts in 106provides check points at 100 kc/s intervals. Sensitivity:A1 reception, bandwidth 3 Kc/s; 1V for 18dB signal-to- noise ratio. A2 reception, 30% modulated, bandwidth 3 Kc/s; 3V for 18dB signal-

12、to-noise ratio. Intermodulation:More than 100dB down for interfering signals at least 10% removed from the wanted signal. Cross modulation:For wanted signal levels between 3V and 1mV, an inter- fering signal 10 Kc/s removed and modulated 30% must have a level greater than 50dB above that of the want

13、ed signal to produce a cross modulation of 3%. The ratio of wanted to unwanted signal is improved up to 10% off tune, at the rate of 3dB per cent. Blocking:With similar conditions to those for cross modulation an unwanted signal f2must be 60dB greater before the audio output of the wanted signal f1i

14、s reduced by 3dB due to blocking. Selectivity:Six alternative I.F. bandwitchs are obtained by means of a selector switch. Filter details are: -6dB-66dB (1)13 kc/s35 kc/s (2)6.5 kc/s22 kc/s (3)3.0 kc/s15 kc/s (4)1.2 kc/s8 kc/s (5)0.3 kc/sLess than 2 kc/s (6)0.1 kc/sLess than 1.5 kc/s 4 Technical Spec

15、ifi cation5 Bandwidths 5 and 6 are obtained with crystal-lattice fi l- ters; diff erences in centre frequencies of these bandwitdth settings do not exceed 50c/s. I.F. Output:100 kc/s at 75-ohms impedance. Level 0.2 V approx, with A.V.C. in operation. Two outlets in parallel are provided. Image and S

16、purious Responses: With wideband or tuned input, external image signals are at least 60dB down. Internally generated spurious re- sponses are less than 2dB above noise level in all cases. Noise Factor:Better than 7dB throughout entire range. B.F.O. Range:8 kc/s B.F.O. Stability:With constant ambient

17、 temperature and supply voltage, drift after warm-up does not exceed 50 c/s. For input level variations from 10V to 1mV, B.F.O. drift is negligible. Automatic Volume Control:An increase in signal level of 20dB above 1V improves the signal-to-noise ratio by 18dB. An increase in signal level of 100dB

18、above 1V increases the A.F. output by less than 7dB. A.V.C. Time Constants:Short:Charge25milliseconds Discharge200 milliseconds Long:Charge200 milliseconds Discharge1second A.F. Response:With 13 kc/s bandwidth, response remains within 4dB from 250 c/s to 600 c/s. A.F. Output:1. 2.5-in. loudspeaker o

19、n front panel (switched). 2. Two headphone sockets in parallel on front panel. (see Note) 3. Three independent outputs of 3mW at 600-ohms at rear of chassis. 4. One output of 10mW at 600-ohms. Preset level is independent of A.F.GAIN control setting. 5. One output of 1W at 3-ohms. Note: The two headp

20、hone sockets are connected across one of the 600-ohms, 3mW outlets. Distortion:Not greater than 5% at 1W output. Hum Level:With A.F.GAIN control at maximum, the hum level is never worse than 40dB below rated output (1W) Noise Limiter:A series noise limiter circuit van be switched into oper- ation to

21、 provide limiting at modulation levels exceeding 30%. Meter Indication:Alternative switching for indication of signal carrier level, A.F. output level or ”S” meter indication. Power Supply:100-125V and 200-250V, 45-65 c/s. Power consumption 100W approx. Technical Specifi cation6 Dimensions: HeightWi

22、dthDepth For rack mounting 10.5in19in20.125in (fi tted dust cover) 26.7cm48.25cm51cm. Fittedcabinet12in20.5in21.875in 30.5 cm52cm55.6cm Weight:Rack mounted62 lb (28 kg) In cabinet92 lb (42 kg) 4. Introduction General Description 1. The Communications Receiver Type RA.117 has been designed for use as

23、 a general purpose receiver which will provide a high order of selectivity and stability. The re- ceiver covers a frequency range from 1.0 to 30.0 Mc/s. 2. A built-in crystal-controlled calibrator provides reference signals at each 100 kc/s division to permit exact alignment of the scale pointer. Tw

24、o independent I.F. outputs, in parallel, at 100 kc/s are provided for external use if required. A number of audio outputs are available providing fl exibility during operation; a small loudspeaker is fi tted for monitoring purposes. 3. The receiver is designed to operate from 100-125 volts and 200-2

25、50 volts, 45-65 c/s main supply. The power consumtion is approximately 100 watts. Constructional Details 4. The receiver is designed for both bench (table) and rack mounting. The front panel is painted Light Battleship Grey (British Standard Specifi cation 381C, colour 697) and has been carefully de

26、signed to minimize operator fatigue. 5. The dimensions of the 1/8 in. thick front panel conform with the requirements for mounting in a standard 19 in. rack. 6. For bench mounting, the receiver is fi tted in a robust steel cabinet which has a rear opening to enable the operator to gain easy access t

27、o the fuses and the termination strips. 7.A dust cover is provided with both models. This may be removed from cabinet- mounted receivers in conditions of high ambient temperature. 8.The chassis and major modules are of cast construction thus ensuring maximum rigid- ity and eff ective electrical scre

28、ening. Each receiver is supplied with three keys to facil- itate removal of the control knobs, insulated trimming tool and coaxial terminations for aerial and I.F. connections. Extra sleeves can be provided with the terminations for alternative coaxial cable sizes. 7 Introduction8 5. Installation 1.

29、 After carefully unpacking the receiver, remove the dust cover and make sure that all valves and screening cans are fi rmly in place and that no packing material remains within the tuning mechanism. POWER SUPPLY. 2. Ascertain that the mains transformator is set to the appropriate voltage tapping. Th

30、is is carried out by means of soldered connections to the transformer. A power lead is permanently fi tted to the receiver which can be connected directly to the power supply. Check that the terminals HT1 and HT2 situated on the main chassis are linked (unless the L.F. Converter is in use). FUSES. 3

31、. Ensure that the rating of the supply fuse and the H.T. fuse correct wiz: Supply fuse2A H.T. fuse350mA, anti surge. AERIAL. 4. The impedance at the aerial (antenna) input plug is designed to match into a 75-ohms unbalanced transmission line. The cable termination supplied with the receiver can bee

32、provided with alternative sleeves to enable it to be used with a type UR.18 or UR.70 cable or similar cables of nominal diameter 1/2-in or 1/4-in. respectively. AUDIO OUTPUTS. 5.A number of audio outputs are available to give the following facilities. (1) The two telephone jack sockets situated on t

33、he front panel are connected across one of the 600 Ohms, 3mW outlets. (2) The following outputs are connected to the terminal strip at the rear of the receiver:- (a) Three 600-ohms outlets at 3mW. (b) One 3-ohm outlet at 1W. (c) One 600-ohms outlet at 10mW. This output is controlled by a preset A.F.

34、 LEVEL control on the front panel and is independent of the outputs previ- ously described. 100 kc/s I.F. OUTPUT. 6. The connection consists of two coaxial plugs connected in parallel to the 100 kc/s output. The total load should not be less than 75-ohms (e.g. with outlet loaded by 75-ohms, the othe

35、r can be can used as a high impedance source). EXTERNAL INPUT/OUTPUT CONNECTIONS. 7. The following input and output connections are available on a panel at the rear of the receiver (fi g.1):- 9 Installation10 1 Mc/s input/output:May be used diversity operation. 2nd V. F. O. output/input(3.6 4.6 Mc/s

36、)For diversity operation and external chan- nelizer crystal oscillator output. 1.7 Mc/s input/output For diversity operation and fi ne tuning unit input. R.F. (2 3 Mc/s) input:Input from an L.F. converter. The above input/output connections are selected by internal linkage, the connections should be

37、 made as follows:- 1 Mc/s inputRemove “T” adaptor and place in clip pro- vided on side of gusset plate. Connect the free plugs PL12 to SKT3 and connect the free plug PL2 to SKT2. 1 Mc/s outputDisconnect plugs PL12 and PL2 and con- nect “T” adaptor to socket SKT2. Connect plugs PL12 and PL2 to the “T

38、” adaptor. 2nd V.F.O. inputConnect the free plug PL302 to SKT302. 2nd V.F.O. outputConnect the free plug PL303A to SKT304. 1.7 Mc/s inputConnect the free plug PL303A to SKT303. 1.7 Mc/s outputConnect the free plug PL303A to SKT306. (blue) Note 1 When using the internal oscillators with crystals, the

39、 connections should be made for outputs since the cable capacity will pull the internal crystal off frequency. Note 2 The 1 Mc/s and 1.7 Mc/s crystal must be removed if an external source is applied to the input socket. Stowage space is provided on the chassis for the crystals when they are not in u

40、se. AUTOMATIC VOLUME CONTROL. 8. The A.V.C. line is brought out to the terminal strip at the rear of the chassis for such applications as diversity reception. Installation11 6. Operation 1. References to the controls are in capitals and are in accordance with the panel titles adjacent to them (fi g.

41、2). 2. It should be noted that the method of operation of the receiver extremely simple, depens largerly upon the purpose for which the receiver is being embloyed. FUNCTION OF CONTROLS. 3. The front panel controls are described in the order in which they could be used for setting-up prior to use. PO

42、WERMakes and breaks the power supply to the mains transformer. R.F. RANGE MC/S This control enables the selection of one any of fi ve antenna ranges plus two WIDEBAND positions, one of 75-ohms input impedance and other a high impedance input of 2000-ohms. R.F. ATTENUATORThis control enables the oper

43、ator to reduce the level of all incoming signals when strong unwanted signals are present which cannot be rejected suffi ciently by tuning the antenna. MEGACYCLESThis control selects the desired Mc/s frequency. The dial should be checked periodically to ensure that its setting is reasonably central

44、with respect to the band in use. This is indicated by a reduction of signal or noise on either side of the correct setting. SYSTEMThis switch provides facilities for STANDBY, MANUAL, A.V.C., CALIBRATION and CHECK B.F.O. BANDWIDTH The two crystal fi lters determining the band- width are adjusted to e

45、nsure that their centre frequencies are all within 50 c/s, thus any bandwidth can be selected without retuning the receiver. Six bandwidths are provided as follows:- 13 kc/s, 6.5 kc/s, 3 kc/s and 1.2 kc/s (L-C) 300 c/s and 100 c/s (crystal) A.F. GAINThe A.F. GAIN control adjusts the audio output. KI

46、LOCYCLESThis control selects the desired kc/s frequency. The calibration of this scale may be checked at 100 kc/s intervals by setting the system switch to the CAL. position and V.F.O. switch set to INT. B.F.O.The B.F.O. ON/OFF switch makes or breaks H.T. to the beat frequency oscillator. B.F.O. NOT

47、E KC/SThe B.F.O. is exatly tuned to a central point on the I.F. ampli- fi er response when B.F.O. NOTE KC/S control is st to zero-beat with the calibrator. Having standardized the B.F.O. frequency, the frequency of an incoming signal may be accurately measured by set- ting the KILOCYCLES control to

48、a zero-beat position; the B.F.O. should de detuned in order to produce an acceptaple note for c.w. reception. 12 Operation13 R.F. TUNEIf maximum sensitivity is not required, the antenna need not be tuned unless strong unwanted signals are present. It should be noted that the presence of very strong

49、singnals anywhere within the spectrum may cause crossmodulation unless the aerial is tuned. Under these conditions, CARE MUST BE TAKEN TO AVOID TUNING THE INPUT TO THE INTERFERING SIGNALS in- stead of the signal required. Familiarity with the tuning controls will facilitate this. R.F./I.F. GAINThe R.F./I.F. GAIN control is operative both in the MAN. and the A.V.C. position of the SYSTEM switch. In the MAN.position of the SYSTEM switch the setting of the control should be always at a minimum consistent with satisfactory A.F. level. The following should be noted when the SY