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Racal Instruments RA-117 User Manual

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Racal RA-117
Radio Receiver

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Summary of Contents for Racal Instruments RA-117

  • Page 1 Racal RA-117 Radio Receiver...

  • Page 2: Table Of Contents

    1. Contents 1. Contents ......2. List of Illustrations ......3.

  • Page 3: List Of Illustrations

    2. List of Illustrations Fig. Rear View of Receiver Chassis Front Panel, RA.117 RA.117 Block Diagram Simplified Balancing Circuit Noise Limiter Circuit Typical Selectivity Curves Terminal Tag Strip Top View of Receiver First V.F.O. - top view First V.F.O. - underside Second V.F.O.

  • Page 4: Technical Specification

    3. Technical Specification 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. (2) Wideband 75 ohms. (3) 5 double-tuned circuits, 75 ohms. (a) 1 –...

  • Page 5: Noise Limiter Circuit

    Technical Specification Bandwidths 5 and 6 are obtained with crystal-lattice fil- ters; differences 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 Spurious Responses: With wideband or tuned input, external image signals are at least 60dB down.
  • Page 6 Technical Specification Dimensions: Height Width Depth For rack mounting 10.5in 19in 20.125in (fitted dust cover) 26.7cm 48.25cm 51cm. Fitted cabinet 12in 20.5in 21.875in 30.5 cm 52cm 55.6cm Weight: Rack mounted 62 lb (28 kg) In cabinet 92 lb (42 kg)

  • Page 7: Introduction

    4. Introduction General Description 1. The Communications Receiver Type RA.117 has been designed for use as 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.

  • Page 8: Installation

    5. Installation 1. After carefully unpacking the receiver, remove the dust cover and make sure that all valves and screening cans are firmly 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. This is carried out by means of soldered connections to the transformer.
  • Page 9 Installation 1 Mc/s input/output: May be used diversity operation. 2nd V. F. O. output/input(3.6 – 4.6 Mc/s) For diversity operation and external chan- nelizer crystal oscillator output. 1.7 Mc/s input/output For diversity operation and fine tuning unit input. R.F. (2 – 3 Mc/s) input: Input from an L.F.

  • Page 10: Operation

    6. Operation 1. References to the controls are in capitals and are in accordance with the panel titles adjacent to them (fig.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.
  • Page 11 Operation R.F. TUNE If 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 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.
  • Page 12 Operation PRELIMINARY SETTING-UP. 4. The instructions given below are concerned with tuning the receiver to a signal of known frequency. These instructions (1) to (8) apply with the V.F.O. switch in either position. (1) Set the power switch to ON. Allow a few minutes for the receiver to warm-up. (2) Set the R.F.
  • Page 13 Operation (13) Set KILOCYCLES scale to the required frequency and critically tune for zero beat in order to centralize the signal within the I.F. pass-band. (14) Adjust R.F. TUNE for maximum signal (or noise). For optimum c.w. reception, “off-tune” the B.F.O. to produce an acceptaple beat note. (15) Set the A.F.

  • Page 14: Brief Technical Description

    7. Brief Technical Description 1. This section describes briefly, with the aid of the block diagram fig. 3, the basic theory of operation. For a more detailed explanation of the receiver, DETAILED CIRCUIT DESCRIPTION, should be consulted. SIGNAL INPUT 2. The receiver is designed for an input impedance of 75-ohms for all positions of the R.F.
  • Page 15 Brief Technical Description 9. Frequency drift of VFO-1 within the limits of the 37 5 Mc/s filter bandwidth, does not affect the frequency stability of the receiver. A change in this oscillator frequency will alter the first I.F. to the same extent and in the same sense as the nominal 37 5 Mc/s signal from the harmonic mixer.

  • Page 16: Detailed Circuit Description

    8. Detailed Circuit Description 1. Reference should be made to the circuit diagram at the end of this handbook. AERIAL CIRCUIT 2. A 75-ohms unbalanced aerial source is connected to the tuned R.F. amplifier through a three-section 30 Mc/s low-pass filter and a five- position attenuator covering a range of 0 to 40 dB.
  • Page 17 Detailed Circuit Description FIRST MIXER (M1) 6. The outputs from the 30 Mc/s low-pass filter and the variable frequency oscillator VFO-1 are fed to the signal grid of the mixer stage (V7) which produces a signal at 40 Mc/s. The signal is then passed to a 40 Mc/s band-pass filter which forms the anode load of this stage.
  • Page 18 Detailed Circuit Description core L33. This stage feeds the amplified signal via C68 to the following stage V8. The 37.5 Mc/s signal is then passed to the 37.5 Mc/s band-pass filter. The anode load of this stage is provided by this filter. 37.5 MC/S BAND-PASS FILTER 14.
  • Page 19 Detailed Circuit Description SECOND VARIABLE FREQUENCY OSCILLATOR (VFO-2) 20. The second variable frequency oscillator, covering a frequency range 3 6 to 4 6 Mc/s, is an electron coupled Hartley circuit embloying one half of double-triode V12. The oscillator frequency is determined by an inductance L55, two fixed capacitors C303, C305, a trimming capacitor C306 and a variable capcitor C301.
  • Page 20 Detailed Circuit Description and L63 in series with C152, C152A and C153. The final section consisting of L68 and L71 in series with C161 and C162, is damped by the series resistors R86, R87A and R88 according to the bandwidth. In the L-C positions the output is taken from a capacitive divider formed by C161 and C161A with C170, to equalize the gains in the L-C and crystal bandwidth positions.
  • Page 21 Detailed Circuit Description at B, will be lower than at A and will be maintained at a constant level due to the long time constant of R134 and C217. R135 allows the cathode potential to vary in sympathy with the modulation provided the modulation depth does not exceed 30%. The potential appearing at the cathode of the noise limiter diode therefore consists of a steady negative potential with the modulation superimposed.
  • Page 22 Detailed Circuit Description produce an output frequency of preisely 100 kc/s when the beat frequency oscillator frequency control is set to zero. Bias is applied to this valve by C199 and R125. 39. The B.F.O. output is coupled to the diode detector anode via C215. The B.F.O. is supplied with H.T.
  • Page 23 Detailed Circuit Description R124 is connected between the negative line and earths thus providing a negative 25V d.c. supply for gain control purposes. SYSTEM SWITCH 45. The following conditions exist for each setting of the SYSTEM switch. The link on H.T.
  • Page 24 Detailed Circuit Description at maximum is the correct calibration maintained.

  • Page 25: Maintenance

    9. Maintenance WARNING! The receiver will, under normal conditions, remain in align- ment over an extremely long period time, consequently ALL POSSIBIL- ITY OF OTHER CAUSES OF LOW SENSITIVITY SHOULD BE ELIM- INATED BEFORE RE-ALIGNMENT IS CONSIRED, and should then only be undertaken by order of the Engineer responsible for the mainte- nance of the equipment.

  • Page 26: Spurious Responses

    10. Spurious Responses ORIGINS OF SPURIOUS RESPONSES 1. In a high sensitive receiver, precautions against internally generated spurious responses are essential. To this end, various sections of the receiver have been carefully screened and the power supplies filtered. 2. Any reduction in the screening efficiency or the failure of any filtering component may results in spurious signals being generated.
  • Page 27 Spurious Responses 6 MC/S BREAK-THROUGH 5. When the receiver is tuned to 3 2 Mc/s the first v.f.o. frequency is 43 5 Mc/s. This reaches the second mixer and combines with 37 5 Mc/s giving a stable 6 Mc/s which may pass through the 2 3 Mc/s BPF where it combines with the second v.f.o.

  • Page 28: Fault Diagnosis

    11. Fault Diagnosis INTRODUCTION 1. The following notes and test procedures enable the faulty section of the receiver to be determined with the minimum of delay. Unless other- wise stated the meter on the front panel is used for measuring purposes. This is set to R.F. LEVEL and the reference figure is 100 A for all sensitivity tests.
  • Page 29 Fault Diagnosis Fourth mixer First I.F. amplifier Second I.F. amplifier 1.7 Mc/s oscillator/amplifier 8. Set BANDWIDTH control to 3 kc/s. Refit the 1.7 Mc/s crystal XL300. Connect the output of the signal generator to socket SKT301 (pink) and tune the generator to a frequency of 1.6 Mc/s.

  • Page 30: Representative Test Data

    12. Representative Test Data Signal Input to: Frequency Input Output Remarks (a) Junction of 1,000 c/s 0 8V 50mW in 3 ohms AUDIO GAIN MAX. A.F. LEVEL MAX. C218 and C221B 1,000 c/s 1 0V 10mW in 600 ohms R.F. & I.F. GAIN (output to line) MIN.
  • Page 31 Representative Test Data 2 volts. (h) The level of the 37 5 Mc/s drive at TP3 should be between 2 and 10 volts at any MEGACYCLES setting.
  • Page 32 [32]...

  • Page 33: General Servicing And Aligment Procedures

    General Servicing and Aligment Procedures 13. General Servicing and Aligment Procedures 13.1. General Servicing INTRODUCTION 1. The following tests will assist in checking the performance of the receiver. 2. Component layout illustrations, fig.8 to fig.23 inclusive, give an overall picture of the receiver sub-assemblies and chassis underside.
  • Page 34 General Servicing and Aligment Procedures SIGNAL-TO-NOISE TEST 7. Perform a signal-to-noise test as follows:- (1) Set the receiver controls as follows:- R.F. RANGE 1 – 2 Mc/s MEGACYCLES KILOCYCLES R.F. ATTENUATOR MIN. SYSTEM switch MAN. BANDWIDTH 3 kc/s B.F.O. switch B.F.O.
  • Page 35 General Servicing and Aligment Procedures (3) Set the controls of the signal generator for a 30% modulated signal of 1 V at 3.5 Mc/s and an impedance of 75 ohms. Connect the signal generator output to the receiver antenna input socket. (4) Tune the receiver to the output frequency of the signal generator and adjust A.F.
  • Page 36 General Servicing and Aligment Procedures (7) Set the noise generator RANGE switch to 0 – 10. (8) Adjust the noise generator output level control until a reading of 20mW is ob- tained on the output meter. (9) The noise factor of the receiver is given by the noise generator meter reading for the range in use.

  • Page 37: Alignment Procedures

    14. Alignment Procedures 14.1. Introduction 11. The receiver will, under normal conditions, maintain the factory alignment over an ex- tremely long period of time. Consequently ALL POSSIBILITY OF OTHER CAUSES OF TROUBLE SHOULD BE ELIMINATED BEFORE RE-ALIGNMENT IS CON- SIDERED. 12.
  • Page 38 Alignment Procedures for an output of 200 V approximately for 100 A on front panel meter. Check that the bandwidths agree (approximately) with the folowing figures:- -6dB -66dB Sensitivity for 100 A 3.0 kc/s 15 kc/s Less than 200 V (Measured in- put becomes reference level) 100 c/s Less than 1.5 kc/s...

  • Page 39: Second V.f.o

    Alignment Procedures from signal generators. A digital frequency meter should therefore be employed. The equipment should be connected to SK8 or SK9. The exact frequency passing through the circuit will be displayed on the indicator panel. Should the level of output at any time during the alignment procedure be insufficient to drive the frequency meter, the signal generator output can be increased to obtain the frequency check but must be restored to the lower value for level measurements.
  • Page 40 Alignment Procedures (2) Check the calibration of the v.f.o. at 100 kc/s intervals; if the error exceeds 1 kc/s, adjust carefully the plates of the rotor of the variable capacitor in order to correct the calibration. 1 6 Mc/s Rejection Filter 26.
  • Page 41 Alignment Procedures stop. Check that the mechanical stops operate before the capacitor end-stops become effective at both ends of the band. 34. To re-adjust the first v.f.o. calibration, a heterodyne wavemeter should be employed. This is Coupled very loosely to V7 by placing its input lead in the vicinity of the valve base.
  • Page 42 Alignment Procedures Table 1 R.F. RANGE INDUCTOR ALIGNMENT TRIMMER ALIGNMENT FREQUENCY FREQUENCY 2 - 4 2 Mc/s C234 4 Mc/s 4 - 8 4 Mc/s C235 8 Mc/s 8 - 16 8 Mc/s C236 16 Mc/s 16 - 30 13 Mc/s (C18 at C237 max.) 30 Mc/s Table 2...
  • Page 43 Alignment Procedures 1 6 Mc/s Band-pass Filter 50. To carry out alignment of this filter, the mixer chassis must first be removed. After the removal of the chassis, turn the receiver on to its side and reconnect, from the underside, the two leads (6.3V and 200V H.T.) to their respective pins. 51.

  • Page 44: Dismantling

    15. Dismantling Unit Breakdown 1. The receiver may be rapidly dismantled to eight sub-units as follows:- (1) Front Panel (a) Tuning escutcheon. (b) Loudspeaker and escutcheon. (c) Output level meter. (2) Second Variable Frequency Oscillator (a) Second v.f.o. (V12). (3) First Variable Frequency Oscillator (a) R.F.
  • Page 45 Dismantling NOTE: The two screws at the bottom of the front panel, adjacent to the jack sockets, are secured to the main chassis with nuts. (3) Carefully withdraw the front panel and unsolder the connections to the meter and speaker switches; alternatively, the number of wires to be unsoldered can be minimized (loudspeaker only) by removing the seciring nuts on the SPEAKER and METER switches.
  • Page 46 Dismantling (3) Hold the two gear wheels at the top of the right-hand film bobbin against the spring tension and remove the two screws securing the idler gear mounting as- sembly. (4) Ease the idler gear clear of the film bobbin gear wheels and carefully ease the spring tension from them.
  • Page 47 Dismantling (2) Unsolder the connecting wires from the two turret lugs situated in compartment 8, the leads to the turret lug in compartement 6, the pin connections compartment 2 and the screened cable compartment 1. (3) Unscrew the three fixing screws on the top of the unit. (1) Fitting a new chain:- (a) Take a 63-link lenght of chain.
  • Page 48 Dismantling (3) Disconnect the coaxial cables. (4) Remove the three screws securing this unit to the main chassis. (5) Re-assemble in the reverse order. Valve Replacement 12. With the exception of V5, replacement of valves will not affect receiver alignment. When V5 is replaced refer to GENERAL SERVICING AND ALIGNMENT PROCE- DURES.

  • Page 49: Component List

    16. Component List 1. Resistors Cct. Value Description Rat. Tol. Ref. carbon 1/4W 100ohm carbon 1/4W 150ohm carbon 1/4W 100ohm carbon 1/4W 150ohm carbon 1/4W 4.7Kohm carbon 1/2W 150ohm carbon 1/4W 150ohm carbon 1/4W 47Kohm carbon 1/4W 680ohm carbon 1/4W 220ohm carbon 1/2W...
  • Page 50 Component List 1. R32A 100Kohm carbon 1/4W R32B 10Kohm carbon 1/4W 10Kohm carbon 1/4W 470Kohm carbon 1/4W DELETED 10ohm carbon 1/4W 1Kohm carbon 1/4W 68ohm carbon 1/4W 22Kohm carbon 1/4W 10ohm carbon 1/4W 10Kohm carbon 1/4W 27Kohm carbon 1/2W 6.8Kohm carbon 1/4W 27Kohm...
  • Page 51 Component List 1. DELETED DELETED 150ohm carbon 1/4W DELETED DELETED 470Kohm carbon 1/4W DELETED 2.2Kohm carbon 1/4W 470Kohm carbon 1/4W 2.2Kohm carbon 1/2W R81A 1.5Kohm carbon 1/4W R81B 10Mohm carbon 1/4W R81C 10Mohm carbon 1/4W DELETED 4.7Kohm carbon 1/4W 1Mohm carbon 1/4W 220ohm...
  • Page 52 Component List 1. R110 100ohm carbon 1/4W R111 2.2Kohm carbon 1/2W R112 47Kohm carbon 1/4W R113 33Kohm carbon 1/2W R114 100ohm carbon 1/4W R115 150ohm carbon 1/4W R116 470Kohm carbon 1/4W R116A 6.8Kohm carbon 1/4W R117 150ohm carbon 1/4W R118 2.2Mohm carbon 1/4W...
  • Page 53 Component List 1. R144A 10ohm carbon 1/4W R300 820ohm carbon 1/2W R300A 220ohm carbon 1/4W R301 100Kohm carbon 1/4W R302 47ohm carbon 1/4W R303 33Kohm carbon 1/4W R304 220ohm carbon 1/4W R305 1.5Kohm carbon 1/4W R306 4.7Kohm carbon 1/4W R307 470Kohm carbon 1/4W...
  • Page 54 Component List 1. Capacitors Cct. Value Description Rat. Tol. Ref. 2.7pF Ceramic 750V DELETED 33pF Trimmer 10pF Silver/Mica 350V 0.01 F Paper 500V 0.01 F Paper 400V 14.7pF Ceramic 750V 14.7pF Ceramic 750V 14.7pF Ceramic 750V 10pF Trimmer 10pF Ceramic 750V 0.001 F Ceramic...
  • Page 55 Component List 1. 0.001 F Ceramic 350V 0.001 F Ceramic 350V 10pF Ceramic 750V 10pF Ceramic 750V 16pF Trimmer, 1000V with acetate case 39pF Silver/Mica 350V 16pF Trimmer, 1000V with acetate case 33pF Silver/Mica 350V 0.001 F Ceramic 350V 0.001 F Ceramic 350V 0.1 F...
  • Page 56 Component List 1. 0.001 F Ceramic 350V 0.001 F Ceramic 350V 16pF Trimmer, 1000V with acetate case 39pF Silver/Mica 350V 16pF Trimmer, 1000V with acetate case 33pF Silver/Mica 350V 0.001 F Ceramic 350V 0.001 F Ceramic 350V 100pF Silver/Mica 350V 220pF Silver/Mica 350V...
  • Page 57 Component List 1. 33pF Silver/Mica 350V 16pF Trimmer, 1000V acetate case 15pF Silver/Mica 350V 0.001 F Ceramic 350V 0.001 F Ceramic 350V 0.001 F Ceramic 350V 0.01 F Paper 500V C95A 0.001 F Ceramic 350V 0.001 F Ceramic 350V 0.25 F Paper 150V 0.01 F...
  • Page 58 Component List 1. C128 DELETED C129 DELETED C130 0.001 F Ceramic 350V C130A 0.01 F Paper 500V C131 0.001 F Ceramic 350V C132 0.001 F Ceramic 350V C133 0.001 F Ceramic 350V C134 DELETED C135 DELETED C136 DELETED C137 DELETED C138 DELETED C139...
  • Page 59 Component List 1. C159 0.05 F Paper 350V C159A 0.1 F Paper 150V C159B 0.001 F Ceramic 350V C160 0.05 F Paper 350V C161 290pF Silver/Mica 350V C161A 100pF Ceramic 750V C162 70pF Trimmer, 12 vane with acetate case C163 0.05 F Paper 350V...
  • Page 60 Component List 1. with acetate case C192 390pF Silver/Mica 350V C193 100pF Ceramic 750V C193A 0.001 F Ceramic 350V C194 0.1 F Paper 150V C194A 0.001 F Ceramic 350V C195 0.1 F Paper 350V C195A 390pF Silver/Mica 350V C195B 70pF Trimmer, 12 vane with acetate case...
  • Page 61 Component List 1. C221A Electrolytic 350V C221B 68pF Silver/Mica 350V C222 50 F Electrolytic C222A 0.001 F Ceramic 350V C222B 0.05 F Paper 350V C223 DELETED C224 0.01 F Silver/Ceramic 750V C225 0.01 F Silver/Ceramic 750V C226 82pF Silver/Ceramic 750V C227 82pF Silver/Ceramic...
  • Page 62 Component List 1. C321 0.01 F Paper 500V C321A 0.001 F Silver/Mica 350V C322 300pF Silver/Mica 350V C323 0.01 F Paper 250V C234 15pF Silver/Mica 350V C235 100pF Silver/Mica 350V C326 0.001 F Silver/Mica 350V C327 0.001 F Silver/Mica 350V C328 53pF Silver/Mica...

  • Page 63: Component List

    17. Component List 2 Valves Pentode CV4010 6AK5W Pentode CV4010 6AK5W Double-Triode CV5331 6ES8/ECC189 Pentode CV4011 6AS6 Pentode CV4009 6BA6 Pentode CV4009 6BA6 Pentode CV3998 6688/E180F Pentode CV4009 6BA6 Pentode CV3998 6688/E180F Pentode CV4009 6BA6 Pentode CV4010 6AK5W Double-Triode CV4024 12AT7 Heptode CV4012...
  • Page 64 Component List 2 Filter detail assembly Common assembly wth L13 Common assembly with L1 Common assembly with L13 Common assembly with L1 Common assembly with L13 Common assembly with L13 First V.F.O. anode coil (assy with R18) Common assembly with L13 Common assembly with L13 40 Mc/s filter 37 5 Mc/s filter...
  • Page 65 Component List 2 DELETED DELETED DELETED DELETED First L-C filter stage Common assembly with L61 Second L-C filter stage Common assembly with L63 Choke DELETED Third L-C filter stage Common assembly with L67 0 1 Mc/s coupling coil Common assembly with L69 Final L-C filter stage ) 100 kc/s I.F.
  • Page 66 Component List 2 L330 Coil Assembly Transformers Mains Audio Output A.F. Line Output Rectifiers Meter Rectifier, 1mA Rectifier Rectifier Rectifier Rectifier Loudspeakers 2 1/4 inch square 3 ohm Meter 200 micro-amp. Crystals 1 Mc/s 0.005% 99,964 c/s 0.005% 99,890 c/s 0.005% DELETED 100,036 c/s...

  • Page 67: Valve Data

    18. Valve Data INTRODUCTION 1. Details of valves used in the receiver are given in Tables 1 and 2 overleaf. The location of valves is shown in fig. 8 and valve base connections are given in the circuit dia- gram. Voltages were obtained from a B9A or B7G stand-off valve base using a 20,000 ohms/volt meter on the optimum range in each case.
  • Page 68 Valve Data 195(5) 85(6) 0.95(2) 6BA6 EF93 37.5 Mc/s amplifier 168(7) 135(9) 0.86(1) 6688 E180F Second mixer 205(5) 108(6) 2.06(2) 6BA6 EF93 37.5 Mc/s amplifier 155(5) 110(6) 1.95(2) 6AK5W M8100 Second v.f.o. amplifier 100(6) 12AT7 ECC81 Second v.f.o. 195(1) 44(3) 225(5) 90(6) 2.0(2)

  • Page 69: Illustrations

    19. Illustrations Fig. Top View of Receiver First V.F.O. - top view First V.F.O. - underside Second V.F.O. 1.7 Mc/s Oscillator/Amplifier and Mixer Unit B.F.O. Unit Crystal Calibrator Unit Key to Under-chassis Layout R.F. Attenuator Supply Filters Crystal Oscillator/Amplifier and Harmonic Filter System Second Mixer Band-Pass Filter 100 Kc/s I.F.
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