RACAL RA.117 MANUAL RACAL RA.117 SERVICE MANUAL 9.8.1999 TECHNICAL SPECIFICATION INTRODUCTION INSTALLATION OPERATION BRIEF TECHNICAL DESCRIPTION DETAILED CIRCUIT DESCRIPTION MAINTENANCE SPURIOUS RESPONSES VALVE DATA FAULT DIAGNOSIS REPRESENTATIVE TEST DATA GENERAL SERVICING AND ALIGNMENT PROCEDURES DISMANTLING COMPONENT LIST 1 (RESISTORS, CAPACITORS, SWITCHES, PLUGS AND SOCKETS) COMPONENT LIST 2 (VALVES, CRYSTALS, INDUCTANCES, TRANSFORMATORS ETC.) LIST OF ILLUSTRATIONS: FIG.1 - REAR VIEW OF RECEIVER CHASSIS FIG.2 - FRONT PANEL, RA.117 FIG.3 - RA.117 BLOCK DIAGRAM FIG.4 - SIMPLIFIED BALANCING CIRCUIT FIG.5 - NOISE LIMITER CIRCUIT RACAL RA.117 MANUAL FIG.6 - TYPICAL SELECTIVITY CURVES FIG.7 - TERMINAL TAG STRIP FIG.8 - TOP VIEW OF RECEIVER FIG.9 - FIRST V.F.O. - TOP VIEW FIG.10 - FIRST V.F.O. - UNDERSIDE FIG.11 - SECOND V.F.O. FIG.12 - 1.7Mc/s OSCILLATOR / AMPLIFIER AND MIXER UNIT FIG.13 - B.F.O. UNIT FIG.14 - CRYSTAL CALIBRATOR UNIT FIG.15 - KEY TO UNDER - CHASSIS LAYOUT FIG.16 - R.F. ATTENUATOR FIG.17 - SUPPLY FILTERS FIG.18 - CRYSTAL OSCILLATOR / AMPLIFIER AND HARMONIC FILTER SYSTEM FIG.19 - SECOND MIXER FIG.20 - BAND - PASS FILTERS FIG.21 - 100 kc/s I.F. AMPLIFIER - RIGHT SIDE FIG.22 - 100 kc/s I.F. AMPLIFIER - LEFT SIDE FIG.23 - AUDIO STAGES AND POWER SUPPLIES RA.117 RECEIVER - SCHEMATIC DIAGRAM BACK TO RECEIVERS AND SCHEMATICS ! BACK TO TECHNICAL INDEX (FINNISH) ! BACK TO RA.117-RECEIVER PAGE (FINNISH) ! RACAL RA.117 SPECIFICATIONS TECHNICAL SPECIFICATION RACAL Type RA117 ----------------------------TECHNICALSPECIFICATION ----------------------------------------------------------------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 - 2 Mc/s (b) 2 - 4 Mc/s (c) 4 - 8 Mc/s (d) 8 - 16 Mc/s (e) 16 - 30 Mc/s Tuning: Effective 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. Calibration: A 100 kc/s signal derived from a 1 Mc/s crystal oscillator having an accuraty of 5 parts in 10/6 provides check points at 100 Kc/s intervals. Sensitivity: A1 reception, bandwidth 3 Kc/s; 1µV for 18dB signal-to-noise ratio. A2 reception, 30% modulated, bandwidth 3 Kc/s; 3µV for 18dB signal-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 3µV and 1mV, an interfering signal 10 Kc/s removed and modulated 30% must have a level greater than 50dB above that of the wanted signal to produce a cross modulation of 3%. The ratio of wanted to unwanted signal is RACAL RA.117 SPECIFICATIONS improved up to 10% off tune, at the rate of 3dB per cent. Blocking: With similar conditions to those for cross modulation and unwanted signal f2 must be 60dB greater before the audio output of the wanted signal f1 is reduced by 3dB due to blocking. Selectivity: Six alternative i.f. bandwitchs are obtained by means of a selector switch. Filters detail are: -6dB -66dB (1) 13 kc/s 35 kc/s (2) 6.5 kc/s 22 kc/s (3) 3.0 kc/s 15 kc/s (4) 1.2 kc/s 8 kc/s (5) 0.3 kc/s Less than 2 kc/s (6) 0.1 kc/s Less than 1.5 kc/s Bandwidths 5 and 6 are obtained with crystal-lattice filters; differences in centre frequencies of these bandwitdth settings do not exceed 50c/s. I.F. ouput: 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 With wideband or tuned input, external image signals responses: are at least 60dB down. Internally generated spurious responses are less than 2dB above noise level in all cases. Noise factor: Better than 7dB troughout entire range. B.F.O. range: ±8 kc/s B.F.O. stability: With constant ambient temperature and supply voltage, drift after warm-up does not exceed 50 c/s. For input level variations from 10µV to 1mV, b.f.o. drift is negligible. Automatic volyme An increase in signal level of 20dB above 1µV control: improves the signal-to-noise ratio by 18dB. An increase in signal level of 100dB above 1µV increases the a.f. output by less than 7dB. A.V.C. time constans: Short: Charge - 25 milliseconds. Discharge - 200 milliseconds Long: Charge - 200 milliseconds Discharge - 1 second RACAL RA.117 SPECIFICATIONS A.F. response: With 13 kc/s bandwidth, response remains within ±4dB from 250 c/s to 600 c/s. A.F. output: 1. 2½-in. loudspeaker on 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 headphone 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 operation to 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. Dimensions: Height Width Depth For rack mounting 10½ 19 20.1/8 in. (fitted dust cover) 26.7 48.25 51 cm. Fitted cabinet 12 20.½ 21.7/8 in. 30.5 52 55.6 cm. Weight: Rack mounted 62 lb. (28 kg). In cabinet 92 lb. (42 kg). RACAL RA.117 INTRODUCTION 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 receiver 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. Two 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 flexibility during operation; a small loudspeaker is fitted for monitoring purposes. 3. The receiver is designed to operate from 100-125 volts and 200-250 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 Specification 381C, colour 697) and has been carefully designed to minimize operator fatique. 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 fitted in a robust steel cabinet which has a rear opening to enable the operator to gain easy acces to 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 rigidity and effective electrical screening. Each receiver is supplied with three keys to facilitate 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. RACAL RA.117 INTRODUCTION RACAL RA.117 OPERATION 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. 3. The front panel controls are described in the order in which they could be used for setting-up prior to use. POWER Makes and breaks the power supply to the mains transformer. R.F. RANGE MC/S This control enables the selection of one any of five antenna ranges plus two WIDEBAND positions, one of 75-ohms input impedance and other a high impedance input of 2000-ohms. R.F. ATTENUATOR This control enables the operator to reduce the level of all incoming signals when strong unwanted signals are present which cannot be rejected sufficiently by tuning the antenna. MEGACYCLES This cntrol selects the desired Mc/s frequency. The dial should be checked periodically to ensure that its setting is reasonably central with respect to the band in use. This is indicated by a reduction of signal or noise on either side of the correct setting. SYSTEM This switch provides facilities for STANDBY, MANUAL, A.V.C., CALIBRATION and CHECK B.F.O. BANDWIDTH The two crystal filters determining the bandwidth are adjusted to ensure 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:- RACAL RA.117 OPERATION 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. GAIN The A.F. GAIN control adjust the audio output. KILOCYCLES This 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. NOTE KC/S The b.f.o. is exatly tuned to a central point on the i.f. amplifier 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 setting the KILOCYCLES control to a zero-beat position; the b.f.o. should de detuned in order to produce an acceptaple note for c.w. reseption. 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 instead of the signal required. Familiarity with the tuning controls will facilitate this. R.F./I.F. GAIN the 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 SYSTEM switch is in the A.V.C. position. Reducing the i.f. gain results in a reduction of a a.v.c. loop gain together with the a degraded a.v.c. characteristic. Therefore when in the A.V.C. position, it is desirable that the R.F./I.F. GAIN control be set to maximum. A possible execption of this occurs when receiving interrupted signals in which the carrier is periodically switched off; in this case , receiver noise could be trouble- RACAL RA.117 OPERATION some during the quiet intervals. A.V.C. The choice of time-constant depens conditions. The LONG time-constant (1 second) should be employed with the choice signals, the SHORT time-constant may be used with high speed telegraphy or voice. For hand (low) speed telegraphy, the MAN. position of the SYSTEM switch should be used (refer to R.F./I.F. GAIN) A.F. LEVEL The preset control sets the a.f. level in a separate a.f. stage for feeding a 600-ohms, 10mW line. It is unaffected by the position of the main A.F. GAIN control. IT IS MOST IMPORTANT that the A.F. LEVEL is not turned towards its maximum position unless the 10mW 600-ohms winding is suitable terminated. LIMITER When swithced into use, the LIMITER reduces the effects of noise peaks exceeding the level of a 30% modulated signal. It does not introduce noticeable distortion below a 30% modulation level. "S" METER With the METER switch in the R.F. LEVEL position the meter indicates the signal diode current. In the A.F. LEVEL position, the 10mW, 600-ohms output only is monitored. A calibration mark is provided at 10mW. SPEAKER The loudspeaker may be switched ON or OFF as required. The two telephone jack sockets remain in circuit in either position of the SPEAKER switch. The insertion of a telephone jack disconnects the loudspeaker. V.F.O. This switch should be set to the EXT. position when a external 3.6-4.6 Mc/s source is applied. 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. RANGE MC/S switch to WIDEBAND. (3) Set R.F. ATTENUATOR to MIN. RACAL RA ...