DRAKE MODEL SPR-4 COMMUNICATIONS RECEIVER TECHNICAL MANUAL
Table of Contents 1. 1.1 1.2 GENERAL DESCRIPTION Features Specifications 1 1 2. 2.1 2.2 2.3 2.4 2.5 2.6 2.7 2.8 INSTALLATION Unpacking Location Power Requirements Antennas Speakers Headphone Operation Viewing Angle Options Rear Controls & Connectors 5 5 5 5 5 6 6 6 6 3. 3.1 3.2 3.3 11 OPERATION 11 Operating Controls Simplified Operating Procedurel2 12 Dia1 Calibration 4. 4.1 4.2 4.3 4.4 4.5 4.6 4.7 4.8 4.9 4.10 PRINCIPLES OF OPERATION Loop Amplifier R .F .
1. 1.1 GENERAL DESCRIPTION FEATURES The SPR-4 is an a11 solid-state communications receiver which can te programmed with accessory crystals to cover 150 kHz to 30 MHz. The SPR-4 receives AM, CW, SSB (Upper and lower ) and may be powered from 120 VAC, 240 VAC and 12 VDC. 1.2 SPECIFICATIONS 1.2.1 GENERAL SPECIFICATIONS Frequency Coverage : Can be programmed with accessory crystals for 23 ranges (each tuning a 500 kHz band ) from .5 to 30 MHz plus 150 to 500 kHz.
Audio Output Power: 3 watts into 4 ohm load (less into higher impedance loads ) . Hum and Noise: More than 60 dB below rated output. Calibration: Dial is accurate to better than _+ 1 kHz when calibrated to nearest 100 kHz calibration point. 1.2.2 POWER CONSUMPTION: 18 watts on 120 V DC, or 240 V AC, and 6 watts 2.5 watts on 12 V DC with dia1 lamps turned off. on 12VDC. 1.2.3 SIZE AND WEIGHT: 1.2.4 SEMICONDUCTOR COMPLIMENT: 5-1/2” H x l0-3/4” W x 12-1/4” D , 18 pounds .
Symbol CRl CR2 CR3 CR4 CRS CR6 CR7 CR8 CR9 CRl0 CRll CR12 CR13 CR14 CR15 CR16 CR17 CR18 CR19 CR20 CR21 Function Premixer Switch RF Amplifier Protection RF Amplifier Protection Zener Regulator Power Supply Rectifier Power Supply Rectifier Power Supply Rectifier Zener Regulator Zener Regulator AVC Switch AVC Switch Negative Supply Rectifier Negative Supply Rectifier Zener Regulator AVC Switch AVC Switch AVC Switch AVC Switch Product Detector Product Detector AM Detector Type lN270 lN4148 lN4148 lN714 B5G5
VIEWING ANGLE OPTIONS Figure 1.
2. 2.1 INSTALLATION UNPACKING Carefully remove the receiver from the shipping carton, and examine it for evidence of damage. If any damage is discovered, immediately notify the transportation company that delivered the receiver. Be sure to keep the shipping carton and packing material, as the transportation company will want to examine them if there is a damage claim.
50 to 100 feet long will give good results . An antenna kit (Mode1 AN-S) is available. For best single band performance, a half wave dipole or other resonant antenna , fed with unbalanced 50 ohm coaxial table, may be used . How- ever, Bands A and B require a long wire antenna. For directional reception on 150 kHz to 1600 kHz, the accessory AL-4 shielded loop antenna may be used. All antennas other than the AL-4 loop antenna, connect to the Ant. jack on the rear of the chassis. 2.
2.8.1 P O W E R The power connector mates with both the AC and DC power cords . See “2 . 3 ” 2.8.2 FUSE The fuse holder must have the proper fuse installed for 120 or 240 V AC operation . See “2 .3 ” 2.8.3 SPEAKER The interna1 speaker is normally connected to the speaker jack, when an external speaker is used, disconnect the interna1 speaker by removing the plug and connect the external speaker to this jack. 2.8.
The SPR-4 audio amplifier may be used with an external audio source such as a tuner. The level of the external source must be approximately .08 volts into a 3 K load . The received signals may be eliminated by turning the RF GAIN control counter-clockwise or by removing the mute plug l 2.8.9 DIAL LAMPS The DIAL LAMPS switch may be used to tum off the three dial lamps .
a,
3. OPERATION Refer to Figure 3 for the location of the operating controls. 3.1 OPERATING CONTROLS 1. The S-meter indicates the relative level of the received signals . 2. The crystal selector switch selects the band determining crystals . The top line of the dial sector reads the lowest frequency of each band in MHz, the middle line indicates the approximate position for tuning the preselector and the bottom line indicates the proper setting of the range switch. 3.
knob from the off position moves the rejection notch across the receiver pass band . 11. 3.2 The accessory switch turns on the S-NB Noise Blanker and the SCC-4 Crystal Calibrator if they are installed. The 5-NB and the SCC-4 are off in the NORM position. SIMPLIFIED OPERATING PROCEDURE As an example , suppose that the SPR-4 is to be tuned to 7272 kHz. First turn the crystal selector dial to the 7.0 MHz position. Set the preselector to 5.5 as indicated on the second line of the crystal selector dial .
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4. 4.1 PRINCIPLES OF OPERATION LOOP AM PLIFIER On Bands A and B , Q1 amplifies signals from the loop antenna and feeds one gate of the R.F. amplifier Q4, through C52 and the tuned circuits formed by C9, Cl0, C13, C16, C18, C22, C23, C25, C27, C33, T2, and T4. On Bands A and B, signals from an external antenna connected to J2 (AA) bypass Q1 through Cl0 and Cl3 into the tuned circuits described above. 4.2 R.F.
to one gate of the premixer, Q5 through C26 and R15. The P.T.O. drives the other gate of Q5 through R25 and C76. The P.T .O. is tuneable from 4955 kHz to 5455 kHz. The output of Q5 is tuned by the components associated with S4F, S4R, S8F, S8R and drives the 1st mixer through T6, S6R, C99 and C96. 4.5 SECOND MIXER The 2nd mixer, Q10, is driven by the 1st mixer and the crystal oscillator buffer Q17.
4.9 AVC SYSTEM The AVC threshold is established by the setting of R111, the R.F. gain control. R111 is normally operated fully clockwise . This applies approximately +2 volts to the AVC line through R104, R100 and CR15 with no received signal. Signals from T16 drive Q25 into base current on the positive R .F . driving cycle which pulls the collector negative because the emitter is returned to the - 5 volt line.
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5. 5.1 ALIGNMENT REMOVING COVERS Remove the AL-4 Loop Antenna if it is in use. Remove the top three screws on each side of the SPR-4 and remove the top cover by pulling up on the rear and then on the front of the cabinet. Remove the remaining screws from the bottom cover and lift the SPR-4 from out of the bottom cover. 5.2 TROUBLE SHOOTING Careful consideration has been given in the design of the SPR-4 to keeping maintenance problems to a m i n i m u m .
5.3.1 5.3.2 4. An accessory crystal for reception of WWV standard frequency transmission that is most reliably received in your area. See Page 33 to determine crystal frequency required. This crystal is not required if SPR-4 does not have an SCC-4 Crystal Calibra tor . 5. A 47 ohm 1/2 watt composition resistor connected across a phono plug to serve as an antenna load. 6. A scale with accurate 1/32 inch divisions. 7. An alignment tuning wand such as General Cernent GC 8273 or Walsco 25 16.
minal on the R.F. amplifier board at the left top corner, looking into the bottom of the SPR-4 and front pane1 facing you. This terminal has coax connected to it . Care should be taken not to short this point to ground because Q4 will be ruined, 2. Preset the balance pot on the 1st mixer board fully clockwise. 3. Set the signal generator to 5645 kHz and adjust its level for a slight AVC deflection. 4.
and mixer trimmers for maximum AVC deflection. Detune T6 by grasping a metal screwdriver shaft and touching it to the rotor contact of S4R, and tune the rear H band injection trimmer for maximum AVC deflection. Detune T1 by touching the rotor contact of S8F and tune the front H band injection trimmer for maximum AVC deflection. 6. Tune the G through C bands with the following set-up, tuning the R.F.
the notch control at 12 o’clock and adjust the main tuning knob for maximum AVC voltage ( positive going ) . Altemately adjust the notch control and the notch depth control, R57, for maximum AVC voltage (positive going ) . 5.3.5 S-METER ADJUSTMENT Tune in a 10,000 microvolt signal on 7.2 MHz LSB and looking into the top of the chassis with the front panel facing you, adjust R73, the left control on the S-meter circuit board for + 4.
6. ACCESSORIES 6.1 MCDEL SCC-4 CRYSTAL CALIBPATOR 6.1.1 GENERAL DESCRIPTION 6.1.2 6.1.3 The SCC-4 is a 100 kHz crystal controlled oscillator that injects into the receiver a harmonic every 100 kHz throughout the SPR-4 frequency coverage . INSTALLATION Remove the top row of 3 screws on each side of the SPR-4 cabinet. Disconnect the power cord, internal speaker cable and remove cabinet top. Install the SCC-4 by inserting it into the socket marked CALIBRATOR at the left rear of the SPR-4 chassis.
puls e. Between noise pulses , full receiver gain is restored . Receiver AVC is affected only by the desired signal and not by noise when the 5-NB is in use. The 5-NB is most effective on strong, periodic impulse noise such as ignition noise. 6.2.2 INSTALLATION T O install the 5-NB, remove the top row of three screws on each side of the SPR-4 Receiver cabinet. Disconnect the power cord, the internal speaker cable and remove the cabinet top.
reverse biased and turned “off”. With the series gate “off”, the signal path through the 5-NB is broken and reception is blanked for the duration of the interferring noise pulse. The 5-NB is turned on by the accessory switch in the SPR-4 which removes the ground from Pin 1 of P-5 and allows Q3 in the 5-NB to oscillate permitting signals to mix in the 5-NB balanced mixer and eventually operates the series gate. 6.2.
When the mode switch is in the AM or USB position, shorting the RTTY jack will have no effect. 6.3 .2 INSTALLATION This modification should be made by a competent technician. If you need help or want the RY-4 to be installed by one of our factory authorized service centers or by the factory service technicians , please call or write our Customer Service Department . Disconnect the speaker cable, the line cord , and remove the SPR-4 cabinet.
6.3.4 CIRCUIT DESCRIPTION The BF0 is shifted in frequency for RTTY reception by shunting a capacitor across T17 with an electronic switch . Transistor Q2 electronically switches C2 across T17, and Q3 switches C3. Switch S14R connects the collector of Q1 to the base of Q3 in CW and to the base of Q2 in LSB . If Jl (RTTY jack) is shorted, Q1 conducts and turns on either Q2 in LSB or Q3 in CW, allowing reception of RTTY signals . 6.3.
Late SPR-4’s have a 12 K 1/2 watt resistor between T-6 and the preCut the resistor lead from T-6 and remove the resistor. Route mixer board the coax cable along the wiring harness and install the phono fitting on the end of the cable in the large hole near the center of rear chassis apron a s shown in Figure 17 . The nut and the flat washer should be on the outside of the chassis . pins . . Remove the SPR-4 S-meter lamp bracket by squeezing the sides of the bracket.
6.4.4 CIRCUIT DESCRIPTION The transceive switch on the T-4/T-4B/T-4X/T-4XB Transmitter controls the TA-4 by applying a negative or positive D.C. potential to the injection c a b l e. When the transceive switch on the transmitter is in SPOT position, no D.C . potential is applied to the injection cable and the injection cable is not utilized . In SEPARATE position, the injection line is connected to the mute jack through a 68 K resistor.
CONTROL OR SWITCH S PR-4 Band or Range switch Crys tal switch Function Mode Audio Gain Transceive Anti -Vox S ideband D 3.5 --LSB 3 o’clock ------- Preselector Both the SPR-4 and T-4XB preselectors should be set to about 6.5 and peaked for the loudest “canary” sound from the speaker. T-4XB 3.5 --SSB --_ --spot Full clockwise Lower Adjust C-2 in the T-4XB until the “canary” sound slows down to only a few chirps a second and then zero chirp a second and a l l that is heard is a single tone. 6.
6.5.3 AVC OFF ALTERATION The AVC may be remotely turned off in SPR-4’s with serial numbers above 1,000. This is obtained by altering connections to two terminals on the power supply board . One of these two terminals has two white/bIue wires attached . Cut the jumper from these two terminals and connect an external SPST switch across these terminals for AVC OFF operation.
SPR-4 ACCESSORY CRYSTAL CHART OPERATING FREQ. in MHz. CRYSTAL FREQ . in MHz. OPERATING FREQ. in MHz. .15 .5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5 9.0 9.5 10.0 10.5 11.0 11.5 12 .o 12.5 13.0 13.5 14.0 14.5 None Required . 11.59 12.09 12.59 13.09 13.59 14.09 14.59 15.09 15.59 16.09 16.59 17.09 17.59 18.09 18.59 19.09 19.59 20.09 20.59 21.09 21.59 22.09 22.59 23.09 23.59 24.09 24.59 25.09 25.59 15.0 15.5 16.0 16.5 17.0 17.5 18.0 18.5 19.0 19.5 20.0 20.5 21.0 21.5 22.0 22.
SERVICE DATA FOR SPR-4 ACCESSORIES 6.6 SCC-4 D.C. and R.F. VOLTAGE CHART Transistor Drain Collectr Source Emitter Gate Base Q1 3 . 3 (3 v) 3.0 .8 Q2 6.2 (670 mV) 2.4 0.0 t MEASUREMENT CONDITIONS Conditions same as the SPR-4 R.F. VoItage char-t with the accessory switch in CAL position. 11 megohm VTVM and Boonton Mode1 9 1 CA R.F. voltmeter used . 100:l divider used on measurements above 500 mV. Measurements in parenthesis are R.F. voltages.
Note: All components on this board are not shown. -JUMPER TO THIS LEAD “SEE TEXT” ,‘^.. . -” ,! 0 RY-4 CALIBRATION CONNECTION TO SPR-4 Figure 8 + 3 220 0 c4 .Oi \l * _ CRI 1N270 SCC-4 SCHEMATIC DIAGRAM Figure 9 - 35 - ‘“‘“-L = 3 “” 2.
5-NB D . C . A N D R . F . V O L T A G E C H A R T Transistor Drain Collector Source Emitter Gate 1 Base Ql 12.1 (31) 2.6 8.5 (3.4V) 3.1 (9.4) 12.3 (57) 12.3 (57) 9 . 6 (12.5) 9.3 (290) 9.0 11.5 4 . 4 (650) 11.8 12.3 12.3 6.2 2.7 2.7 2.4 3.4 1.8 (6.4) 1.0 1.4 2.7 2.7 1.25 8.2 (21) 0.0 5.5 3.85 3.3 0.0 2.4 3.4 3.0 3.0 2.5 0.0 0.0 3.4 3.4 1.8 8.8 0.2 6.1 4.3 3. 8 0.0 3.4 Q2 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Q10 Q11 Q12 Q13 Q14 Q15 Q16 (4) (3.
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Base Transistor Collector Emitter Q1, CW Ql, LSB - 1.4 - 1.1 8.8 8.8 8.7 8.7 Q2,, CW Q2, LSB 29 30 2.2 2.2 -. 3 -. 3 Q3,, CW Q3, LSB 33 33 2.2 2.2 -. 5 -. 5 MEASUREMENT CONDITIONS Conditions same as the SPR-4 R.F. voltage chart . RY jack shorted to ground . 11 megohm VTVM used. RY-4 D .C.
S\4R Q1 - \tA R3 - TO EMITTER R4 l+A C3 .
INJECTION ANTI-VOX TA4 CIRCUIT BOARD INSTALLATION DIAGRAM Figure 16 PWR SUPPLY AND ~~~AGC TA-4 PICTORAL WIRING DIAGRAM F i g u r e 17 - 42 -
TA-4 D.C. Transistor Transceive Mode VOLTAGE CHART Collector Emitter Base Q1 Q1 Separate Transmitter --------- 0.0 0.0 0.7 0.7 Q2 Q2 Separate Transmitter 0.05 11.1 0.0 0.0 0.6 0.0 Q3 Q3 Separate Transmitter 12.2 0.02 12.2 11.9 11.5 10.6 Q4 Q4 Separate Trans mitter 0.0 0.02 0.0 0.0 0.6 0.6 Q5 Q5 Separate Transmitter 0.0 2.3 0.01 3.0 12.2 12.0 MEASUREMENT CONDITIONS Conditions same as the SPR-4 R .F . voltage chart and including inter-connection with a T4XB.
2Ni394TA-4 CIRCUIT BOARD Figure 18 - 44 -
r YELLOW TO CENTER TAP T-6 TA4 SCHEMATIC Figure 19 - 45 -
SPR-4 D.C. Transistor Drain Collector Q1 Q2 7.3 9.0 PT0 9.7 9.8 PT0 10.2 10.2 17.0 11.8 6.3 12.2 6.0 Q3 Q4 Q5 Q6 Q7 Q8 Q9 Ql0 Qll Ql2 Q13 Q14 Q15 Q16 Q17 Ql8 Ql9 Q20 Q21 Q22 Q23 Q24 Q25 Q26 Q27 Q28 6.0 12.2 0.5 10.0 1.7 7.0 5.4 5.5 8.8 11.2 11.6 1.6 4.6 8.6 4.8* VOLTAGE CHART Source Emitter .l 4.3 ----.3 .8 ----3.0 2.8 12.7 .25 1.8 6.0 0.0 4.0 6.5 6.0 3.9 11.0 5.4 0.0 0.3 0.15 0.15 0.3 -4.7 4.6 2.5 0.2* Gate 1 Base Gate 2 .8 3.9 ----1.3 0.0 ----0.0 0.0 13.2 0.0 0.0 6.5 0.5 0.4 7.0 5.4 2.
SPR-4 R.F. VOLTAGE CHART Trans is tor Function Drain Collector Gate 1 Gate i Source Q1 Loop Amp RF Amp 1st Mixer 2nd Mixer 1st IF Amp 2nd IF Amp Range Xtal Osc. Premixer Xtal Osc. Xtal Osc. Buffer Neg . Supply Driver BF0 131” 16 215** 900** 310 1V 4V 2.5V 3V Q4 Q7, Q8 Q10 Q23 Q24 Q5 Q11 Q17 Q21 Q27 T 2.15V 480 2.8V 4.25V 1.35V All voltages are millivolts RMS except those marked V (volts) MEASUREMENT CONDITIONS Set signal generator to 7.0 MHz and 1 millivolt at the SPR-4 antenna jack.
2N 3394 MFE 3007 *SFC4982 @ tg *2N 5949 *2N 5950 TIS88 *2N 5245 *2N 5246 2N 4125 2N 3566 9 * SERIAL N O ' S ABOVE 1000 TRANSISTOR LEAD CONFIGURATION F i g u r e 21 - 49 - 8 5030 CA 3053
TERMINAL(PC SIDE) LOOP ANTENNA CIRCUIT BOARD Figure 22 - 50 -
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R57 20K POT
Cl41 c?.
RW
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