| The Drake model
SPR-4 communications receiver may be programmed to suit your present and
future needs. It is ideal for short wave listening or monitoring, aircraft
radio and weather, marine ship and shore stations, hf communications, WWV
time signals, CB, standard broadcast monitoring or DXing, amateur radio,
civil defense, government, or use as a laboratory instrument.
In designing the SPR-4, Drake engineers
incorporated the dual gate FET to produce the first no-compromise solid
state receiver. Unlike receivers with bipolar transistors which have poor
cross-modulation, inter modulation, agc, and overload performance; the
SPR-4 has signal handling capabilities superior to the best tube
receivers. In addition, the SPR-4 has all communications receiver of the
advantages of a solid-state design such as low power consumption,
mechanical and thermal stability, reliability, etc.
The SPR-4 comes with ten bands installed
which cover long wave, standard broadcast, and seven shortwave broadcast
bands. Other bands, each with 500 kHz tuning range, can be added by
purchasing a crystal which comes with an adhesive transparent dial sector
for that range. A total of 24 bands are possible from 150 kHz to 30 MHz.
The main tuning dial reads 0 to 500 kHz
with 1 kHz graduation marks using two concentric transparent discs, 0 to
100 kHz is indicated on one disc and hundreds of kHz are indicated on the
other disc.
SPECIFICATIONS
 | Frequency Coverage : Can be programmed
with accessory crystals for 23 ranges (each tuning a 500 kHz band)
from 0.5 to 30 MHz plus 150 to 500 kHz. |
| Crystals supplied with the receiver :
allow coverage on these ranges: 150-500 kHz, 0.5-1.0 MHz, 1.0-1 MHz*,
6.0-6.5 MHz, 7.0-7.5 MHz, 9.5-10 MHz, 11.5-12 MHz-, 15-15.5 MHz,
17.5-18 MHz, 21.5-22 MHz. |
| Modes of Operation : AM, CW, Isb, usb, (RTTY
with RY-4 accessory installed) |
| Selectivity:
A-m: 4.8 kHz @ -6 dB, 10 kHz @ -60 dB
Ssb: 2.4 kHz @ -6 dB, 7.2 kHz @ -60 dB
CW: 0.4 kHz @ -6 dB, 2.7 kHz @ -60 dB |
| Intermediate. Frequencies : 1st I.F.
5645 kHz four pole crystal lattice filter, 2nd I.F. 50 kHz four pole
Hi-Q Ferrite LC filter |
| Frequency Stability : At room
temperature, drift for all causes (including +- 10% change in supply
voltage) is less than +- 100 Hz. |
| Sensitivity : |
| Image Rejection : |
| Blocking : An undesired unmodulated
signal at least 20 kHz above or below a desired signal of .25
microvolt must be 90 dB stronger than the .25 microvolt signal to
cause a 3 dB reduction of the signal to noise ratio of the desired
signal. An unwanted signal (modulated 30% at 1 kHz) removed by at
least 20 kHz from a desired signal of 1 microvolt, must have a signal
level of at least 10 millivolts to produce a noticeable cross
modulation of the desired signal. |
| Cross Modulation : Using a reference
signal of .25 microvolt, two interfering signals of equal strength
within the passband of the receiver front-end selectivity must each
have a strength of at least 65 dB above the reference signal to
produce third order products equal to the .25 microvolt reference
signal. |
| Automatic Gain Control : |
| Input Impedance : |
| Excessive Rf Input : |
| Voltage Protection : continuously. |
| Output Power : |
| Power Consumption : |
| Calibration : |
| Hum and Noise : More than 60 dB below
rated output. |
| Size and Weight : 5.5"H x
10.8"W x 12.3"D (14 x 27.4 x 32.4 cm) 18 Ibs (8.2 kg) |
ACCESSORIES
| Matching Speaker : MS-4
Speaker |
| Calibrator : SCC-4
Crystal Calibrator |
| Noise Blanker : Plug-in
i-f type noise blanker mutes receiver for duration of each noise
pulse. 16 transistors, 2 diodes. Model
5-NB |
|
Line amplifier:
Installation of a LA-4 will
result in a output of 1 mW nominal into a 600 ohm balanced line. |
| Loop Antenna : Directional
antenna nulls out undesired stations, plugs into receptacle through
top of the cabinet, operates from 150 kHz to 1600 kHz only. Model
AL-4 |
| Antenna Kit : Consists
of wire, insulators, lead-in, and instructions. Model
AN-5 |
| DC Power Cord : Plugs
into cigar lighter in an automobile, allows SPR-4 to be used on 12
volts dc supply. Model DC-PC |
| Teletype Adapter : RY-4 |
| Transceiver Adapter : Allows
SPR-4 to transceiver with all T-4 and T-4X Transmitters. Consists of
printed circuit board and connectors. Model TA-4 |
SPR-4 CRYSTAL KITS
| Amateur
Bands : 160
M, 80 M, 20 M, 15 M, and 10 M ranges. Six crystals cover 1.5-2, 3.5-4,
14-14.5, 21-21.5 ,28-28.5 ,28.5-29 MHz. |
| Marine
Bands : 2-2.5,
2.5-3 ,4-4.5, 8-8.5 ,8.5-9 , 12-12.5, 13-13.5, 16.5-17, 17-17.5,
22-22.5, 22.5-23 Eleven Crystals |
| CB
: 27-27.5 MHz One
Crystal |
| MARS
: 2.0-2.5, 3-3.5, 4-4.5,
5-5.5,18-18.5. Five Crystals |
| Teletype
Commercial : UPI,
AP Stock Market, Weather, etc. 7.5-8, 9-9.5, 13.5-14, 15.5-16.Four
Crystals |
| Individual
Bands : Crystals
may be ordered for any 500 kHz tuning range. Specify Range in MHz. |
SPR-4 PRINCIPLES
OF OPERATION
Click to enlarge
|
LOOP AMPLIFIER
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 C10 and C13 into the tuned
circuits described above. |
|
R.F. AMPLIFIER
On Bands C through H signals from an external antenna connected to J2
(ANT ) are coupled to Q4 through T3 and C52..T3 is resonated with C101
and the capacitors connected to S5R. Q4 is protected from large
signals by CR2 and CR3 which are reverse biased. CR2 and CR3 limit the
signal to a safe level by conducting when a large signal overcomes
their reverse bias .
On Bands A and B the drain of Q4 is untuned and drives the 1st mixer
through C90 and C96. On Bands C through H , the drain of Q4 is tuned
by T5, the capacitors connected to S9F, and drives the 1st mixer
through C90. |
|
FIRST MIXER
The 1st mixer is a balanced mixer comprised of Q7 and Q8 and driven by
the R .F. amplifier and the pre-mixer . On Band A, the pre-mixer is
by-passed and the 1st mixer is driven from the P.T.O. through R25 and
C99. On Bands B through H, the pre-mixer drives the 1st mixer through
T6 and C99. The 1st mixer is balanced by R40 and the output is tuned
by Cl02 and T8 and drives the 2nd mixer through C110, the 5645 crystal
filter, and T9. Heterodyning of the R.F. amplifier and pre-mixer (P.T.O.
on Band A) results in a difference frequency output from Q7/Q8 of 5645
KHz. |
|
PREMIXER
The premixer system consists of the P .T .O. , the crystal oscillator
Q2, the premixer transistor QS, and the tuned circuits associated with
S1, S4F, S4R, S8F, and S8R.
The collector of the crystal oscillator Q2 is tuned by L5 and the
components connected to S1. The feedback winding on L5 is connected
through S2 to the proper range ctystal and the output of Q2 is
connected 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. |
|
SECOND MIXER
The 2nd mixer, Q10, is driven by the 1st mixer and the crystal
oscillator buffer Q17. Q10 is coupled to the 1st IF amplifier through
the The notch filter and the 50 kHz four pole Hi-Q ferrite L C filter.
Heterodyning of the 1st mixer and crystal oscillator results in a
difference frequency output from Q10 of 50 kHz. |
|
I.F. SYSTEM
The I .F . system is composed of the 1st I .F . amplifier, Q23, which
drives through T15, the 2nd I. F. amplifier, Q24. C169 and C187 tune
T15 and T16 respectively to 50 kHz and T16 drives the detection
systems . |
|
DETECTION SYSTEMS
 |
AM DETECTION
The AM signal from T16 is detected by CR21 and amplified by Q28 to
a level matching the output level of the product detector and is
applied to the audio gain control through C167 and S14F. |
|
CW AND SSB
DETECTION
CW and SSB signals from T16 are detected by the product detector
made up of CR19, CR20, R122, R123, and Q27, the beat frequency
oscillator. The output of the product detector is applied to the
audio gain control through S14F. |
|
|
AUDIO AM PLIFIER
A portion of the audio signal, determined by the setting of R101, is
applied to Q22 through a low-pass filter consisting of L10, L11, C164,
R97, R95, C163, and C159 which eliminates any residual 50 kHz signal
from driving the audio amplifier. Q22 amplifies this audio signal and
drives Q20 through C 148 where further amplification occurs and Q20
drives Ql6 directly and Q15 via Q19 which is unity gain common base
amplifier. Q12, Q15 and Q13, Q16 are darlington connected amplifiers
and the configuration of Q16 establishes a phase inversion permitting
Q12 and Q13 to operate in push-pull, Q12 and Q13 operate the speaker
or a headphone through coupling capacitor C127. |
|
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. The negative
potential on the collector of Q25 is applied to the AVC line through
CR18 and to C171 through CR17. The rate that C162 is charged
determines the AVC attack time. The AVC release time is determined by
the rate that C 171 discharges through R100 allowing Cl62 to discharge
through CR15. The attack and release times for Q4 are lengthened by
R22 and C70 to eliminate undesirable transients. Large signals are
kept from overloading Q4 by the application of a positive voltage on
Pin 3, the signal gate. This voltage is derived from the S-meter and
Q-18 and the delaying circuit of CR10, R47, R52, and C180.
On AM , S14R shorts out CR10 to obtain a symmetrical attack and
release response. |
|
MUTING
Muting is accomplished by placing an open circuit at J9 which removes
base current from Q26, lowering its collector voltage to -5 volts. The
cathode of CR16 will also be at -5 volts causing it to conduct,
applying cut-off voltage on the AVC line which turns off Q4, Q10, Q23,
and Q24 and mutes the receiver. |
|
S -METER
The S-meter is a voltmeter that measures the AVC voltage and is
calibrated in "S" units . The source follower Q14, is
connected to the AVC line and drives IC- 1 which is a differential
amplifier that operates the S-meter. The zero adjustment is affected
by R64 and the S-meter full scale sensitivity is set by R73. |
 Drake
SPR-4 Receiver (Recent
Equipment)
(c) QST 12/1970 - page 60 - 462 Kb file - Adobe
pdf version
SPR-4
Technical manual ( 66 pages- 15 002 Kb .pdf file )
|
