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R. L. Drake Company, Miamisburg, OH

SPR - 4

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überarbeitet am 19.10.2010

Between the appearence of Drakes R-4B and R-4C receivers, Drake brought out a completely solid state shortwave receiver in 1969: their SPR-4 was constructed for the needs of shortwave broadcast station listeners.
The set looks similar to the R-4 series receivers, but it can recognized easily from the third dial window in the frontplate: between the signal strength and the frequency readout windows, You find the shortwave band segment displayed, together with recommendations for the BAND RANGE and PRESELECTOR tuning settings. Continuous coverage through the complete shortwave spectrum is only available with the external frequency synthesizer FS-4 connected.

Double conversion, 1st IF 5,645 MHz, 2nd IF 50 kHz

Linear analog dial 1 kHz

Long- and mediumwaves and 7 shortwave broadcast bands, 14 additional 500 kHz segments optional,
continuous coverage with FS-4 frequency synthesizer

AM, USB/LSB, CW

Sensitivity 5 MHz
AM < 0,5 uV, SSB < 0,25 uV

Selectivity -6/-60 dB
SSB 2,4/7,2 kHz, AM 4,8/10 kHz, CW 0,4/2,7 kHz

RF-Gain, Notch, (Noise Blanker optional)

The metal cabinet has the same dimensions as found in other R-4 series sets, it's dimensions are 274 x 140 x 324 mm ant it's weight 7,75 kg.
The completely solid state set can be powered from 120 or 240 V mains or with a car adaptor cable from 12 DC, the power consumption is 6 Watts, when dial lights are switched off, only 2,5 Watts.
So this is the only one in Drake's R-4 receiver series that's really useable for mobile operation.

The SPR-4 has an integrated speaker, it can also be attached to Drake's MS-4 matching external speaker. Drake offered a Noise Blanker circuit NB-5, a crystal calibrator SCC-4 (both to be plugged into a socket on the chassis), a long- and mediumwave Loop Antenna AL-4 that can be plugged in to a socket at the top of the cabinet, and a RTTY adaptor, that will shift Your BFO to correctly receive the 2125 and 2295 Hz tones. With the TA-4 Transceiver Adaptor, the SPR-4 can be used together with a T-4 or TX-4 transmitter in transceive operation.

In the light grey top section of the SPR-4's front panel, You find the signal strength meter calibrated in S units, the band segment switch and the main tuning dial, all backlit in Drakes' typical bright blue colour.
The band selector is the small knob underneath the middle window, a yellowish illuminated sector will indicate the start frequency of the selected 500 kHz band segment, a number indicates the recommended position of the preselector and a letter the respective BAND RANGE switch setting.
The main tuning knob is situated below the frequency dial indicating the reception frequency with an accuracy of better then 1 kHz, the dial consists of two concentric transparent discs with the 0 - 90 and 0 - 900 marks printed on them.
In the row of knobs below the preselector control, You will find the band RANGE switch with it's letters leftmost, the headphones jack and then two concentric knobs for RF gain and AF gain (volume), this switch will also act as mains switch.
The reception mode switch has positions for AM reception, for narrow CW reception and for LSB and USB reception. An additional knob at the right hand below the main tuning knob sets the receiver in normal receiving mode, activates the Crystal calibrator and the Noise Blanker mode, the center of the concentric knobs controls the passband of the famous Drake RF Notch filter to eliminate interference from adjacent channels.

From the antenna jack or the connector of the Loop antenna, the RF signal is directed to a preamplifier, a first RF amplifier stage and will me mixed to a first intermediate frequency of 5645 kHz in the first mixer stage. After mixing to the second low IF of 50 kHz, the signal has to pass through the Notch circuit and the bank of coil IF filters. Due to the low intermediate frequency, these coil filters offer a good skirt selectivity for a reasonable price. After beeing amplified, the signal will reach the AM (diode) detector or the product detector stage for SSb reception, the signal of the Beat Frequency Oscillator will be injected here.
The necessary oscillator signal are generated by a quartz oscillator, a different crystal has to be switched in the circuit for each of the 500 kHc segments, in combination with a permeability tuned highly linear VFO oscillating in the 4905 - 5505 kHz range.

The operation of the SPR-4 is typical for earlier Drake sets and not completely straightforward. You switch the set on using the AF gain / volume ccontrol. Set the MODE switch to AM reception. Now turn the Band Segment switch to select the appropriate 500 kHz segment, e.g. the 6 MHz segment for the reception of Vienna's External Service on 6155 kHz. The number and the letter appearing in the window will indicate the recommended settings for the BAND RANGE switch (in this example the E) and the preselector setting, to continue with this example the 4 will be the right choice.
To tune in to 6 1 5 5 kHz, set the main dial to 155 and You might already hear something. Tweak the preselector control for maximum S meter reading and readability. After switching to LSB or USB, You may retune with the main tuning knob to zero beat (this will mean until the hiss disappears and the voices sound natural and not like Mickey Mouse anymore) und select the upper or lower sideband for single sideband (ECSS) reception.

Overall, the SPR-4 is completely solid state communications receiver well suited for broadcast station DXing and for picking up amateur radio traffic. You will find a good dynamic range and rejection of unwanted signals, but You will have to accept to select Band Range and adjust the preselector manually after changing frequencies every time. With these disadvantages and the selective coverage of only a selected choice of bands, the SPR-4 is regarded as a collector's item more then a contemporary DXing machine. You can improve the set's performance for general coverage by connecting to a FS-4 frequency synthesizer offering You a choice of all 500 kHz segments up to 30 MHz.

weitere Lektüre:
d/e: Drake SPR-4 at www.radiomuseum.org
d: Drake SPR - 4, J.Biesinger, kurier 2/94
d: Empfindlicher Star auf allen Bändern: Drake SPR-4, Nils Schiffhauer, Oldie-KW-Empfänger
d: Drake SPR - 4, R. Lichte, Kurzwellenempfänger - Qual der Wahl

© Martin Boesch 26.9.1999