R. L. Drake Company, Miamisburg, OH
SPR - 4
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 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 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.
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 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.
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.
© Martin Boesch 26.9.1999