überarbeitet am 22.7.2010
In the middle of the fifties, the traditional electronics manufacturer Rohde & Schwarz from Munich presented a very heavy weight premium quality shortwave communications receiver, the EK 07. It's precision and production quality and also it's reception performance equalled or even surpassed the quality found in premium class U.S. receivers such as sets from Collins and Hammarlund. This receiver could be used in connection with an external FSK / SSB demodulator, a mechanic remote control and a panoramic registering unit.
It's successor, the EK 047 from the year 1969 featured a digital frequency display using nixie tubes and ISB (independant sideband) capabilities, further well known shortwave receivers were the EK 070 ten years later, the EK 085 in the year 1987 and the EK 890 / 891 which appeared in 1991, the latest top of the range receiver was the EK 896 from 1994 featuring personal computer control and DSP (digital signal processing) technology.
Double conversion superhet
, 1st I.F. 3,3 MHz, 2nd I.F. 300 kHz
Analog dial, linear, accuracy ca. 1 kHz, coverage 500 kHz - 30,1 MHz
Selektivity -6 dB
12 / 6 / 3 / 1 / 0.2 kHz
resp. for the EK 07 D
12 / 6 / 3 / 1.5 / 0.6 / 0.3 kHz
RF gain, three speed AGC, noise limiter, signal strength / audio level meter,
tubes voltage check, crystal calibrator
With it's dimensions of 54 x 33 x 55 cm (frontpanel width is a bit more then the standard 19 inch rack) and it's weight of 66,3 kg, the Rohde & Schwarz EK 07 is not only another huge receiver, it's bigger and heavier then the Collins R-390 or the Siemens E-311, only Telefunken's E-104 is quite a bit bulkier and heavier... But it's good to have two handles on each side of the cabinet, to get it lifted up on my shelves, I needed the help of my oldest son, my wife considered the thing as a bit to heavy...
The receiver can be powered from different mains voltages from 110 - 235 V and has a power consumption of 130 Watts to keep all 27 tubes glowing.
The frontpanel with the two protection handles is dominated by the very impressive 34 cm wide dial window between the two large format instruments, below the mainfrequency dial with a turret arrangement, You find the small window for the kHz indicator dial and below all other controls, the huge main tuning knob and the band selector switch activating theturret tuner arrangement.
The band selector switches the separate shortwave bands, each of them in most cases three MHz wide, in the dial window, the respective part of the shortwave dial drum will be visible.
Range I covers the lower half of the mediumwave band from 0,5 - 1,1 MHz, in the ranges II and III covering 1,1 - 2,1 resp. 2,1 - 3,1 MHz, the dial window is one MHz wide. In the higher frequencies ind the ranges IV to XII, each band is three MHz wide, the receiver's coverage is up to 30,15 MHz. In all these ranges, the main dial is only used for coarse tuning between two 0,1 MHz marks, You can read the kHz digits on a mechanically coupled dial in a small window just below the main frequency dial. The receiver is tuned with main tuning knob, it's outer ring has a 30:1 gear for fine tuning, the complete tuning mechanism can be blocked mechanically.
The left measuring instrument will display the A.F. level in position "600 Ohm" and the speaker output in position "16 Ohm". All other switch positiond "Überwachung" are used to control several voltages of the reciver, on all 27 positions, the pointer should remain in the red area indicating proper operation of the receiver. The right instrument will display the R.F. level in uV. Just next to the signal strength meter, You find a small pushbutton whick can be turned 90 dregrees when depressed to lock, it will activate the 300 kHz crystal calibrator.
All other controls are located in two rows oh nearly indentical knobs in the left lower segment of the front panel.
In the left lower corner, You find the main switch, one position will keep the valves heated for standby, in a third position, the receiver is on with dimmed dial illumination. Just above it, You find the volume control. At the next position at the right hand, You find the bandwidth selector with it's five (or with the EK 07/D variant six positions) and the BFO control for CW reception just above.The third knob in the bottom row activates the noise limiter and controls it's intensity. The knob above selects the AGC time constant from 0,1 / 1 and 10 sec. The fourth knob in the bottom row is the switch for automatic manual and nixed automatic - manual R.F. gain control and the R.F. gain control itself, just above it.
At the right and left side of the controls, You find the headphones jacks, a long row of additional connectors for antennas, the main oscillator and the 300 kHz crystal calirator oscillator output are located at the rear of the receiver.
The R.F. signal coming from the antenna will first have to pass an automatic preselection stage with twelve passbands and after an amplifier stage a synchroneously tunes band pass. After this, it will be mixed to a first intermediate frequency of 3,3 MHz in the ranges V - XII and then to the second i.f. of 300 kHz, below 6 MHz, the signal is directly mixed to 300 kHz as first intermediate frequency. After having passed several amplifier stages and the i.f. filters for the six bandwidths, the signal is fed to the demodulator stage after the AGC control voltage has been generated.
A diode demodulator is active for AM demodulation, for single sideband and CW operation, a BFO can be activated. For perfect single sideband reception, there has been an optional single sideband demodulator, the NZ 10. An optional demodulator for radioteletype operation could be used to directly drive a mechanical teletypewriter. There existed a mechanical remote control machine to control the EK 07 over telephone lines, control pulses did activate small motors which moved the frontpanel controls.
In practical use, the Rohde & Schwarz EK 07 is a strong competitor to other high end shortwave receivers from the sixties, it has a similar performance as the Collins R-390A, at least as fas as Am and CW reseption is concerned. Like with the Collins R-390, You need the optional single sideband demodulator for perfect single sideband demodulation, otherwise SSB performance is only fair when done with the internal BFO. But one has to remember, in most other receivers from that era, a BFO for SSB reception was all, the set did offer - Rohde & Schwarz did offer more, for another sum of money. So You could get, what money could buy in those years.
The receiver is quite resistant to overload and free of unwanted signals thanks to the automatic preselection; it has a very high stability and a very good dial accuracy with a dial resolution of better then 1 kHz.
Like with other commercial receivers from the fifties and sixties, the receiver is not equipped with the features to reject interfering signals such as a passband tuning or notch filter. Of course, the receiver has no frequency memories, so for an easy comparison of the reception quality on two frequencies, You have to quickly turn the main tuning control several times or You have to afford several EK 07, some commercial communications agencies did it this way...
Even today, the Rohde & Schwarz EK 07 is am exceptional performer an AM and CW and well suited for broadcast DXing, for SSB, You should look around for one of the very rare single sideband demodulators.
d: Die deutsche Antwort auf Collins ? Rohde & Schwarz EK 07, Nils Schiffhauer,
Oldie- KW- Empfänger
© Martin Bösch