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EKD 500

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überarbeitet am 22.10.2010

In the late seventies, RFT brought out their EKD 100, a communications receiver with decadic knobs tuning and in 1980/81 their EKD 300 with digital frequency display and a conventional tuning knob as well as direct frequency entry by means of a keypad. These receivers found common use in military and official services in East Germany and other eastern European countries and they have been replaced by the EKD 500, a receiver which added memories and scanning functions, in 1986. Thia radio can be remotely controlled or can control another receiver in the master - slave mode.
It's successor, the EKD 700, saw only a small protoype / early production run before RFT Koepenick closed down as a sequel to the merger of both German states.

EKD 511 Basic receiver EKD 501, 14 kHz - 30 MHz; Filter 1st I.F. -3 dB +/- 5 kHz, SSB I.F. filter +/- 0,25 - 3 kHz
EKD 512 Basic receiver EKD 502, 14 kHz - 30 MHz; Filter 1st I.F. -3 dB +/- 8 kHz; SSB I.F. filter +/- 0,25 - 6 kHz
EKD 514 Basic receiver, 10 kHz - 30 MHz; Filter 1st I.F. -3 dB +/- 5 kHz; SSB I.F. filter +/- 0,25 - 3 kHz
EKD 515 Basic receiver, 10kHz - 30 MHz; Filter 1st I.F. -3 dB +/- 8 kHz; SSB I.F. filter +/- 0,25 - 6 kHz

 

Double conversion, I.F. 70,2 MHz, 200 kHz

Digital display , accuracy 10 Hz

AM, USB, LSB, CW, FAX, ISB

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

Selectivity -6 dB
150 Hz, 400 Hz, 750Hz, 1,75 kHz, 3,1 kHz, 6 kHz,
+/- 0,25 - 6 kHz SSB

RF gain, 99 memories, scanning modes, computer remote control optional, master / slave operation as standard

The EKD - 500 comes with a rugged metal cabinet with the dimensions 54 x 19,8 (feet included) x 39,5 cm, the chassis can be pulled out of the cabinet after the four screws marked with a red coloured ring are unscrewed. The receiver has a weight of 25 kg. It can be powered by 127 or 220 Volts mains or from a vehicle battery or emergency battery in case of mains failure.

In the left upper corner, next to the protective / carrying handles, You find the grill of the small monitor speaker and below two multipole connectors to feed the audio signal to headphones or a tape recorder. A rotary control just below the monitor speaker selects the audio signal, in ISB mode (independent sideband), You can feed both sideband audio channels (channel A, USB / channel B, LSB) to the monitor speaker or in external speaker, for normal operation with the monitor speaker, the switch should be set to position 4. Just below, You find the volume / A.F. gain control and at it's right the R.F. gain control. The rotary knob marked A1 is the BFO note control.

The ten digit yellow - green LED display is the main information display of the receiver - the EKD 500 has only very few analog rotary controls to adjust volume and R.F. gain.
A flashing LED EXT indicates that the EKD 500 is in slave mode waiting for external operation commands, it is constantly on when the radio is remotely controlled.
he first two digits of the LED display gives the information about the acive receiving mode and the chosen I.F. bandwidth. A small table explains all different number codes. So "26" stands for AM reception with the 6 kHz I.F. filter and "43" for SSB reception (USB) with the 3 kHz i.f. filter. The letter "E" in the next segment indicates standard reception mode, the following seven digits indicate the reception frequency with a display resolution of 10 Hertz.
With the numbered keypad and the keys below the frequency display, You can directly enter an operation frequency, select the recepetion mode and the i.f. filter bandwidth and store and recall frequencies from the receiver's memory.
For direct frequency entry, for example to tune the set to the European standard frequency of Radio Austria, Vienna, on 6155 kHz, You have to press the buttons F (frequency entry) 6 1 5 5 . 0 0 or F 6 1 5 5 E (E = Empfang / reception) or F 6 1 5 5 >. To select the tuning steps, use the buttons dF (delta frequency) 0 . 5 0 to set the tuning steps to 500 Hz.
To selecto the reception mode, press the button MOD and the corresponding key You have looked up in the modes table, e.g. for AM mode (A3) use the key sequence MOD 2. Use the B button (stands for bandwidth) in the same way to select one of the i.f. bandwidths. The key GC (gain control) ist used to select fast and slow AGC control, manual r.f. gain control or the combined control, the combination SEL O turns off the electronic tracking preselector, with SEL 1, the electronic preselection is active so that only a small portion of the complete antenna signal is fed to the first mixer.
You can store up to 99 frequencies / reception modes / fiolter settings to the 99 memory channels of the EKD 500. The keystrokes STO 5 E or STO 5 > will store the active frequency and receiver settings into memory channel 5, with CALL 5 >, the content is recalled from the memory the the receiver's frequency display and with the key E (Empfang = reception), the EKD 500 is switched to the frequency indicated on the display, so You can check the memory's content before tunign the receiver to the new memory channel. With the keys CALL98 and CALL99, You can set the receiver to a priority channel and the maritime emergency frequency. SCAN activates different scanning modes, the start frequency has to be stored on memory channel 96 and the end frequency on memory channel 97. EXT activates the slave mode when the EKD 500 is to be remotely controlled from another EKD 500 receiver, when You press the keys EXT and EXT-FKT at the same time, the receiver will be switched backto normal operation.

You can not only use the frequency keypad to enter a reception frequency, You can also use the conventional tuning knob. The tuning steps can be programmed as I have written in the description above, the main tuning knob itself is quite a small plastic knob.
Just above the tuning knob, You find a rotary control to select the function of the row of LEDs. It can be set to act as a signal strength meter (one LED step stands for 10 dB), as A.F. level indicator and as tuning aid for radioteletype reception. Another LED indicates the lock of the carrier synchronisation when in automatic ECSS mode.

The EKD 500 as a professional communications receiver is intended for remote control. It can be controlled as a slave receiver from another EKD 500 or from a personal computer over a modem an telephone line. Via remote control, the memory content can be altered and memory contents can be copied from one receiver to another, You find a description of all these possibilities in the user's manual.
The receiver features an automated self test, press the EXT and EXT-FCT keys for a self test, the receiver will display AA and after You release the keys AO to indicate everything is fine, in case You get errors, You can do further tests to locate the error.

The R.F. signal first has to pass a protective bulb (it will blast with voltages higher then 30 V EMK to protect the receiver's front end), after that, it will pass an array of electronically switched suboctave band filters. These can be inactivated when the receiver is in scanning mode. After having been mixed with the oscillator signal of 70,21400 - 100,19999 MHz (the receiver is tuned in 10 Hz increments), the first intermediate frequency of 70,2 MHz is generated. After an amplifier stage, the i.f. will have to pass a monolithic +/- 3 or 5 kHz crystal filter. After having been mixed to the second I.F. of 200 kHz, the signal has to bass the high quality mechanical I.F. filters. For AM, diode demodulation and for single sideband reception, a product demodulator is used. The EKD 500 gives You the option of automatic ECSS reception: the receivers internally generated carrier is synchronised with a poor carrier rest of the station's signal and locks automatically on the correct frequency. The EKD 500 is also fully ISB capable, this will say, it can receive transmissions with two different sideband informations on the upper and lower sideband and will feed the audio channels A and B to the audio sockes or the monitor speaker. The receiver also has demodulators for F1 / radioteletype modes.

In practical use, the EKD 500 is very convincing with it's very high sensitivity, excellent dynamic range due to the electronic preselection with suboctave filters and high stability. The sound from the internal monitor speaker is not perfect, so an external speaker, maybe in combination with an audio equalizer or an external A.F. notch filter might do a good job.
The operation scheme with the different number / letter combinations for the reception modes is a bit complicated. After You have learned to standard combinations, the receiver is extremely flexible and quick to work on.
The performance on the shortwave bands is excellent, for standard AM operation and even more in single sideband reception and exotic reception modes such as ISB and radioteletype operations. The small tuning steps and the high stability oscillators do a very good job.
The most impressive moments with my EKD 500 was the annual special transmission from Radio St. Helena: on my NRD-535, I could only identify some speech or music fragments, with the EKD 500, I could understand every word of the station identification and could even understand the content of the telephone calls transmitted over the airwaves.

weitere Lektüre:
d: Kurzwellenempfänger EKD 500 - eine preiswerte Alternative in der Spitzenklasse, Ch. Tholen, G. Wetzger, Radio hören 4/96

© Martin Bösch