Manufactured by RFT / VEB Funkwerk Köpenick, VEB Kombinat Nachrichtenelektronik, Köpenick.

At the end of the 1970s, the EKD100, an excellent double conversion receiver with frequency setting via decadic switches, and in 1980/81, the EKD300 with a digital frequency display, a numeric keypad for direct frequency input and a conventional tuning knob, were launched and made their appearence in the monitoring sites of East German military agencies. In 1986, this receiver was replaced by the EKD 500, which also had memory and scan functions and could be remote-controlled in master-slave mode. These last professional communication receivers built before German unification have excellent reception performance and are available on the second-hand market. Unfortunately, the successor - the EKD700 - hardly made it beyond the prototype stage. Besides two prototypes, only a small batch of 10 sets was built. Due to „liquidation“ of the RFT production plant after it was taken over by the Munich company Rohde & Schwarz, the EKD 700 never went into production.

EKD511: Basic unit EKD501, 14 kHz - 30 MHz; filter 1.IF -3 dB ±5 kHz, SSB IF filter ±0.25 - 3 kHz
EKD512: Basic EKD502, 14 kHz - 30 MHz; filter 1.IF -3 dB ±8 kHz; SSB- IF filter ± 0.25 - 6 kHz
EKD514: Basic unit, 10 kHz - 30 MHz; filter 1.IF -3 dB ±5 kHz; SSB- IF-filter ± 0,25 - 3 kHz
EKD515: Basic unit, 10 kHz - 30 MHz; filter 1.IF -3 dB ±8 kHz; SSB- IF-filter ± 0,25 - 6 kHz

• Principle: Double conversion superhet, IF 70.2 MHz, 200 kHz
• Operation modes: A1 with BFO, USB/LSB, AM (A3), ISB, F1
• Frequency range: 10 kHz - 30 MHz
• Frequency display: digital display, 10 Hz
• Frequency memory: 99 memory channels
• Signal strength indicator: LED bar graph display
• Signal processing: RF gain
• Features: Scan operation, computer control, Master / slave operation.
• Sensitivity: SSB < 0.5 μV / Selectivity: 150 Hz, 400 Hz, 750Hz, 1.75 kHz, 3.1 kHz, 6 kHz, +/- 0.25 - 6 kHz SSB (-6 dB)

• Mains operation: 127, 220 V
• Batteries: 12 V DC

• 540 x 198 x 395 mm, weight 25 kg

• Accessory box: with adapters for operating the modules for measurements outside the cabinet

The EKD-500 is built into a sturdy metal cabinet measuring 54 x 19.8 (incl. feet) x 39.5 cm. The chassis can be pulled out of the cabinet after loosening 4 screws. The entire unit weighs 25 kg and is drip-proof. In addition to mains operation from 127 or 220 V AC, it can also be powered from a vehicle battery or a battery backup in case of mains failure.

The grill of the small monitor loudspeaker is located at the top left, next to the protective bars / carrying handles. Two multi-pole sockets provide the audio signal for an external loudspeaker or a tape recorder. The upper rotary knob below the loudspeaker is used to switch the AF signal, optionally both channels (channel A, USB, channel B, LSB) can be sent to the monitor loudspeaker or the external loudspeaker in case of ISB (independent sideband) reception, in normal operation with the internal monitor speaker the switch must be in position 4. Just below it is the volume control. To the right is the RF gain control for setting the radio frequency gain, and in the upper right corner is the BFO pitch control for CW reception.

The large ten-digit yellow-green LED display serves as an information centre. The EKD 500 has only a few analogue rotary controls for setting AF and RF gain, the remaining settings must be made via the keypad, and the 7-segment LED display provides information on the receiver status. The EXT LED flashes when the EKD 500 is in slave mode and waits for external control signals; it is lit continuously when the EKD 500 is operated under external control. The first two LED digits provide information on the operation mode and the IF filter bandwidth, coded by a number code for operation mode and bandwidth. Thus „26“ stands for AM reception with the 6 kHz filter and „43“ for SSB reception USB with 3 kHz filter. The letter E in the next segment signals normal reception mode, with the next 7 digits the reception frequency is indicated to the nearest 10 Hz.

With the numeric keypad and the keypad below the frequency display, a reception frequency can be entered directly, the operation mode and the IF filter can be selected, and frequencies can be stored and recalled. The large keys have a long travel, like pressing a button in an escalator.

To enter a frequency directly, e.g. to receive Austrian Radio Vienna on 6155 kHz, press the key sequence F (frequency input) 6 1 5 5 . 0 0 or F 6 1 5 5 E (reception) ore F 6 1 5 5 >. The tuning step width is set with dF 0 . 5 0 is set to 500 Hz for example, and can also be programmed.

To select the operation mode, press MOD and the corresponding digit from the code table, as for AM reception (A3) the sequence MOD 2. In exactly the same way, one of the IF filter positions can be selected with B (bandwidth) and a numeric key. Using the GC function, the AGC decay speed can be changed from fast to slow, to a combination of automatic and manual control, the combination SEL O deactivates the electronic preselector (SEL 1 activates it), so that only a small part of the AM spectrum up to 30 MHz reaches the first mixer.

99 memory locations can be assigned a frequency, the Operation mode and the IF bandwidth, STO 5 E or STO 5 > saves the active setting to memory location 5, CALL 5 > retrieves the memory contents from the display and E (receive) switches the EKD to receive this frequency. CALL 5 E recalls the memory content and activates reception immediately. With the keys CALL98 and CALL99 it is possible to call up a preferred frequency or the distress frequency at the push of a button. SCAN activates various scanning options, whereby the start frequency must be stored in memory location 96 and the end frequency in location 97. EXT activates the slave mode in which the EKD 500 is remote operated, EXT and EXT-FKT pressed simultaneously reset the receiver to the normal operating mode.

You can not only enter a frequency with the numbered keypad, the EKD 500 can also be tuned conventionally with the tuning knob, as described above, the tuning step width is programmable within large limits. The original knob, however, is puny, in the same format as all other knobs on the EKD 500. Above the main tuning knob is another knob that can be used to select the function of the LED row. The LED array serves as an S-meter (each LED corresponds to 10 dB), as an AF level meter and for tuning during RTTY reception. Another LED signals the engagement of the carrier synchronisation during automatic ECSS reception; the EKD 500 also offers this option.

As a professional communication receiver, the EKD 500 is intended for unattended remote operation, it can be remotely controlled and interrogated in all functions from a computer via a modem and a telephone line or can also be operated as a slave from another EKD 500, the memory contents can be changed by remote control or transferred from one receiver to another. The programming is documented in detail in the manual. Another achievement of the microprocessor system is the built-in self-test function. When the EXT and EXT-FCT keys are pressed, a self-test is carried out, AA lights up as an acknowledgement and AO lights up when the keys are released; depending on error messages, further tests can be carried out to assess the functions of individual modules.

In practical use, the EKD 500 impresses with its high sensitivity, the excellent mechanical IF filters and the excellent large signal behaviour thanks to the electronically tracking preselection with small (suboctave) band sections. Since the sound through the monitor loudspeaker is poor, the use of an external loudspeaker is recommended, ideally in combination with a tone control / equaliser and, if necessary, an AF notch filter. The operation takes some getting used to with the key combinations and the fact that the operation modes are only displayed with number codes and not in plain text. However, once you have become familiar with the concept, the receiver almost controls itself, and the implementation of the cryptic operation modes/bandwidth codes is almost subconsciously… The reception performance is excellent in ECSS- AM mode and especially in SSB. Due to the small tuning steps and the rock-solid stability, which is due to the temperature-stabilised oscillator, the EKD 500 can also cope with all special modes such as RTTY and fax reception.

The EKD left the greatest impression on me when I heard Radio St. Helena with my NRD-535, when the signal was very weak and I could only receive fragments of speech and barely identify the English language of the broadcast. I tuned my EKD500 and could understand every spoken word, only the music sounded a bit weird in the ssb mode.

After an input protection lamp, the radio frequency signal from the antenna is fed to the electronical preselector with its sub-octave bandpasses; for scanning operation, the preselector can be deactivated. In a low-noise ring mixer, the received signal is converted to the high first intermediate frequency of 70.2 MHz. After a six-pole monolithic quartz filter, the signal is converted to the second IF of 200 kHz in an active push-pull mixer. After passing the IF filter bank with the steep skirt mechanical filters of highest quality, this frequency is fed to the envelope demodulator in AM mode and to the product detector for demodulation in SSB mode. For ECSS reception and SSB reception with residual carrier, a weak residual carrier is used to optimally synchronise the subcarrier generated in the receiver to the sideband information. With the EKD 500, ISB reception is possible; in this procedure with two telephony signals with different content and common carrier, one programme is made audible on channel A and the second on channel B.

The set is solid state.

• RFT EKD514 on the website of www.radiomuseum.org