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EKD 300

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überarbeitet am 22.10.2010

Double conversion, 1st I.F. 70,2 MHz, 2nd I.F. 200 kHz

Digital display, accuracy 10 Hz

AM, AM-Sync, USB, LSB, CW, RTTY, ISB

Sensitivity SSB < 0,5 uV Selectivity –6 dB
100 Hz, 500 Hz, 1,4 kHz, 3 kHz, 6 kHz,
2,7 / 3,4 kHz SSB

RF gain, S meter, synchroneous detector, keypad frequency entry

RTTY demodulator (F1)

The EKD 300 is a professional communications receiver produced in the former German Democratic Republic to the need of the Navy and for maritime communications purposes. It's a successor to the EKD100 equipped with decadic switches to select the operation frequency and thus suited for operation on fixed frequencies.
The receiver has been constructed and built by VEB Funkwerk Köpenick (People owned enterprise (VEB) communications engineering company Koepenick) and meets similar demands as commercial receivers made by Telefunken or Rohde & Schwarz (thus sold quite a bit cheaper, specially after the Reunion of the two German states); the military variant has a black frontpanel and green cabinet and the commercial / Navy variant a grey colour front panel and a Navy blue metal cabinet.
The set has been used with the antenna diversity / preselector adaptor EZ 100 quite often.

The receiver has the dimensions 54 x 20 x 39,5 cm and it's weight is 18,5 kg (rack only, without steel cabinet), it's power consumption is 50 Watts when powered from mains 127 or 220 V, the receiver can be alternatively powered from 12 or 24 Volts DC.
The receiver comes with a modular construction with different cases each with several printed circuit boards, all metal cases are connected with cables and are connected to the front panel.

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. 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 +/- 8 kHz crystal filter. After having been mixed to the second I.F. of 200 kHz, the signal has to pass the mechanical I.F. filters, the high quality mechanical i.f. filters found in the EKD 305/315/325 are filters for +/- 50 / 700 / 1500 Hz and a + 300-3400 Hz single sideband filter, in the variants EKD 306/316, the latter is a + 250-6000 Hz ssb filter. For AM, diode demodulation and for single sideband reception, a product demodulator is used. The receiver also has demodulators for F1 / radioteletype modes.

On the frontpanel, You find two multi-connectors for headphones / tape recorder output and for the external speaker. The receiver has also an internal monitor speaker. With the audio distribution switch, the normal telephony signal (TFA - telephony / standard) or the audio signal for the upper sideband in SSB / ISB modes can be sent to the multi-connectors or the monitor speaker. In the TFB positions, the audio signal of the second or lower sideband in ISB mode (A3Bj) is fed to the headphones jack or the monitor speaker. The volume control is the control next to the output connector with symbol with the triangle with an arrow (regulated amplifier) and two waves (audio frequency).
At the right, You find the controls to regulate the R.F. gain (the triangle with the arrow stands for regulated amplifier and the three wave lines for radio / high frequency) and the AGC switch. The symbol "Tau" stands for the time constant of the AGC time, the long and short line for a long or short AGC regulation time ( use short AGC times for AM/A3, A4A and FM modes and long AGC time for SSB / A3A, A3J, A3Ba, A3Bj modes), the hand symbol stands for manual R.F. gain control and there is a switch position in between for combined manual and automatic gain control.
Just abovem You sind the bandwidth selector and the modes switch, both with slightly cryptic symbols. All I.F. filter positions with +/- stand for dual sideband filters used for AM and CW reception, the filter positions +2700 / +3400 are used for single sideband reception of the upper sideband in SSB mode.
For correct operation of the modes switch, it is good to have a minimal knowledge abput the modulation modes used in commercial point-to-point communications. In position A1, the CW (continuous wave) morse code signal is fed to standard audio output TFA. Position A3 is used for the reception of tone modulated telegraphy (A2) and normal AM transmissions; A3A stands for single sideband reception with reduced carries (the receiver will lock automatically in the +/- 50 Hz range to the carrier and the single sideband signal is demodulated and intelligible), A3J is used for single sideband transmissions withoput carrier, the audio signal is fed to standard audio output TFA, too. A3Ba is used to demodulate ISB transmissions (two sidebands with separate informations with reduced carried) and A3Bj for ISB transmissions without carrier, the sideband informations are fed to audio channels A and TFB. The positions F1 /F4 are used for radioteletype communications (frequency shoft keying), according to the signal's mark/space configuration, the signal can be inverted with the switch with the mark facing up or down.

The instrument control selects the different meter modes: in position Y E, the antenna signal strength is displayed, in position UZF the R.F. level, in position 0 dBm the A.F. level from the audio output; there are several other positions to control the receiver's main voltages.
Next to the meter mode selector, You find the main switch, the instrument and the BFO note control to be used in CW reception.

To tune the set, the main tuning knob or the numbered keys can be used, an array of LEDs supports correct tuning of radioteletype signals (F1).
For direct keypad frequency entry, first delete the display with the [X] button and enter the desired frequency with the numbered keys. When You press the button with the symbol with the three waves and the arrow standing for VFO tuning, VFO tuning starting at the entered frequency is activated (button is lit) or locked (button light is off).

For reception of an AM signal under standard conditions, connect the receiver with a sufficient antenna and mains, set the audio selector switch to position TFA (telephony, channel A) and "Internal Speaker". The modes switch should be on A3, the bandwidth switch just next to it on +/- 3000 Hz, the AGC control set to "T long" position. Use the numbered keys or the main tuning knob to tune the receiver to 6.075 MHz and adjust the volume of the transmission coming from Deutsche Welle, Cologne with the volume control, it's the one with the triangle with an arrow and two wave lines; in position UZF, the instrument will display the R.F. signal level.

One problem of the receiver is the lettering of the frontpanel with quite exotic symbols, these might be easy to read for every professional user (remember, this receiver has been in use with East German and Eastern European armed forces where partly kyrillic letters are in use) but might be a bit challenging the listener used to english language lettering. You also have to get used to the fact, that not all filter bandwidths are available in all possible reception modes, for single sideband reception, the upper sideband is fed to the headphones and You have to change the audio channel to "B" for the other sideband. Also the R.F. gain controls (long and short time constant, mixed and manual R.F. gain control might look at bit uncommon, when You use this receiver the first time, but once You get used to it, You will miss all possibilities on other radio ins the future.
After You have mastered all this difficulties, the EKD 300 ist an extremely versatile professional grade receiving instrument; thus I would not recommend to buy such a set when You want to buy Your first shortwave radio. The shortwave reception performance on the bands is excellent with the EKD 300, selectivity and stability are excellent, with very faint signals, the receiver - in my eyes - is able to surpass several semiprofessional receivers when dealing with verys faint signals oo some difficult interference situations (although, there is no passband tuning or notch filter, You might consider buying a Dierking A.F. notch filter).

There is one more drawback: the production quality at the Koepenick plants and servicing of the receiver having been in use for years with Eastern European Armed Forces make this radio a bit unreliable. Contact problems with the audio switch seem a common fault to me, when this occured first, I thought of an operator's fault, and even the other waay round: I thought, the switch might make poor contact and foun in the end, the R.F. gain was set to manual and turned down, etc. You are advised to check the receiver before buying it.
In summary: this is an absolutely professional grade radio often sold for a competitive price if compared with receivers from Rohde & Schwarz or Watkins - Johnson - al lthese are dream radios, but You cannot get them for a sum of 250 - 300 Euros, and for this prie, an EKD 300 can be found. What You get are nearly twenty kilograms of very solid technology with high grade mechanical filters in a communications receiver clearly designed for professional needs.

weitere Lektüre:
d: EKD 315 - Erfahrungsbericht, wwh 5 / 1995

© Martin Boesch 20.9.2010