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E 310 a

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überarbeitet am 23.10.2010

Shortly after the E 309, a single conversion superhet used for maritime communications, Siemens brought out a maritime receiver which saw frequent use in maritime ship-to-ship and ship-to-shore communications in the year 1961. Amongst the maritime wireless operators, the receiver E 310 sonn got the surname "Rainbow" thanks to it's wonderful multicoloured dial.

Double conversion superhet, 1st I.F. 1,18 MHz, 2nd I.F. 100 kHz

Analog dial, max. 1 kHz

AM, CW, SSB (BFO)

(optional 14) 85 kHz - 30,1 MHz

Selectivity -6 dB/ -46 dB
6 / 2 kHz (AM); 1.6 / 0.6 kHz (CW)

Sensitivity
< 0,6 uV CW, < 10 uV AM

RF gain, AGC, Noise limiter, crystal calibrator and 100 kHz fine tuning dial, "magic eye" as signal strength indicator.

The all wave communications receiver has the dimensions of 53 x 33 x 33 cm and a weight of 32 kg in it's rugged steel cabinet with two carrying handles / frontpanel protectors.
The receiver has been available in two variants, as Funk E 310a (Funk E 566) with 50 Ohms UHF antenna connectors and as Funk E 310 b with C Connector jacks.

The most remarkable feature of the E 310 is the big multicoloured impressive frequency dial, it looks like a piece of cake with the multicoloured frequency dials in ascending order from the bottom / inside for the low frequency ranges to the top / outer part with the higher frequency bands. You find backlit band selector pushbuttons in ascending order with the same colours at the left hand of the front panel.
The main tuning knob is located at the left just below the frequency dial. When pulled out, coarse tuning is active, when pressed in, gear is switched for fine tuning. When You press the "EICHEN" (Calibrate) button, the EICHEN window is lit and You hear a calibrator signal every 100 kHz. Then the "FREQUENZLUPE" is active, the "frequency magnifying glass", leave the main tuning on the 100 kHz calibrator point and use the "Frequenzlupe" to tune in a station with the help of the auxiliary 100 kHz dial in the centre of the main frequency dial, it's accuracy will reach 1 kHz.
In the left lower corner of the front panel, You find the mains switch and the fuses are accessible from the front panel.
The volume control is located in the right upper corner of the front panel, just below the monitor speaker. The latter is activated, when the volume control knob is pulled out slightly. Just below, You find the knob for the R.F. gain, the noise limiter and below the reception modes switch. In positions A2/3 narrow and wide, You can select the 2 and 6 kHz I.F. filters, in the A1 / CW mode, the I.F. bandwidth is 0,6 kHz in the VLF ranges 14 - 175 kHz and 1,6 kHz on frequencies above. The BFO control for CW reception and reception of single sideband stations is located at it's left. A nearly unique feature in a commercial / maritime communications receiver is the signal strength indicator: in the Siemens E 310 a green glowind "magic exe" tube is used, and not a conventional meter.

In the VLF ranges 1 and 2, the receiver is designed for CW reception only, in these ranges as well as in the segments 3 and 5 (170 - 350 and 720 - 1540 kHz), the E 310 works as a single conversion superhet with an intermediate frequency of 100 kHz; in range 4 (340 - 730 kHz) and on all higher frequency bands as double conversion superhet with a first I.F. of 1180 kHz. In all these ranges, after the first R.F. stage where also the signal of the 100 kHz crystal oscillator is added, the signal will be mixed to the intermediate frequency of 1180 kHz (when the "Frequenzlupe" is active 1080 - 1180 kHz), in the second mixer, the low intermediate frequency of 100 kHz is generated, L/C filters will have very good qualities when such a low I.F. is in use. The AGC voltage is coupled out at this stage and signal will be demodulated by a diode demodulator for AM, for CW and single sideband reception, a BFO is used. After a A.F. stage and the noise limiter with two antiparallel diodes, the audio is fed to the final audio stage.

The operation scheme of the Siemens E 310a is not that straightforward but easy to learn. In the VLF frequency ranges, the frequency can be read directly from the frequency dial. In the ranges 6 - 12 (above 1,5 MHz), tuning is a bit more comlicated. First select the corresponding band segment, then tune to the next lower 100 kHz calibration point. Activate the calibration function by pressing the red coloured button EICHEN, You can hear the hiss of the calibration oscillator, press the main tuning knob in for fine tuning and tune to zero beat of the oscillator signal, that means the beat frequency will have a lower note and will disappear in one moment. Now press the button FREQUENZLUPE to activate the fine tuning dial / interpolation oscillator; on the semicircular dial, You can carefully tune to the correct kHz digits of the desired reception frequency using the FREQUENZLUPE fine tuning knob. You must not touch the main tuning knob again.
This might sound a bit complicated but is not so complicated in practical use: press the Band 7 button, then activate the calibration oscillatorwith the button EICHEN, use the main tuning knob to tune for zero beat on the 6,1 MHz dial mark. The press the FREQUENZLUPE button and tune with the fine tuning mechanism to "55" on the small semicircular dial and You should arrive at receiving Radio Vienna on 6155 kHz. When You move the main tuning knob, the "FREQUENZLUPE" knob pops out and the fine tuning mechanism is switched off.

The E 310 shows a very good performance for AM fixed frequency reception and for CW reception in the VLF bands, it is a good performer for mediumwave DXing as there is no permanently switched attenuator for the mediumwave band.
Nowadays, SSB reception with the help of a BFO is not state of the art anymore, but it was standard, when the receiver was new in the sixties. The skirt selectivity of the L/C filters is adequate but performance may not reach the results of a set with high quality mechanical filters. Like in other German commercial receivers, You miss features to improve reception under difficult conditions as a passband tuning, notch filter or a tuneable crystal filter.

© Martin Bösch