E-640, Telefunken E 127 Kw/4; developed and produced by Telefunken, Ulm.
In the Swiss Army, the Shortwave receiver Telefunken E 127 Kw/4 „Rainbow“ carried the designation E-640. It was mainly used as surveillance receiver. In contrast to Germany, where the variant Kw/5 with a frontpanel impact protection grid and connectors on the front was in military use, Switzerland used the commercial model Kw/4 with most connectors on the rear face.
With a size of 550 x 375 x 390 mm and a weight of 44 kg, the device is significantly more compact than the Telefunken E-104 or the Rohde & Schwarz EK-07, the monitoring receiver can be powered from 110 - 240 V AC and with its 8 tubes has a power consumption of 70W.
In the middle of the frontpanel, you find the multi - colour semicircular frequency dial: The band segments are colour coded: the 1,5 - 3,3 MHz range 1 in white, range 2 from 3,2 - 7,1 MHz in yellow, range 3 from 6,9 - 14,1 in grey, range 4 from 13,9 - 22,1 MHz in green and the last range from 21,9 - 30,1 MHz in red.
At the left of the „Rainbow dial“, you find the switchable monitor speaker and at the right the measuring instrument, which can be set to display signal strength or the AF level, as well as the switch for the BFO for CW / A1 reception.
The other controls are located in one row below the frequency dial: from the left the bandwidth selector, the main tuning knob (with fast tuning mode activated when pulled out), the band selector with the identical coloured marks, the RF gain control and the AF gain / volume control.
A the bottom of the receiver's front panel, you find headphones jacks on both sides, and the switches for the noise limiter, the automatic gain control (automatic stands for AGC) and the modes switch, which activates the BFO for CW / A1 morse code reception.
As options, the receiver E 127 can be connected to the radioteletype adaptor TgFs 127 (reception modes F1, F3), the single sideband demodulator BP 102 for SSB reception with full (A3a) or reduced carrier (A3b) and the diversity adaptor Abl 305.
The description of the signal path in the original manual is as follows: „The antenna signal is fed via two HF stages (EF85) with four tuned circuits to the mixer stage (ECH81) where it is converted to the fixed IF of 525 kHz.
The IF signal then passes through two crystal filter stages (EF85) with selectable bandwidths and is fed to the demodulator (ECH81). The BFO is activated for the reception of single sideband or telegraphy signals.
The output stage (EL84) feeds the output jacks and the built-in switchable monitor speaker. A AGC amplifier. The AGC control voltage can be used to drive an adaptor for diversity reception.
The E 127 Kw/4 has been produced in the mid-fifties until the mid-sixties in different variants and has mainly been used by official agencies, for weather reports, press communication and as monitoring and surveillance receiver.
The Swiss Army used the commercial variant E 127 Kw/4 painted in grey with connectors on the rear face.