The Siemens RK-641 is technically equivalent to the Sangean ATS-803, the receiver is a PLL-controlled double conversion superhet built by Sangean in Taiwan. On behalf of Siemens, the front panel was adapted in a fancy black and gold colour scheme and the frequency range was limited to the FTZ-compliant upper limit of 26.1 MHz. Even though Siemens representatives at the electronics fairs claimed that the Siemens set, which had a much higher price tag, was not only a re-labelled Sangean, it was never prooved that the set with the brand of the German quality manufacturer was a better performer. In any case, this is a consumer class radio, which cannot be compared with the commercial receivers from Siemens.
The Siemens RK 641 has a plastic cabinet with dimensions of 310 x 160 x 60 mm and a weight of about 1 kg, similar to the Sony ICF-2001, and a 1.38 m long built in telescopic antenna. The set is powered from six mono cells UM-1 or a 9 V external power supply. Two UM-3 AA cells are required to operate the quartz clock and to store the frequency memories.
The set is switched on with the power button at the top right of the front panel, underneath are the slider controls for volume, stereo balance (although stereo can only be heard when headphones are used), treble and bass. Below are the rotary controls for the BFO (heterodyne oscillator for A1 / single sideband reception) and the RF gain, which must be at the right full stop for normal operation.
Further below are the switches to lock the keyboard (LOCK), to acitvate the BFO and VHF stereo. This switch is an important characteristic: if it has the second function to switch between two IF bandwidths (WIDE / NARROW), you have the improved A version of the receiver with the narrow IF filter in front of you - pay attention to this detail when buying at a flea market.
The five frequency ranges can be directly called up: the FM key selects the FM broadcast band, the AM key selects the continuous AM frequency range from 150 - 29'999 kHz. The LW key selects the longwave band (150 - 281 kHz), the MW key the mediumwave band (520 - 1620 kHz) and the SW key the shortwave band. Repeated pressing of the SW key calls up the next shortwave broadcasting band and the last active frequency in this band, thus providing an additional frequency memory in each radio band, in addition to the nine frequency memory channels. To store the active frequency, press STORE and the memory channel number; to recall a stored frequency, press CAll MEMO and the corresponding numeric key.
START/STOP activates automatic scanning, which stops as soon as a station with sufficiently signal strength is tuned. Pressing the START/STOP key again stops the search or continues the station scan.
With the BFO ON/OFF switch, the BFO can be activated for receiving CW or SSB transmissions, for example from radio amateurs; ECSS reception (i.e. receiving an AM shortwave station using SSB mode and tuning to „zero beat“) is difficult due to low frequency stability and wide tuning steps.
A ferrite antenna is built in for long and mediumwave reception. In addition to the built-in telescopic antenna, there is also the option of switching to an external antenna for VHF and shortwave reception.
With the built-in digital clock, a SLEEP timer can be programmed for 90 to 10 minutes until switch off, and the radio can also be used alarm clock.
When the set came out, the Sangean ATS-803 was a much cheaper alternative to the original Sony ICF-2001. In this „clone“, Sangean incorporated some improvements long-awaited by shortwave listeners. The set was sold, partly with modified IF filters, by various discounters and also as Siemens RK 641 or in the A version with two IF bandwidths as RK 651. In Switzerland it was sold at Interdiscount as Intersound WE-12.
Double conversion, microprocessor control with PLL synthesis circuit.
The set is equipped with semiconductors.