Century - 21
überarbeitet am 19.10.2010
In the eighties, a shortwave receiver from the Far East has been sold in
several ham radio and electronics shops in Germany, but it's designation
Century-21 made it difficult, to establish a relationship to a well known
radio manufacturer in my mind. The set turned out to be of a similar contruction
to the Drake SSR-1 and probably technically almost identical to the Standard
C-6500. Maybe one of the readers might have a better understanding, which
company was the actual manufacturer of the set.
The set has a physical size of 340 x 290 x 156 mm and is portable with it's
weight of 6,4 kg, but it's not really a delight to carry it around when going
abroad for holidays. It's rugged metal cabinet is quite easily accessible and
there is aufficient room for modifications in the inside. Fitting the parts
of a Century-21 cabinet together is a real pleasure compared to doing this
to a Sony ICF-6800W.
The front panel has a very straightforward design, but the operation might seem
a bit tricky, if You're not familiar operating a set based on a Wadley loop circuitry.
On the rear, You find the fixed mains lead, the telescopic antenna and the sockets for the tape recorder output, the muting socket, the antenna and earth terminals and the fuse.
Operating the set will be an easy task, when You get used to the Wadley loop
receiver's philosophy - if not, You might consider a badly detuned set as defective.
The set uses the Wadley Loop principle developed by T.L.Wadley and used in Racal's RA-17L for the first time. From a main crstal oscillator, the receiver tunes in to harmonic multiples of the 1 MHz oscillator crystal in the range of 45,5 - 75,5 MHz. A 42,5 MHz oscillator will mix down this signal to an intermediate frequency of 2,5 MHz and this signal will be mixed with the one of a tuneable 2 - 3 MHz VFO, this will determine the 000 - 999 kHz digits of the reception frequency. The intermediate frequency will me mixed to 455 kHz and after passing the I.F. filters and amplification, the signal will be demodulated.
In practical use, the Century-21 will have an impressive sensitivity to
wake signals, it works well with the telescopic antenna and a random wire antenna,
long wire and active antennas might cause overloading and will require attenuation
of the signal using the RF gain control. When a signal will appear very faint,
the signal strength might really be poor due to receiving conditions, the maximum
of the MHz - control might be out of tune, the preselector might be out of tune or
switched to the wrong band, the RF gain control might be reduced - but the risk of
forgetting one control in a bad setting is high. Quite often You might encounter
the calibration of the main tuning control 1 - 3 kHz out of tune, You might correct
this carefully adjusting the L21 coil.
© Martin Boesch 15.3.2008