Standard Communications Corp., Japan
Standard C 6500 Communications Receiver
überarbeitet am 2.11.2010
The classic "boatanchor" maritime receiver RA-17L was the first
set in 1959 using the Wadley Loop circuitry developed by Dr. T. L. Wadley.
The main principle relies on tuning in to a harmonic multiple of a 1 MHz crystal
oscillator and using this amplified signal for controlling the first mixer, in
which usually a signal from a linear oscillator tuning over one MHz - range is
mixed which will result in the desired reception frequency.
The Standard C-6500 is a desktop shortwave receiver built in Japan in the eighties
using the Wadley Loop circuitry. A signal of an oscillator with a linear frequency
response over one MHz band will be mixed with a harmonic multiple signal of a 1 MHz
crystal oscillator, tuned by the MHz control knob. When the 1 MHz tuning control
reading is combined with the setting of the 000 - 999 kHz dial, You can directly
tune in to the desired reception frequency.
The receiver with it's black metal cabinet has a physical size of 340 x 290 x 156 mm and is portable with it's weight of 6,4 kg, You can easily do an inspection of the inside after loosening 4 screws of the top cover and another four screws of the bottom cover.
You can easily detect the triple tuning variable condensator at the right of the main tuning mechanism / the VFO and the double variable condensator of the MHz - bandswitch left to the middle of the main PCB.
The set can be powered by eight UM-1 cells, 12V DC from a car battery or using 220V AC from the mains. In the top cover, You find the internal telescopic antenna.
The front panel has a very straightforward design: At the left hand of the front
panel, You will recognize the speaker and the headphones socket below. At the right,
You find the tuning knobs on Your right. Select one of the MHz segments using the MHZ
knob, tune within the selected MHz mark for maximum noise. Then use the main tuning knob
to tune in the exact receiving frequency on the 000 - 999 circular dial, You can
read the desired frequency with an accuracy of better then 5 - 10 kHz. Use the PRE-SELECTOR
knob to tune for maximal signal strength.
On the rear, You find the fixed mains lead, the sockets for the tape recorder output and muting, 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. 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 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.
© Martin Bösch 15.3.2008