G.E.C. KEYPHONE 91
For Multi-frequency (MF) Signalling
Keyphone 91 provides audio-frequency signalling to the telephone exchange (to
CCITT and CEPT Recommendations). It is based on the GEC746 - the standard United
Kingdom telephone and widely used throughout the world.
A wide range of optional features can be included: PBX recall, ringer volume
control, wall mounting, switching telephone systems (System 100 and plan
105/107), extension telephone arrangements, extension bells, amplified handset,
dial lock, and a range of seven colours.
Apart from the keyset, all components are common to the Keyphone 91, Keyphone 89
and GEC746 ranges of telephones, giving maximum compatibility throughout the
ranges to minimize spares inventory and installation training.
The keyset comprises a 12-button keypad and an audio oscillator. An individual
combination of two frequencies is generated when a key is operated. Twelve
combinations are used (ten for `dialling', and two for extra features). The
pushbuttons have a `fall through' action to ensure positive operation. They are
carefully shaped to assist finger location and minimize `wrong number'
No local power supply is used - the oscillator is powered over the telephone
line from the exchange battery.
ABRIDGED TECHNICAL DATA
TROPICALIZED COMPONENTS THROUGHOUT
NO EXPOSED SWITCH CONTACTS
BUILT-IN VOLUME REGULATOR
SCRATCH AND STAIN RESISTANT MOULDINGS
Case and handset moulded in ABS high-impact plastic. Choice of seven
PVC-covered cadmium-tinsel conductors. Held by stress-relieving grommets.
Line cord - straight; choice of 1.5m (59 in), 2m (78in), or 3m (118in).
Handset cord - coiled; 200mm (8in) unextended, 1.7m (68in) extended.
Multifrequency signalling - two-frequency audio oscillator, line powered;
2-out-of-7 frequency calling, to CCITT recommended frequencies (DTMF).
12 buttons, with black numerals on a white background, arranged in the CCITT
recommended 3+3+3+1 format with 'fall through' action to ensure positive
operation: the extra buttons (* and #) provide, for example, PABX operator
Frequency tolerance + 1.5%
Signal amplitude high group -6 dBm ±2 dB; low group -8 dBm ±2 dB; measured at
600 ohms on a zero-length line. Amplitude differential: high group level exceeds
the low group level by 2dB ±1 dB.
Start-up time within 10ms.
Return loss greater than 14 dB at 600 ohms.
Distortion at least 20 dB below the level of the low-group component.
Line range 1250 ohms for a +2 dBm to -3 dBm level tolerance (48V exchange
battery, 200+200 ohm feed bridge).
Receiver inset - rocking armature; replaceable capsule; sensitivity +55 dB
relative to 1 Pa/rootW.
Transmitter inset: carbon granule, replaceable capsule;
sensitivity -10.5 dB relative to 1 V/Pa at 2 Pa input.
A built-in automatic volume regulator limits speech-signal amplitudes on
lines shorter than 400 ohms; virtually no attenuation on longer lines.
Double coil - DC resistance 10000, impedance at 25 Hz 2000 ohms impedance at
1000 Hz 20 k ohms; accepts ringing currents of between 16 and 30 Hz; bells,
double-gong harmonizing tones: optional bell-volume control.
Suitable for all climates; protected against the entry of insects.
Dimensions Height: 119mm (4.75in) Width: 250mm (10in) over handset; 140mm
(5.5in) over case.
and weight Depth: 216mm (8.5in) over case Weight: 1.7 kg (3.5lb) complete
telephone; 230g (8oz) handset.
Take from The GEC Catalogue Leaflet 5mF879 (Dated 1979)