BT HAWK (CORDLESS TELEPHONE)


Introduced in 1983 the HAWK (illustrated opposite) is British Telecom's first cordless telephone. Available in ivory and brown it consists of 2 parts,

a. A free standing or wall mounted BASE UNIT which is connected to the telephone line using Phone Socket, and......

b. A portable HANDSET that can be carried around the customers premises and will give the user the same facilities as a conventional telephone. When not in use the handset is placed upon the base unit for recharging.

Speech and signalling is transmitted between the handset and base unit using 2 low-power radio links, with a range under ideal conditions of up to 100 metres. Walls and other large obstructions, particularly metal, will reduce the usable range.

Because only 8 pairs of radio channels have been provided for the whole of the UK, then it is possible that HAWK customers living near to each other and using the same radio channels may experience overhearing or other operational difficulties. This is unavoidable, but since the range of the telephone is only 100 metres it is envisaged that this will only happen occasionally.

Although difficulties may be experienced, there is only a slight chance that two adjacent customers will be able to make calls on each others line, even though they may use the same radio channels. This is because during manufacture, a security code is allocated to each base unit and handset so that they become a matched pair. Whenever calls are made or received, the security code is exchanged between them, and the call only allowed to mature if the exchange of code is correct.

Because of the security code arrangements it is not possible to use the handset with other than the base unit supplied.

When received, the Hawk handset will require charging for approx. 24 hours before it is installed, otherwise it will not be possible to test it on site. Read through this guide note fully before attempting to charge the handset. After charging, repack Hawk carefully for transportation to the customers premises.

The main features of the base unit are:-

  • A TELESCOPIC AERIAL which receives signals transmitted from the handset.
  • A 1.5m long WIRE AERIAL used to transmit signals to the handset.
    The positioning of these aerials and the siting of the base unit is important if maximum range is to be achieved.
  • A CALL BUTTON which enables the handset to be called with a distinctive warbling tone. The call button has been provided so that calls answered on a cord telephone on the installation, can be passed to the portable handset.
  • A POWER LAMP which is lit whenever power is connected to the base unit. Power in the form of a low voltage ac. is supplied to the base unit for rectification and regulation from a double insulated plug mounted transformer. The 3m long output cable of the transformer plugs directly into the base unit.
  • An IN USE LAMP which is lit whenever the portable handset is in use or when the call button is pressed. Maximum brightness of the lamp occurs when the transmit aerial wire is correctly positioned.
  • A CHARGE LAMP which is lit whenever the handset batteries are being recharged. A current regulated output is supplied to the handset to recharge its cells from two contacts situated in the handset cradle.

The main features of the handset are:

  • A KEYPAD with last number re-dial (LR) and scratch-pad (P) facilities.
  • A FLEXIBLE AERIAL which folds into the side of the handset when not in use. This aerial is used to transmit signals to the base unit.
  • A FERRITE ROD AERIAL contained within the handset body, which receives signals from the base unit.
  • STANDBY /TALK SWITCH. When in the standby position and switched 'on' the handset is ready to receive calls. Switching to 'talk' activates the handset and answers incoming calls. If an outgoing call is to be made, switching to 'talk' initiates the sending of the security code which ensures that the call will not be originated via someone else's base unit.
  • OFF/ON /HI SWITCH. The handset should be switched 'off' when not in use, or when it is being recharged. The 'on' position is used in conjunction with the 'standby' switch when calls are originated or received. The 'hi' position is used to amplify incoming speech.
  • A TALK LAMP which is lit whenever the handset is switched to TALK.
  • A LOW BATT LAMP which is lit whenever the handsets Ni-cad batteries need recharging. The capacity of the cells is sufficient for 4 hours continuous use, or 12 hours intermittent use. The two contacts situated just above the microphone, engage with those in the handset cradle on the base unit to provide the charging circuit. The 2 sprung clips situated in the handset cradle of the base unit, engage 2 slots on the sides of the handsets switch panel, to help retain the handset in position when Hawk is wall mounted.
  • A BELT CLIP to facilitate carrying the handset about. Note the correct position for the clip on the illustration.
  • The EARPIECE also doubles as the tone caller. The incoming ringing gradually increases in intensity in case the handset is in the vicinity of the users ear.

Base Unit
The base unit has a 47.5MHz RECEIVER. A 4.5kHz detector within the receiver, continually monitors the presence of a4.5kHzsubcarrierwhich is transmitted by the handset to indicate that a call is in progress. Dialling information is transmitted from the handset by interrupting the same carrier at 10pps.

The LINE INTERFACE electrically isolates the telephone line from the rest of the base unit circuitry, and performs the electrical functions of a normal telephone, i.e. impedance matching, regulation, ringing detection, dialling (by relay) and speech transfer to and from the line.

The CONTROL CIRCUIT utilises information from the receiver and line interface to control the transmitter and access to line. A microprocessor and a read only memory (ROM) programmed with the security code are used in this control. Elements of the microprocessor are also used to shape the dialling pulses from the handset.

The 1.7MHz TRANSMITTER develops some 500mW of power. The electromagnetic field near to the output coil which is connected to the transmitters wire aerial, is sensed and then amplified to drive the 'in use' lamp. Maximum brightness of the lamp indicates that the aerial is correctly aligned.

The Handset
An electronic microphone is used to feed speech to the 47.5MHz TRANSMITTER, whose output is connected to the flexible fold down aerial on the handsets side. The 4.5kHz sub carrier used for call control and dialling is generated within the transmitter and combined with the speech and security code signals before modulation and final amplification. The transmitter develops some 10mW of power, with the output being carefully filtered to remove harmonics, particularly those at 95MHz which may cause interference with FM broadcast reception.

Like the base unit, the CONTROL circuitry uses a microprocessor and associated Read Only Memory to send and receive the security code and also to generate the calling tones for the earpiece. The control circuit takes the number information from the keypad and arranged for the 4.5kHz sub carrier to be pulsed at the required rate.

The 1.7MHz RECEIVER utilises a ferrite rod aerial similar to those found in medium /long wave broadcast receivers.


USER GUIDE

Installation of base unit

1. Telephone Connexion
Plug the telephone line cord, from
the base unit, into the BT phone socket.

2. Power Supply
Put the small plug on the power cable into
the socket marked "POWER" on the back of the base unit.  Insert the plug-mounted transformer into the mains power supply and switch on. The "POWER" light will glow.

3. Aerials
The base unit has two aerials, one telescopic and
the other an aerial wire.

Extend the telescopic aerial on the base unit, and arrange vertically.

Extend the aerial wire to its full length.  Remove the handset from the base and put to one side. Depress the "CALL" button on the base unit. This will make the green "IN USE" lamp glow.  Changing the position of the aerial wire will cause the brightness of the lamp to vary.  The aerial is in the ideal position when the glow is brightest; it should be fixed in this position. A vertical position should prove to be best.

(The aerials are finely tuned and should not be altered or changed in any way.  Any alteration will reduce the performance of your Hawk).

The portable handset

Charging

The handset has a rechargeable battery which may require charging for a maximum of 24 hours before use.

A fully charged battery will operate without recharging for up to 3 hours of continuous conversation or for 4-6 hours of intermittent use or for at least 24 hours on standby.  It is charged by setting the handset to "STANDBY" and firmly placing it on the base unit so that the "CHARGE" light glows.

A full recharge - required when the "LOW BATTERY" light on the handset glows - will take a maximum of 24 hours.

It is recommended that the battery charge be kept topped up by recharging at frequent intervals, particularly after long periods of use. You may find it convenient, for example, to charge overnight or while you are out of the house.

Charging may be interrupted to make or receive a call.

Operation
(To make or receive calls make sure the "TALK" switch is set to STANDBY - "ST.BY" and the on-off switch to "ON").

To make a call
1. Rotate the handset aerial to the vertical position.

2. Set the switch to "TALK". The lamp will glow.

3. When dial tone is received dial the number required.

4. At the end of the call, switch to "STANDBY". The "TALK" lamp will go out.  Check that the call has been cleared by switching back to "TALK" and listening for dial tone.  If dial tone is not heard move nearer to the base-unit and repeat unit dial tone is received, then switch back to "STANDBY".

Allow at least 3 seconds between calls.

To receive a call
1. To receive calls the handset has to be switched to "STANDBY" and the on-off switch to "ON".

2. An incoming call will make the handset ring.  To answer, rotate the handset aerial to the vertical position and switch to "TALK".  If the incoming speech is faint switch the on-off switch to "HI".  If the volume is still too low move nearer to the base unit until speech is clearer.

3. At the end of the call switch back to "STANDBY".

Repeat last number
The Hawk automatically remembers the last telephone number dialled.  To repeat that number, set up the call-in the normal way and when dial tone is heard simply press the "LR" button.  At the end of the call switch back to "STANDBY".

Call Facility
1. If an incoming call has been received by the main (fixed) telephone and you wish to pass the call to the portable handset, depress the CALL button on the base unit -- this will cause theportable handset to emit a distinctive tone (if it is in "ST.BY" -  "ON" mode).

2. On receipt of this tone the portable handset user should proceed as in 'To receive a call'.  The fixed telephone handset should be replaced in its cradle.

Belt Clip
A belt clip is included to enable you conveniently to carry the Hawk.

 

 

 
 
 
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Last revised: February 24, 2021

FM