403 -
UN20
UN20/9
Two-tone Detector Unit
Remote Switching System.
DD 1967. WITHDRAWN.
used for the
CHl/18 with 2
Washford-Cardiff
detector units.
UN20/l0
Polarity Detector Unit used with GE4/l to test the
polarity of the left and right hand channels of a
stereophonic circuit. Box l2lmm x 95mm. DD 1967.
DD Spec 2.340. DDTM 2.193. EDI. OBSOLESCENT.
UN20/l1
Tone Detector Unit used to detect LF tone from a distant
UN8/l0 as part of a system to indicate when Radio 1 and
Radio 2 are using common programme material. CHl/18A.
DD 1967/68. WITHDRAWN.
UN20/12
Tone Detector Unit used at the receiving
London/Droitwich signalling system to detect
from UN8/12. CHI/18C, pegs 17, 33.
WITHDRAWN.
end of a
8.2kHz tone
DD 1967/68.
UN20/13
Carrier Drift Detector Unit used in MNl/6 to compare the
locally derived 10kHz tone with that extracted from
incoming programme material. Outputs operate a chart
recorder and operate an alarm when the frequency
difference exceeds a predetermined limit. DD 1967/68.
WITHDRAWN.
UN20/14
Differential Detector Unit used in MN2M/7 to compare the
outputs from 2 UNl/105 and initiate an alarm when the
difference exceeds a predetermined amount. CHl/12A, pegs
22, 31. DD 1968. DD Spec 5.151. ACO. OBSOLESCENT.
UN20/15
Tone Detector Unit comprising 3 tone detectors with 3 d.c.
outputs and a fourth d.c. output for a reset control when
no tone is received. BBC/ISEP card with 25 way connector.
DD 1968. WITHDRAWN.
UN20/16
Detector Unit used in EP9L/1 to check the output levels of
the two associated OS2/35 and initiate changeover from a
faulty
oscillator
to
a
spare.
CHl/12A.
DD 1968.
DD Spec 5.147. ACO. OBSOLESCENT.
UN20/l9
Change of State Detector Unit operated by a transient
pulse from UN23/7 to enable the pulse to be lengthened to
some 2 seconds and powered sufficiently to connect a tone
source to line by relay to signal back to the sender that
a message has been received. Related units are UN23/4,
UN23/5, UN23/6, UN23/7, UN23/8, UN20/l5. ISEO board with
25 way connector, coding positions 3, 11, 23. DD 1969.
CANCELLED.
UN20/20
Dual Tone Detector Unit used in EPlM/ll, EPlM/12
a burst of tone at either 2.6kHz or 6.5kHz and
logic 1 to UN23/9 to acknowledge the receipt of
message. 25 way ISEP plug, coding 3, 13, 19.
CANCELLED.
to detect
deliver a
a digital
DD 1970.
UN20/2l
Vioce Frequency Detector Unit, 1000Hz, used in the system
for preventing automatic line tests from starting up

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