FL4
FL4/34
FL4/35
FL4/36
FL4/37
FL4/38
FL4/39
FL4/39A
FL4/40
FL4/41
FL4/42
FL4/43A-F
FL4/44
- 138 -
Used in Switching System (in particular
Manchester-Newcastle indicHtion of Serck System condition)
where signals are to be p~.ssed over a carrier channel
above both voice and telegraph signals. CH1/18C.
DD 1968. WITHDRAWN.
Lowpass Filter used on L(mdon
system to remove 8.2kHz !:igna1
31. DD 1968. WITHDRAWN.
to Droitwich signalling
tone. CH1/18C, pegs 17,
Used in MNlL/5 to limit the bandwidth of programme
material applied to a carr:.er programme circuit to enable
a 10kHz tone to be added. CH1/18. DD 1968. WITHDRAWN.
Lowpass Filter, 100kHz,
vo1tages from output of
DD 1968. DD Spec 5.161.
:'5n, used to remove unwanted
]~5M/6. CH1/12A, pegs 24, 36.
OBSOLESCENT.
Lowpass Filter, 100kHz, for removing out of band noise
when doing measurements on stereo systems. Similar to
FL4/37 but with 600n impeclance instead of 75n. CH1/12A.
DD 1968. DD Spec 5.161. OBSOLESCENT.
Simple Lowpass Filter, 2:1kHz, used as alternative to
FL4/33 where attenuation 0:: 23kHz need not be so great and
where a low insertion loss is required. CH1/12A, pegs 14,
33 as for FL4/33. DD 1968. ACO. WITHDRAWN.
Simple Lowpass Filter, 2:1kHz, used as alternative to
FL4/33 where attenuation 0:: 23kHz need not be so great and
where a low insertion loss is required. CH1/12A, pegs 14,
33 as for FL4/33. Has additional rejection at 19kHz.
DD 1970. OBSOLESCENT.
Lowpass Filter, 2700Hz, uSI~d to remove the signal tone of
2700Hz from the speech pat:l in the remote switching system
between Birmingham and P,~terborough and between Norwich
and Peterborough. CH1/18C. DD 1969. WITHDRAWN.
Aural Monitoring Lowpass Filter used to remove tones
associated with Automatic J10nitoring and provide a clean
programme. Switchab1e to) 6 different pairs of tone
frequencies. Includes small amplifier. CH1/18E.
DD 1969. DD Spec 2.295. I)BSOLESCENT.
Lowpass Filter, 15.625kHz and 22.0kHz used to remove
15.625kHz line frequency and 22kHz pilot frequency from
the output of receivers f~eding transmitters. Unbalanced
600n to 600n. Eddystone b)x with plate for fixing at side
of bay. DD 1969. DD Spec 2.296. OBSOLESCENT.
Lowpass Filters used in OT1/3. Suffixes indicate
frequencies 3.1kHz, 3.7kH~, 6.2kHz, 12.6kHz and 9.6kHz
with improved stop-band attenuation. CHI/54. DD 1969.
DD Spec 2.304. DDHB 2.184. OBSOLESCENT.
Used in PA18M/15 to e1imLnate speech frequencies from
control channel, and in PA18M/14 to eliminate control

38