FL4/17
FL4/18
FL4/19
FL4/Z0
FL4/21
FL4/22
FL4/23A-D
FL4/24-29
FL4/30
FL4/32
FL4/33
- 137
FL4
DD 1965. OBSOLESCENT.
Band 11 filter formerly coded 75L26.
DD 1965. OBSOLESCENT.
Used on BA13/9.
Used on carriet phantom circuits to prevent high audio
frequency crosstalk from PO carrier systems. Cut off
frequency 11.5kH2. Z in and Z out: 600~. Sub chassis for
fitting in CH2/l. Replaces FL4/6 in transistorised
control
rooms.
DD 1965.
DD Spec 2.255.
TI.L.3.
OBSOLESCENT.
Used in MN2M/l to confine a programme signal to a
designated. frequency spectrum. CHl/18A, pegs 23, 28.
Replaced by FL4/23. DD 1965. DD Spec 5.114. OBSOLETE.
Used on PA6M/49, PA6M/50 and PAlM/50 to filter out 2587c/s
and
2868c/s.
CHl/18C.
DD 1965/67.
DD Spec 5.114.
WITHDRAWN .
Used on PAlM/51. CHl/18C. DD 1965/67. WITHDRAWN.
Lowpsss Filter used in MDlM/505 and also as alternative to
FL4/14
in
some
cases.
Printed
board
64mm x
38mm.
DD 1965/67. DD S~ec 4.48. WITHDRAWN.
600~ Balanced Low)sss Filter used with MN2M/3-6. Cut off
frequency 9.25kHz~ Replaces FL4/l9. Band D versions are
for use with asso~iated filter FL3/8 and A and C versions
are not. A ani B versions provide extra rejection.
CH2/2. DD 1967. DD Spec 5.139. ACO. OBSOLESCENT.
Similar to FL4/23 but with cut off frequencies of
10.25kHz, ll.25diz, l2.25kHz, l4.25kHz, 7.25kHz and
8.25kHz respectiv~ly. Used in association with FL3/9-l4.
Suffixes indicat~ different versions. A = additional
filter section; B = additional filter section and
complementary to associated highpass filter; C = without
additional filter; D = without additional filter section
and complementary to associated highpass filter. DD 1969.
DD Spec 11.113 (701 FL4/26, 11.114(70) FL4/27, 11.115 (70)
FL4/29. ACO. OB:;OLESCENT.
Lowpass Filter, 7.lkHz, used on Open University
transmissions to remove monitoring or switching tones at
7.6kHz and 7.8kHz before transmission. Includes amplifier
to give overall unity voltage gain. CHl/18C, pegs 45, 66.
DD 1970. DD Spec 2.337. DDTM 2.230. OBSOLESCENT.
Lowpass Filter, 10kHz, used on Bristol-Mendip remote
switching system to prevent transmission of signalling
frequencies. SaIle printed board as FL4/21. CHl/18.
DD 1970. WITHDRAvlN.
Lowpass Filter used to remove all monitoring tones above
18.5kHz from thE input to a transmitter fed from a VHF
rebroadcast recei\er. Supersedes FL4/5. CH1/12A, pegs
14, 33. DD 1967. DD Spec 5.138. ACO. OBSOLESCENT.

37