FL4
- 136 -
FL4/3
Cut-off 3.4kHz to reduce interference on transatlantic
music circuits. Used at BH Control Room. DD 1958.
OBSOLESCENT.
FL4/4
Cut-off 10Mc/s. Mounts on CH/34. Used to reduce noise on
20Mc/s radio link. DD 1958. OBSOLESCENT.
FL4/5
483mm x 89mm panel mounting 4 filters for rejecting 20kHz.
DD 1959. TI.T.lO. OBSOLESCENT.
FL4/6
Used on carrier phantom circuits to prevent high
audio-frequency crosstal~ from P.O. carrier systems.
Cut-off frequency 11.5kc/;. Z in and Z out: 600~. 76mm x
5lmm x 76mm. DD 1960/52. DD Spec 2.132. DDHB 2.93.
TI.L.3. OBSOLESCENT.
FL4/7
Switchable Lowpass Filt~r first used at Tatsfield.
Includes two 600~ lowpass filters cutting off at 3.5kc/s
and 5.0kc/s respectively switched in or out by relays.
Can be mounted on standar,l 483mm x 222mm panel or suitable
shelf on control
desk.
DD 1960/62.
DD Spec 2.167.
OBSOLESCENT.
FL4/8
Used for noise measuretlents at VHF/FM
stations to attenuate unwanted frequencies
when a VHF/FM signa:. is demodulated.
DD Spec 2.191. OBSOLESCE1IT.
transmitting
which occur
DD 1960/62.
FL4/l0
Used on the sound channel of SHF television point-to-point
links to remove line freqt,ency of 10.125c/s and its second
harmonic. l87mm x l2lnml. DD 1960/62. DD Spec 2.212.
OBSOLESCENT.
FL4/11
FL4/l2
Replaces FL4/l0. DD 1963. OBSOLESCENT.
Has negligible loss at 44Cc/s and at least 30dB loss at
800c/s and above. Balanced 600~ circuit. l84mm x l2lmm x
83mm. Used with programme failure alarms. DD 1964.
DD Spec 2.215. OBSOLETE.
FL4/l3
Used on Eggardon Link Switching System. Cut off: 2300c/s.
CHl/18D. DD 1964. DD Spec 2.228. OBSOLETE.
FL4/l4
Lowpass Filter in small cDpper box
reduce unwanted modulatio~ products
and vision signals. DD 1964.
OBSOLESCENT.
used in MDl/502 to
in combined VHF sound
DD Spec 4.21. ACO.
FL4/l4A
Similar to FL4/l4 less metal box and coaxial connectors.
Used for 37.5MHz IF only In MDlM/507, MDlM/507A. Printed
board. DD 1971. WITHDRAW:~.
FL4/15
Lowpass Filter used in MDl/503A operating on 405 line
vision and AM sound to r,~ject second and third harmonic
components of the c,irrier frequency. DD 1964.
DD Spec 4.47. DDTM 6.144 ('77) . ACO. OBSOLESCENT.
FL4/l6
Band II filter formerly coded 50L25.
Used on BA13/9.

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