2nd IF Amplifier

Reference:    NAVSHIPS 91875(A), para 2h

The second i-f assembly is identical for Radio Receiving Sets AN/SRR-11, AN/SRR-12, and AN/SRR-13.  For Radio Receiving Set AN/SRR-13A the differences are described where applicable.  The connections between these assemblies and associated parts are also different and these differences are described where applicable throughout this discussion.  The second i-f assembly includes filter circuits, three stages of amplification V1001, V1002, V1003 at 200 kilocycles, a BFO mixer, V1004, diode detector V1005, AGC delay diode, V1006, and a cathode follower, V1007 used to supply signals to a frequency shift converter or other accessory equipment.  Link connections are also provided for connecting the AN/SRR-12 or -13 with a companion receiver in a dual diversity reception system.

(1) FILTERS AND INPUT CIRCUIT.  For Radio Receiving Sets AN/SRR-11, AN/SRR-12, and AN/SRR-13, the 200-kilocycle input to the second i-f assembly, appearing at J1001, is filtered before it is applied to the first amplifier, V1001.  The filter selected depends on the position of wafer switches S1001 and S1002 which are actuated by the RECEPTION control.  When this control is set at FSK, A1 BROAD, A1 SHARP, or A3 SHARP, signals are fed through the "sharp" filter Z1001 which provides a pass-band of approximately 3.2 kc centered about 200 kc. When the RECEPTION control is set at A2 and A3 BROAD, the "medium" filter, Z1002, is used which provides a pass-band of approximately 8 kc centered about 200 k-c.

For Radio Receiving Set AN/SRR-13A, the 200-kilocycle input to the second i-f assembly, appearing at J1001, is filtered before it is applied to the first amplifier V1001.  The filter selected depends on the position of wafer switches S1001 and S1002 which are actuated by the RECEPTION control.  When this control is set at FSK, A1 BROAD, or A3 SHARP, the signals are fed through the "medium" filter, Z1015B, which provides a band pass of approximately 3 kc centered about 200 kc.  When the RECEPTION control is set at A1 SHARP or A1 MEDIUM, the "sharp" filter Z1015A, is used, which provides a band pass of approximately 1 kc centered about 200 kc.  Signals are fed through the "broadly" tuned filter, Z1016, when the RECEPTION control is set at A3 BROAD.  Z1016 (together with Z1017, Z1018, Z1011 and T901 of the first i-f) provides a pass band of approximately 8 kc centered about 200 kc.

(2) SECOND I-F AMPLIFIER STAGES.  The first two stages of amplification in the second i-f assembly, V1001 and V1002, are semi-remote cutoff pentodes which are coupled by the broadly tuned transformer circuit, Z1005.  (Z1017 for AN/SRR-13A) The alignment tuning of this circuit is adjusted by means of moving powdered iron cores in L1011 and T1011 (L1015 and L1016 for AN/SRR-13A).   The plate of V1002 is coupled through another broadly tuned transformer circuit, Z1007 (S1018 for AN/SRR-13A) (also provided with iron tuning slugs) to the third i-f amplifier, V1003.  The B section of the r-f GAIN potentiometer R251 is connected to the cathode bias resistors R1006, R1010 of the first two amplifiers, V1001 and V1002, to control the gain through these stages.  The GAIN BAL. control R452 of the AN/SRR-12, or R652 of the AN/SRR-13, variable by means of a screwdriver adjustment behind the hole in the front panel of these receivers is also connected in series with the cathode bias resistors of V1001 ands V1002.  This GAIN BAL. control is used for matching the gain of the AN/SRR-12 or -13 receivers to the gain of a companion receiver when using diversity reception.  This control is not on the AN/SRR-11.

Output from V1003 feeds four circuits: (1) the TUNING meter M451, M651 for AN/SRR-12 and -13, through T1014; (2) the BFO-mixer circuit which is active when the RECEPTION control is set to A1 BROAD, A1 SHARP, or FSK; (3) the diode detector V1005 whose output voltage is fed to the audio amplifier when the RECEPTION control is set at A2 or A3, and whose current operates the TUNING meter M251 on the AN/SRR-11; (4) the cathode follower.

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