QST, Jun 1962, p. 135.
QST, Jul 1963, p. 130. (340A)
QST, Nov 1963, p. 141.
QST, Jan 1967, p. 131.
The 337 series is an inboard notch filter (the Q-notch) manufactured by Waters Manufacturing, designed specifically for Collins KWM-2 transceivers and 75S-1 receivers. It serves as a solution to eliminate unwanted interfering signals (heterodynes) and adjacent-channel noise without impairing the desired signal.
Models Available:
337-S-1 and 337-M-2 (priced at $33.95 net each).
340-PT (priced at $44.95 net) for transceivers paired with a separate Permeable Tuning Oscillator (PTO).
Design Match: Supplied assembled with matching knobs and escutcheon plates to seamlessly match the original Collins panel aesthetics.
Ease of Installation: Requires no major drilling (except for a single hole in thin aluminum on the KWM-2 using a provided template) and takes an hour or less to install.
Circuit Design: Uses a bridge-T network with a high-Q shunt-tuned coil in the plate circuit of a 12AX7 tube, configured as a cathode follower coupled to a regenerative amplifier.
Provides a narrow, stable rejection notch of 40 dB, and operates over a range of 455 ±2.5 kHz. When tuned to either extreme end to bypass the notch, insertion loss is less than 0.25 dB.
The devices effectively suppresses both sharp heterodynes and adjecent sideband interference by slightly shifting the notch near the edges of the receiver passband.
No version is available for the KWM-2A models equipped with extra crystals for MARS/other frequencies, as Collins used the designated mounting hole for rejection tuning controls in those units.
