Narco Mark II Omnigator

  One step in a near-30 year saga of trying to get some 108-118 MHz receiving equipment that was sensitive enough yet would not undergo massive intermod spur generation in the presence of the local 100-kw FM broadcast transmitters.

  This was obtained in mid-1996, but was not ready to be used on 108-118 MHz until November, mostly due to my having to find replacement tubes and get a DC power supply rigged up for it (the included 12-v vibrator one could never put out enough B+).  Being able to remove many "extra" tubes, those associated with only the transmitter or VOR/ILS display, cut down the ma-drain needed considerably.

  Due to physical constraints, the Omnigator ended up being mounted sideways.  The B+ was supplied by the old (de-tubed, except for its 6X4 rectifier) Philmore CR-5AC set, with one half of a 24-v ac transformer having been added for the 12-v Narco tube heater string.  The power and audio was all run thru its cable terminated with an 11-pin "octal" plug.

  The audio line was then run to the Allied 426 stereo amplifier.  In order to use this one channel had to be swapped off from the Realistic TM-1001 tuner (as well the common 5-element Archer FM Yagi) - hardly a one-step process to go between.

  As can be seen, the dial left a lot to be desired for readout accuracy!  I resorted to using the local oscillator of the TM-1001 to zero beat the navaids and adding 10.7 to its dial reading.  The main tuning knob from a Swan was "borrowed" to enable a finer feel than the tiny spin-knob that came with it had given.

  The large dial at the bottom was for the pilot to set a (magnetic) course bearing to a selected VOR.  The left-right meter on the left side would indicate deviation from the chosen VOR radial and LEFT-RIGHT of a selected ILS runway approach (fixed) vector (localizer).  The vibrator supply had also contained a 75-MHz trf receiver that would indicate the crafts passage thru the various OUTER, MIDDLE, and INNER marker (narrow fan-shaped) signals along the runway approach heading.

  As can be seen in the logs and the Real Audio navaid sample files, this setup at times provided excellent signals.  However, on July 29, 2000 mysterious odors and smoke poured from the Philmore supply.  As the Es MUF was raging, I couldn't take the time then to examine just what had gone wrong.  Later tests (outside) couldn't duplicate the situation, but I've never felt confident enough to use it inside since.