Update on crystals for Phased-Locked Oscillator Bricks
        
                N1BWT Nov. 1996
                
        Most of the PLO bricks we've seen are electrically equivalent
        to the Frequency West units; these include California Microwave,
        Loral, and others.  The same crystals, with a x108 multiplier
        for 10 GHz, work fine in all of them.
        
        There is one exception: some PLO bricks made by MICROMEGA.  These
        bricks have a WR-90 waveguide output and come in two variants,
        a model number ending in -A uses a x104 crystal multiplier, and
        a model number ending in -B uses a x112 crystal multiplier.  If
        the current output is in the desired frequency range, then a new
        crystal may be ordered with no further changes.  I order to the
        same International Crystal Catalog No. 585155 as the Frequency
        West bricks, simply specifying the desired crystal frequency.
        
        The MICROMEGA bricks are also much easier to retune than other
        varieties, since the output filter is a waveguide filter.  All
        but one of the tuning screws are readily available in the output
        waveguide; the last screw is under the multiplier cover.  Taking
        the cover off and reversing it puts a hole in just the right
        place.  
        
        Most of the MICROMEGA bricks may be retuned low enough for 
        low-side LO injection on 10 GHz, using a x96 crystal multiplier,
        just by carefully retuning the output filter.  
        

        CAUTION:  Even though the crystal is multiplied many times, 
        high VSWR on the output can pull the frequency tens of KHz
        and even cause instability.  An isolator or attenuator will
        cure this problem and usually result in an output frequency
        closer to desired.  Since most bricks have more than enough
        output, an attenuator does the trick.
        
        NEVER try to get the brick exactly on frequency with the
        crytal trimmer.  Adjust it for maximum indicated output on
        the "XTAL" terminal to get best frequency stability, and
        it will still change a few KHz with mountaintop temperatures.