[time-nuts] homebrew 13 dBm distribution amplifier based on NIST design 5 to 100 MHz

Tom Clark, K3IO tom.k3io at gmail.com
Thu Sep 25 16:02:43 EDT 2008


   Gerhard -- the discussion between you and Bruce has been very
   interesting. I asked a VLBI colleague to look over your design and he
   had this comment.
   In VLBI,  H-Maser frequency standards used to generate local
   oscillators at microwave frequencies. We have problems with amplitude
   modulation being converted to phase modulation when hum is present.  I
   notice that Bruce also uses transformers. Comments from both of you
   will be eagerly awaited!

         Thanks Tom. I notice the Gerhard Hoffmann circuit has a
     transformer on the outputs. Wenzell also uses transformers and we
     have found them to be a problem if there is any stray AC mag. field
     around. We have added some magnetic shielding to the UpDown
     converters to reduce the 60/120 Hz modulation which results if the
     UpDown is close to a another piece of electronics with a AC fan or
     AC transformer. I don't think 60/120 Hz is a problem for VLBI2010
     but it can be a problem for mmvlbi.

   To help to decipher some of our "code words":
     *  the UpDown Converter is a wideband frequency converter that takes
       an arbitrary chunk of 1-20 GHz RF and mixes it to a more convenient
       & standardized frequency to feed a polyphase filter bank.
     *  VLBI2010 is design prototype effort we are doing that will use
       (relatively) small antennas operating over the entire ~2-15 GHz
       spectrum to produce geodetic measurements accurate to mm-levels on
       global baselines (up to ~10,000 km).
     *  mmvlbi refers to VLBI at mm wavelengths (like 100-500 GHz) for
       astronomical measurements. Most recently, the mm observations of
       the size/structure of  radiation from the area around the black
       hole in the center of our galaxy are really exciting.

   Regards, Tom


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