[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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