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 _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.