Hi Here is some actual RF data on a number of antennas:
http://www.ngs.noaa.gov/ANTCAL/ There also is a pretty good document on how the calibration is performed. It appears that if you are after ps or mm then a calibration file on the antenna type being used is needed. Pointing north to be able to use that file would be a requirement. If we ever get into the sub ns world for Time Nuts time transfer, calibrated antennas may be needed. ———— *IF* an uncalibrated antenna is much worse than the survey antennas, then you might get into the couple of ns level as the sat’s moved around. Still not a real big deal for a GPSDO. Un-corrrected ionosphere issues versus angle will be a larger issue. Bob hOn Dec 17, 2014, at 8:49 AM, Jim Lux <[email protected]> wrote: > > > On 12/17/14, 4:36 AM, Bob Camp wrote: >> HI >> >>> On Dec 17, 2014, at 1:07 AM, Chuck Harris <[email protected]> wrote: >>> >>> I would venture that the extent of the magic was to note the physical >>> center of the array, and call that the phase center. >>> >>> As long as you always orient the antenna in the same direction, any >>> errors that might exist in the real phase center will be consistent, >>> and could be corrected for by noting the offset from a benchmark. >> >> I’m afraid that’s what they do as well. Just spin it and see what a dial >> indicator reads sort of thing. I think that I’d want something that actually >> did some microwave tests …. >> >> B > > The UNAVCO data is an actual RF test. > > And from a manufacturing standpoint, I would imagine that typical tolerances > are better than 0.001" (25.4 microns). Changes much bigger than that would > show up as VSWR changes, which *is* something that they check in > manufacturing. > > The Leica "artichoke" multiband choke ziggurats (they're not flat, so I have > a hard time calling it a "ring") are cast and then machined. Casting isn't > what I would think is a precision operation, but it probably is real > consistent from unit to unit. > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
