Hi A lot depends on just which outfit you buy your attenuators from. There certainly *are* outfits out there that supply you just over 20 db RL when the spec is 20. They also don’t charge very much for their attenuators ….
Bob > On Sep 4, 2017, at 4:53 PM, jimlux <jim...@earthlink.net> wrote: > > On 9/4/17 1:18 PM, Wes wrote: >> >> >> If these are COTS attenuators, their own return loss is unlikely to be >> 40 dB. In fact grabbing an old HP catalog off my bookshelf (I'm dating >> myself) I see a typical type N attenuator specified as 1.2 VSWR (~21 dB >> RL). I went on a quick "shopping" trip looking for an L-band, type N >> bias tee. I'll spare you the links, but typically they are also rated >> at 1.2 VSWR. >> > > Be careful, that's the "catalog spec" which means "what we can inexpensively > measure".. > > It's like SMA connectors, which are specified at 1.05:1 or 1.1:1 and <0.3dB > loss. > https://www.amphenolrf.com/connectors/sma.html > > > In reality, they are a LOT better, it's just that measuring that in a > production environment is tough. > I'd not want to set up a manufacturing test set that measured loss with an > uncertainty of 0.01 dB. > > I'll point folks to: > Jesch's paper in 1976 > > http://ieeexplore.ieee.org/document/6312234/ > > > > and then Maury > https://www.maurymw.com/pdf/datasheets/5A-021.pdf > > Someone at Maury did a paper which I can't find right now where they measured > a bunch of SMA connectors over hundreds if not thousands of mate/demate > cycles. > > > RF cafe has a nice summary > http://www.rfcafe.com/references/articles/Joe-Cahak/rf-connectors-cables-joe-cahak-6-2014.htm > > > > > > >> Perhaps NIST, with an unlimited supply of tax money, splurged and >> manufactured bias tees with >40 dB RL. Maybe they did the same with the >> attenuators. We'll never know because they didn't provide an equipment >> list or a measurement procedure. They said nothing about the cable >> either, other than they started with RG-58 and replaced it with "better" >> cable. > > But you could probably send an email to the author and ask. NIST, like JPL, > is one of those places where people work forever. Tom Otoshi, who wrote a > report on N connectors in 1963 cited by Maury, above, still works at JPL (I > think.. I confess I haven't seen him recently, he might have retired, but he > was certainly around in the last 10 years), and given the span of years, that > N connector work was probably when he was a just out of school engineer. > > > > > > > >> >> A few words about cable, since that is what this discussion is all >> about. Cable, regardless of type and manufacturer, has its own RL, also >> known in that business as Structural Return Loss (SRL) See: >> https://www.belden.com/docs/upload/hdcarltp.pdf and >> http://www.keysight.com/upload/cmc_upload/All/E206COMPTEST_METHOD.pdf. >> >> At least the authors admit, "Thus far we have seen little difference in >> the data." >> >> Wes >> >> >> On 9/3/2017 3:02 PM, Bill Byrom wrote: >>> For precision timing measurements, I would think that there would be >>> concern about the double reflections of a badly mismatched low loss >>> transmission line (such as using 75 ohm line in a 50 ohm environment). >>> The re-reflected signal will act similar to multipath (as a delayed >>> aggressor) on all satellite signals equally. The impedance mismatch >>> delayed reflection aggressor could aggravate timing errors due to >>> changes in temperature or stress in the cable. Whether this is important >>> for you depends on how time-nutty you want to get. >>> >>> See these papers: >>> >>> Effects of Antenna Cables on GPS Timing Receivers: >>> http://tf.boulder.nist.gov/general/pdf/1384.pdf >>> >>> Absolute Calibration of a Geodetic Time Transfer System: >>> http://xenon.colorado.edu/paperIrevise2.pdf >>> -- >>> Bill Byrom N5BB >>> >> >> _______________________________________________ >> 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. > > _______________________________________________ > 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. _______________________________________________ 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.