At one point I contemplated running Andrews "Heliax" for my GPS antenna. Part of the rationale was due to the data presented in page 2 of the following paper. http://ivs.nict.go.jp/mirror/meetings/v2c_wm1/phase_stability.pdf I subsequently decided to stay with my existing run of plenum rated RG58. The bulk of my cable run is indoors where the temperature is fairly stable. Regards Mark Spencer > On Nov 21, 2016, at 12:59 PM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: > > When I first took a look at some of the coax datasheets I couldn't find > anything. I was able to find the following paper "phase stability of > typical navy radio frequency coaxial cables" > http://www.dtic.mil/dtic/tr/fulltext/u2/628682.pdf I attached the table > from the last page. They estimate RG59 to have a tempCo of -330 PPM/degC > for electrical length. They also estimated RG-58 at -480 PPM/degC. > >> On Mon, Nov 21, 2016 at 2:44 PM, John Ackermann N8UR <jra@febo.com> wrote: >> >> I can't find the data right now, but will keep digging. There's also a >> short paper from the early 2000s from Haystack on their measurement of >> LMR400 in an environmental chamber. They came to the same conclusion, but >> I can't find that paper either. :- > > > John, many thanks for the Haystack tip! That is a wonderful paper, I > believe the one you are quoting is "Dispersion and temperature effects in > coax cables" http://www.haystack.mit.edu/tech/vlbi/mark5/mark5_memos/067.pdf > <PhaseTempCo_Coax.png> > _______________________________________________ > 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.

		Attila Kinali

On Mon, 21 Nov 2016 08:22:50 -0800 jimlux <jimlux@earthlink.net> wrote: > I'm not sure about whether an anechoic (which is really "hypoechoic") > chamber is going to get you the data you need. Calibrating the chamber > to the needed level of accuracy might be harder than doing field > measurements. [...] > sin(2 degrees) is 0.034, or -30dB. So a spurious reflection that is 3 > cm different path length (modulo wavelength) and 30 dB down will give > you a 1mm phase center error. 0.1 mm is -50dB. Interesting. I haven't done the math, so I didn't think about that. Yes, the reflections in the chamber would probably limit the resolution. Now I wonder how the calibration data for mass produced geodetic antenna are collected. I very much doubt they put them outside for a couple of days to measure them exactly. Attila Kinali -- Malek's Law: Any simple idea will be worded in the most complicated way.

On 11/21/16 10:10 AM, Tom Van Baak wrote: >> For the equipment hobbyists usually have, the phase center is not that >> important. Most antennas have a variation <5mm. Even 10mm would lead to >> just a ~33ps variation. > > I agree. And besides, for those of us here in Oregon/Washington, the very ground is moving northwest at several inches per year (plate tectonics). > Is that movement in absolute terms? or relative to the NA plate? Where I live in SoCal (on the Pacific plate side ), we also have an annual uplift on the order of 1cm. http://www.unavco.org/software/geodetic-utilities/plate-motion-calculator/plate-motion-calculator.html For 34N, 118W, 47.67mm/yr at 297.53 degrees(CW from north) 22.04N, -42.28E in local coordinates -31.57 X, 30.68 Y, 18.31 Z using WGS 84 for 34, 119W (Ventura county, some 50 miles west) 48.04mm/yr total, -31.12 X, 31.51 Y, 18.62 Z A little less X, a little more Y, because it's starting to "turn the corner"

		Attila Kinali

On 11/21/16 2:58 PM, Attila Kinali wrote: > On Mon, 21 Nov 2016 08:22:50 -0800 > jimlux <jimlux@earthlink.net> wrote: > >> I'm not sure about whether an anechoic (which is really "hypoechoic") >> chamber is going to get you the data you need. Calibrating the chamber >> to the needed level of accuracy might be harder than doing field >> measurements. > [...] >> sin(2 degrees) is 0.034, or -30dB. So a spurious reflection that is 3 >> cm different path length (modulo wavelength) and 30 dB down will give >> you a 1mm phase center error. 0.1 mm is -50dB. > > Interesting. I haven't done the math, so I didn't think about that. > Yes, the reflections in the chamber would probably limit the resolution. > > Now I wonder how the calibration data for mass produced geodetic antenna > are collected. I very much doubt they put them outside for a couple > of days to measure them exactly. That's exactly what they probably do (put them outside) - assuming they have an individual cal at all. A *good* antenna design is one where if the mechanical assembly is within manufacturing tolerances, it will have the same performance as all the others made to the same tolerance. ftp://www.ngs.noaa.gov/pub/abilich/calibPapers/Goerres2006.pdf Note that the residuals after cal were biggest at 0 and 90 elevation, and best in the mid elevations.. > > Attila Kinali >

Note that partial air core (9913) and foam dielectric is better than solid polyethylene. David N1HAC On 11/21/16 5:39 PM, Mark Spencer wrote: > At one point I contemplated running Andrews "Heliax" for my GPS antenna. Part of the rationale was due to the data presented in page 2 of the following paper. > > http://ivs.nict.go.jp/mirror/meetings/v2c_wm1/phase_stability.pdf > > I subsequently decided to stay with my existing run of plenum rated RG58. The bulk of my cable run is indoors where the temperature is fairly stable. > > Regards > Mark Spencer > > > >> On Nov 21, 2016, at 12:59 PM, Scott Stobbe <scott.j.stobbe@gmail.com> wrote: >> >> When I first took a look at some of the coax datasheets I couldn't find >> anything. I was able to find the following paper "phase stability of >> typical navy radio frequency coaxial cables" >> http://www.dtic.mil/dtic/tr/fulltext/u2/628682.pdf I attached the table >> from the last page. They estimate RG59 to have a tempCo of -330 PPM/degC >> for electrical length. They also estimated RG-58 at -480 PPM/degC. >> >>> On Mon, Nov 21, 2016 at 2:44 PM, John Ackermann N8UR <jra@febo.com> wrote: >>> >>> I can't find the data right now, but will keep digging. There's also a >>> short paper from the early 2000s from Haystack on their measurement of >>> LMR400 in an environmental chamber. They came to the same conclusion, but >>> I can't find that paper either. :- >> >> John, many thanks for the Haystack tip! That is a wonderful paper, I >> believe the one you are quoting is "Dispersion and temperature effects in >> coax cables" http://www.haystack.mit.edu/tech/vlbi/mark5/mark5_memos/067.pdf >> <PhaseTempCo_Coax.png> >> _______________________________________________ >> 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.