I wouldn't think the cable type will make an order-of-magnitude difference. Referenced in the Haystack note is another paper that goes through the theoretical derivation that produced the "expected results" column. I think it's the same URL but 067.pdf as the file name.
John On Oct 16, 2011, at 2:21 PM, "WarrenS" <warrensjmail-...@yahoo.com> wrote: > Thanks John > > Any chance using 75 ohm cable (as suggested in the Tbolt manual) like RG6U, > when used in a 50 Ohm system could be orders of magnitude worse than LMR-400? > Sounds like may be time to do some controlled cable experiments comparing > different cables. > > I do know that Cheapie GPS timing antenna's can have a large Phase variation > when the Sun hits them. > I had one antenna that changed 25 ns every day around Noon time. > That is when I changed over to a Symmetricom 58532A antenna and things > improved 10 fold. > With the new antenna the phase error change is now down at least near the GPS > noise level, > but it seems to still have some "antenna system" temperature effects. > > Maybe a silly question but how can a 1.5GHz preamp and filter change the > phase over so many cycles? > > Does anyone ever add a temperature controller on the antenna? Maybe that > should be my next test. > > ws > > ****************** > > from John Ackermann N8UR > > I did some very rough measurements last summer with. Run of LMR-400 that was > laying on the roof in the hot Georgia sun. > Using a network analyzer to "ping" the cable I found the day vs. night delay > difference was pretty much in the noise. I'll see if I can find the details > and if so will post them. > > I found via google a brief paper from Haystack that measured LMR-400 and > LMR-240 and found in the range of -11 to +17 ppm/K of the total cable delay. > They note that 9 ppm/K is about 3ps/degree in 100M of cable: > > http://www.haystack.mit.edu/tech/vlbi/mark5/mark5_memos/069.pdf > > However, there's another possible tempo contributor that I suspect could be a > significant contributor, and that's the preamp up in the antenna, > particularly if it has a bandpass filter. It wouldn't surprise me at all if > preamp/BPF tempo was noticeable. > > John > > ************************ > On Oct 16, 2011, at 1:32 PM, "WarrenS" wrote: > >> Anyone know what the propagation delay temperature coefficient is for RG6U >> coax and how much it varies between different brands of cable? >> >> In my efforts to improve the Tbolt's performance to make it into a better Cs >> substitute, >> test suggest that the temperature coefficient of the antenna lead-in cable's >> propagation delay is contributing to diurnal errors. >> >> Anyone have a idea for a SIMPLE & cheap voltage controlled delay line that >> can be changed by a few ns as a function of the outside air temperature? >> >> As an alternative, Mark, want to consider adding another LadyHeather >> feature that tweaks the Tbolt's cable delay value as a function of the >> outside temperature? >> If interested, I have a couple ideas of how to get the outside temperature >> to LadyHeather. >> >> ws >> >> _______________________________________________ > > > _______________________________________________ > 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.
