[time-nuts] Cable delay correction for Tbolt Cs substitude
John Ackermann N8UR
jra at febo.com
Sun Oct 16 13:51:00 EDT 2011
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:
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.
On Oct 16, 2011, at 1:32 PM, "WarrenS" <warrensjmail-one at yahoo.com> 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.
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