[time-nuts] Use of dual frequency GPS for NTP server and other purposes

[Tim Lister]

Hi everyone, wanting to pick the collective brains of the group
regarding the use of dual frequency GPS antenna/receivers for NTP time
servers. I work for an observatory that runs telescopes at various
locations around the world and we had previously used Symmetricomm
S250 and S300 NTP time servers to allow remote management and to
provide NTP and IRIG-B signals but these are now affected by the Week
Number Roll Over problem. With the lowering cost of dual frequency
L1/L2 GPS receivers and antennas, I was thinking it would be nice to
have a (likely separate) dual frequency receiver to allow estimation
of the precipitable water vapor above the observatory. Timing
precision needed for the NTP signals is the ~2-3ms expected over local
Ethernet and ~20-50us for a 1PPS output for the future; commercial
solutions rather than homebrew strongly preferred for the time server.

So assuming that there aren't dual frequency time servers or a great
deal of benefit of dual frequency receivers in a time server for this
needed time precision:
1) Is putting a 2 way splitter in front on the time server to split
the GPS signal for the time server and the experimental dual frequency
receiver going to cause issues ? Are there recommended 2 way splitters
that pass L1 and L2 well ?
2) Any recommendations for good quality but not insanely expensive
L1/L2 antenna that will survive being on a pole on a remote high
mountaintop for ~decade ?

Thanks for any input,
Tim