[time-nuts] Re; Req: Decent GPS Antenna Active/PassiveRecommendation

[WarrenS]

I agree with John that  "it is a super waste of effort and money" or at the 
very least can be for many.

But for the extreme time-nut, so what?
Being an extreme TBolt nut, and having done this many times before,
I have to point out where a large amount of time and effort can help

>"Do protect the receiver from rapid  temp changes"
    This is always a good idea and easy to do for the most part,
If you want to go total-nuts, and improve things even more, don't let the 
temp change at all. (LH temp controller)


>"The glitches you see will always occur as the receiver switches satellites 
>and cannot be avoided with even the most perfect antenna location"
     If there are "glitches" of any kind at any level, that is an indication 
that something are less than optimal,
because the 'glitches" can be eliminated with "a lot of time, effort, and 
money"
Some of the more typical causes of the big of phase jumps glitches that 
happen when satellites switch are due to:
a) wrong antenna location saved
b) multipath signals,
c) Not enough signal strength
d) Az set too low letting in  poor signals, or too high not letting in 
enough satellites
e) allowing satellites with too low of signal strength to be included.
f) GPS not in fixed location mode.
g) A non choke ring antenna that is letting in signals from below.
f) others ...


>"Set the DF to 1 and the TC to 200 seconds and leave it there. "
Good idea for most with a typical TBolt setup, and good enough for most 
applications,
But it can be made more than a decade better with  "a lot of time, effort, 
and/or money"


>"don't put the thing on the tower. Total waste of effort.
Unless you want to get rid of those glitches when the satellites change.

> "Get a Rb."
Good idea for most, unless you care more about the ADEV noise from 10ms to 
10sec,
which is decades worse in the typical small RB than even a stock TBolt.


> "Unless you can compare the phase of the 10 MHz with a local Rb or Cs (or 
> a good crystal)
> you cannot learn much more or provide better than the short term accuracy 
> of the receiver.
> Improving on this will require a good local standard running open loop."

    While having the proper tools will make things faster and easier, they 
are not necessary.
With an extreme amount time, effort, and experience, It can be done using 
only LadyHeather.
LH has the options that will let you set up a TBolt  good enough to be able 
to test most any Rb or Cs.


There is no single magic bullet fix.
To make a real difference, there is a long list of things that must be done 
and optimized,
and unless you do many things, all of which takes spending a lot of time and 
effort on,
then spending too much time or effort on just one item can be "a super waste 
of time, effort and money"
even for the extreme Time-Nut.

With enough time, effort and/or money, the TBolt's performance can be 
improved to be decade or two better than the typical stock set-up.
So it all depends on now nutty you want to get and how much time to you have 
to spend to make it better.

ws

********************************
From: <johncroos at aol.com>
Sent: Sunday, September 15, 2013 9:50 AM
Subject: [time-nuts] Re; Req: Decent GPS Antenna 
Active/PassiveRecommendation


At least for the T-bolt moving the antenna to a super-optimal location is a 
super waste of effort and money. I suspect this applies to most other GPS 
DOs.

Unless you can compare the phase of the 10 MHz with a local Rb or Cs (or a 
good crystal)
you cannot learn much more or provide better than the short term accuracy of 
the receiver. Improving on this will require a good local standard running 
open loop.

The location should provide tracking of a few satellites - more than 4 if 
possible - but it will remain locked with as few as 1 or 2.

The glitches you see will always occur as the receiver switches satellites 
and cannot be avoided with even the most perfect antenna location. So the 
short term ADEV presented by LH jumps around. Fooling around with the 
damping factor and time constants will not help this much. Set the DF to 1 
and the TC to 200 seconds and leave it there. (or something like those 
values)

The way to get a good standard is to open loop (using you fingers) adjust a 
local Rb such as the LPRO so it maintains a constant phase difference with 
the GPS 10 MHz for a period of hours. Using the time for the phase to change 
a measured number of nanoseconds, the frequency offset between the two is 
easily calculated. There is a HP ap note on how to do this. Use the GPS 
calibrated local open loop standard for all critical work - not the GPS 
output.

Due to lightning considerations here is Kansas - my GPS antenna is in the 
front yard at 6 ft elevation and the N.E FOV is shielded by a 3 story house. 
Result is that the phase as plotted on a strip chart recorder is unchanging 
for hours relative to my Rb, but the flat plot shows phase jumps from time 
to time when the receiver shifts satellites. However the long term phase 
jump always returns to the previous value after the jump.

To make further progress you need a good open loop local standard like the 
LPRO and some way to measure the 10 MHz Phase difference and record it over 
a period of hours.

As to using the pps - I don't know much about doing it that way - however it 
seems obvious that the 10 MHz phase is more sensitive and faster due to the 
greater update rate.  I could be wrong!

Best regards and don't put the thing on the tower. Total waste of effort. 
Get a Rb.

Do protect the receiver from rapid  temp changes -

-73 john k61ql