I have sold over 200 T-bolts and had to replace about 30 of their thermometer chips,
most because of the revision problem causing the 'stepped' temp plot, but some
because of chip failure. If this were the typical low res problem the yellow trace
would show the characteristic uniform staircase steps, not the random jumps to
some common  value that it never exceeds. If you look closely at the plot you'll
see many very small changes that are far smaller than any of the steps would be.
Also there are major portions of the trace where it is absolutely flat and I doubt that
this is really happening. I'll stick with broken but maybe someone else with another
NTBW50AA can run LH and show what their graph looks like.

-Arthur

Hi

I have quite a few of these and they all produce temperature plots that look like proper TBolts. I also have TBolts that don't read the sensor in high resolution mode. I have a couple TBolts with broken temperature sensor chips. Assuming the room temperature is varying several degrees C up and down over the time shown, those plots most closely resemble a TBolt with a blown chip.

Bob

On Sep 10, 2013, at 3:38 PM, Arthur Dent golgarfrincham@yahoo.com wrote:

Hi

Simple way to check it:

Let the temperature in the room move over a 10 C range (open a window …). If the temperature trace does not move the chip isn't doing what it should.

Bob

On Sep 10, 2013, at 5:31 PM, quartz55 quartz55@hughes.net wrote:

Hi

It should be measuring ambient temperature. The GPSDO probably uses it as part of the holdover process. A good blast of room temperature air (heat gun without the heater on) should drop the sensor 5 to 10 degrees.

Bob

On Sep 10, 2013, at 8:43 PM, quartz55 quartz55@hughes.net wrote:

Hi

Ok, you have an unusually well controlled environment in your shack.

The pops are the temperature just barely making it to a 1 C excursion. Think of your temperature as a sort of sine wave. The pops are the peaks of the sine wave.

Bob

On Sep 10, 2013, at 10:02 PM, quartz55 quartz55@hughes.net wrote:

Dave wrote:

I do not know whether LH just displays every
"n-th" sample to produce long-time-scale plots,
or whether it averages "n" samples to get the
displayed value.  If it averages, each pixel
would include data from more than one sample,
which would produce intermediate values that the
GPSDO did not actually report.  You may want to
set the time scale so you can see each one-second
sample (I think one minute per division will do
this).  At that scale, you may find that all of
the samples are in one degree increments.  In
other words, the appearance of intermediate
values may be an artifact of display averaging --
the actual data from the GPSDO may be strictly in
1v increments.  Mark could say for sure.

We (the time-nuts community) do not have hard
data about how the temperature data is used in
the Trimble GPSDOs, but it appears that it is not
used during locked operation except to "teach"
the unit about the OCXO's temperature
coefficient.  What it has "learned" is applied
during holdover in an attempt to improve holdover
stability.  I doubt many time nuts would make
critical measurements while their GPSDO was
unlocked, so there is probably no practical
difference as far as we are concerned.

Best regards,

Charles

I am tempted to use the monty python exhortation "Start again"

If I am reading your screen shots correctly the 01:51:57 UTC shot is before the antenna move and the 14:02:03 one after the move.
HOWEVER, both shots show the same saved position. That is certainly not going to be optimal. You should let it survey again.

Mike

Le 11 sept. 2013 à 16:17, quartz55 a écrit :

I can testify to Warren's comments. I've got an Adafruit Breakout Board that I hook up to my computer from time to time, and it marches all around the neighborhood on the map looking for my house.  =)  Eventually my timing antenna will go up in the attic, just under the peak.

Bob - AE6RV

Hi

Ideally you would like the position error to be under 10" for the device to work at it's best. That's probably going to equate to a couple of inches of error in X, Y, and Z.  Since GPS has cyclical errors, you need an average over a few days to get to that level.

Bob

On Sep 11, 2013, at 1:49 PM, quartz55 quartz55@hughes.net wrote:

Hi

As you do these surveys, write down the results. You probably will do several surveys on each antenna location before you are done. Looking at the variation between the results will give you an idea of what's going on.

Bob

On Sep 11, 2013, at 9:48 PM, quartz55 quartz55@hughes.net wrote:

Hi

Looks like RG-6 Quad Shield is about $50 for a 500' spool at the local big box stores.

Bob

On Sep 12, 2013, at 10:10 AM, quartz55 quartz55@hughes.net wrote:

Hi

Unless you have it shipped in, that's pretty much the situation everywhere. I have several lifetime supply spools of this and that. Some of them I bought new. Others I picked up at garage sales, still with a lifetime supply of cable on the spool. Oddly enough some were replacements for other "lifetime" supplies that got used up….

Bob

On Sep 12, 2013, at 9:50 PM, quartz55 quartz55@hughes.net wrote:

Hi

On Sep 14, 2013, at 12:45 PM, "quartz55" quartz55@hughes.net wrote:

As long as the GPS antenna does not rotate that should be a good location. If it rotates, you will get a few inches of displacement which is less than ideal. The larger issue will be how the antenna handles lightning and the near field transmit power from the beams.

PPT = parts per trillion that's one in 1,000,000,000,000 (12 zeros). One Hz at 10 MHz is 0.1 PPM. PPM is 1 in 1,000,000 (six zeros). PPB is nine zeros, or one Hz at 1 GHz. It's also one nanosecond per second.

300 ppt would be 0.3 Hz at one GHz.

(yes, you can find a lot) of posts to the list where I've slipped a decimal on that stuff).

Also include the errors in the GPS signal:

1. Uncorrected ionospheric errors
2. GPS clock errors
3. GPS almanac errors
4. Antenna location errors (including interesting trivia like tides)
5. Multi path signal errors
6. Temperature induced errors (or not) on the antenna
7. Drift / phase errors in the GPS receiver (there's lots of doppler on the signals).
8. Just plain dumb decisions by the firmware

Since most of the GPS errors are going to "track out" they will not show up on the display. They will indeed shift your output frequency.

The temperature stability of those OCXO's likely is within about 2:1. Aging wise they are like any OCXO, the longer they are kept power on, the less they will drift.

Bob

Hi

As long as the wind does not blow the tower around, that's probably your best location.

Bob

On Sep 14, 2013, at 1:26 PM, "quartz55" quartz55@hughes.net wrote:

Note "300 ppt" is a "fractional frequency", unit-less value, so
at 10 MHz, 300e-12 * 1e7 Hz =  0.003 Hz
at 1 GHz, 300e-12 * 1e9 Hz = 0.3 Hz

Yes and no; it's a complicated subject. For now, just two points:

A measure of frequency implies some measurement duration. A given TBolt may be off by more than 1e-11 in frequency over seconds or minutes even though if you measure over a day it is accurate to less than 1e-13. This is one problem with interpreting the "OSC" value.

A second problem is that a TBolt can't really know its own accuracy; that requires an external frequency reference, so take the PPS and OSC with a grain of salt. However, in general, the TBolt will steer its 10 MHz oscillator so as to minimize the PPS and OSC values. As such they can be used as a rough idea of how well the unit is performing.

/tvb

Hi

If you mostly keep the beams pointed into the wind, I'd do that before you do the next survey.

Bob

On Sep 14, 2013, at 2:59 PM, "quartz55" quartz55@hughes.net wrote:

OT for the current heading, so I renamed it "Oscillator stability"

as Tom says, "it's a complicated subject".
And to complicate things even further, here are a few of advanced subtleties
that I've observed from the TBolt when using LadyHeather.

1. The TBolt uses the received GPS signal as the reference for the
   calculated OSC freq offset and the Phase offset, over a measurement time of
   1 sec.
   Unfortunately, from second to second the GPS signal is very noisy.
   Fortunately, LadyHeather can display plots of the data with several helpful
   user options, such as gain, offset, and most important length of time
   averaged.

2. The Osc freq display plot of LH is so noisy that I find it mostly
   useless,
   unless I turn on LH's display filter to average the data over more than 1
   second.
   LH allows you to manually turn-on and set the display filter to any time
   period desired,
   doing so this will greatly reduce the noise of the Osc plot.
   (10 samples is the display filter default, but I find 100sec to be a better
   place to start, for most things)
   A problem with the LH Osc freq plot even after filtering, is that the
   frequency difference data can not be counted on to be more accurate than a
   few parts in 1e-12 due to some offset rounding problems that often occurs.

3. On the other hand, the filtered Phase plot has no known offset error.
   The Tbolt accurately shows time/phase different between the 1PPS and the
   received GPS signal,
   and when disciplined, it assumes if there is a difference, then the GPS is
   always right.
   This is why the antenna placement and setup is so important. Gunk in, Gunk
   out.

4. The GPS signal, even on a 'perfect antenna', tends to wonders around ~10
   ns PP independently of the time period averaged.
   So if LH is showing less than ~ 10 ns of GPS noise in the phase plot,
   it is because the control loop is set too fast and therefore forcing the
   Osc's freq to change a little so that it's phase will wonder around with the
   GPS's noise.
   Tbolt's max useable time constant is only 1000 sec, which is not nearly long
   enough to avoid this problem, when using a stable external osc like a good
   RB.
   To avoid tracking the noisy GPS data, the extended TC method must be used to
   set the Tbolt's osc to values >> 1000 seconds,
   and/or you can reduce the speed of  the phase tracking using the damping
   setting..

5. How well and how fast the Tbolt minimizes the PPS phase and freq offset
   compared to the received GPS signal all depends on tuning.
   The Tbolt's TC determines what the Frequency  tracking time constant will
   be, and the TBolt's damping setting determines what the Phase tracking time
   multiplier is.
   If you set the damping factor to a large value like 100, then the Phase
   tracking will pretty much be turned off,
   making the disciplined loop more of a freq lock loop instead of a phase lock
   loop. This is done by lowering the gain of the loop's PID integrator.
   This is a way to set the phase's tracking time constant to be much slower
   than the freq TC setting, and if desired the phase tracking TC can be made
   several days long.
   Turning off the phase tracking has it's own set of pros and cons, but in
   most cases it is generally not desirerable in GPSDO.
   A damping setting of 0.7 to 1 will give the best overall compromise between
   the trade-off of not adding extra freq noise but still allowing good phase
   tracking.

6. What some do not realize is to correct for any phase drift error, the
   Oscillator must be set off frequency.
   When the frequency is correct there is no further change in the present
   phase, whatever the present phase may be or wherever it may of come from.
   The faster you want to correct or change the present phase difference, no
   mater how it got there, the larger that the present frequency error must be
   made. (this causes freq noise)
   The trade off is, if you do not correct the present phase error then the
   past average frequency will be in error.

7. So it is all a matter of what is more important to the application,
   present frequency error and noise or the average of all past frequency
   errors?
   The goal of most GPSDO is to keep the average past frequency error to zero.
   (a Phase Lock Loop)
   Where as for many transmitter things such as used by Hams,  it is the
   present errors and noise that is more important.
   So no need to cause a present freq error just to fix something that happened
   in the past.
   The past is gone and what happened before does not matter anymore. (a Freq
   Lock Loop)

ws

----- Original Message -----
From: "Tom Van Baak"
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Subject: Re: [time-nuts] New NTBW50AA

Note "300 ppt" is a "fractional frequency", unit-less value, so
at 10 MHz, 300e-12 * 1e7 Hz =  0.003 Hz
at 1 GHz, 300e-12 * 1e9 Hz = 0.3 Hz

Yes and no; it's a complicated subject. For now, just two points:

A measure of frequency implies some measurement duration. A given TBolt may
be off by more than 1e-11 in frequency over seconds or minutes even though
if you measure over a day it is accurate to less than 1e-13. This is one
problem with interpreting the "OSC" value.

A second problem is that a TBolt can't really know its own accuracy; that
requires an external frequency reference, so take the PPS and OSC with a
grain of salt. However, in general, the TBolt will steer its 10 MHz
oscillator so as to minimize the PPS and OSC values. As such they can be
used as a rough idea of how well the unit is performing.

/tvb

Hi Warren,

There's a lot of good information in this post, and I've discovered a lot of it while writing my GPSDO PLL.  In point 5, you mention that to correct for frequency it has to be off frequency.  I've seen this on both sides of it.  From time to time, I see extremely long periods of no DAC activity.  And at other times, it's moving back and forth; apparently because the DAC is about 1 bit too small.  In my PLL, I've just decided to accept the phase oscillation when it happens and blame it on two main factors.  One is the size in bits of the DAC, about which there's little I can do.  (Well, Jacques Audet came up with something to get one more bit out of it.) 

The other is the Oncore sawtooth, which I'll start working on sometime this week.  The idea of keeping the phase a bit off from the PPS is just a bit too much to bother with for me, I think.  All I have to work with is an 18F2220 PIC running at 40MHz, and I'd like to keep it as simple as possible.  It's already a lot more accurate than I had expected to be able to get.  And it's not like the slope detector on this thing is all that reliable down in the single digit nanoseconds.

Sorry for the thread steal.  Thanks for the review.

Bob - AE6RV

So, what settings would you recommend for an application where frequency
accuracy and low phase noise of the 10 MHz output are the objectives?

In particular, I'm not sure I understand how to establish the "extended
TC method."

Thanks!
Jim
wb4gcs@amsat.org

On 9/14/2013 6:21 PM, WarrenS wrote:

Hi

The OCXO in the TBolt is quite low phase noise as a stand alone oscillator, It's not all that spur free in the TBolt. There's not a lot you can do about that with any settings. The OCXO in the NTBW50AA (and similar) is not as lot phase noise as the TBolt. It's also got issues "as installed". The whole settings thing does not apply to the NTBW50's since you can't change the loop settings on them with LH.

Bob

On Sep 15, 2013, at 7:14 AM, Jim Sanford wb4gcs@wb4gcs.org wrote:

Hi

Should drink coffee first and then type messages..

On Sep 15, 2013, at 9:12 AM, Bob Camp lists@rtty.us wrote:

how about LOW phase noise

Your best bet for low phase noise at microwaves is still to lock up a 100 MHz VCXO and don't sweat the noise & spurs at lower frequencies.

Bob

It seems to me that you're fixing a problem that doesn't exist.  Have you tried just putting it somewhere convenient and leaving it alone to see what happens?

Bob - AE6RV

Dave wrote:

The height of the antenna above average terrain doesn't mean a lot
with satellite signals.  What you need is a clear view of the sky
above 10 or 15 degrees elevation for as much of the azimuth as you
can arrange (and particularly the southern hemisphere of sky).  So,
for example, if you have a "high spot" on the property that is
covered with trees that you can't get above with your GPS antenna,
and a lower spot with a clear sky view, the lower spot is better for
a GPS antenna.  A hillside that slopes off to the south can be an
excellent location.  It sounds like somewhere to the south toward or
at the fence line may be your best location.  Use direct-burial coax,
rent a ditch witch for the day, and you're set.  Remember -- it is
clear sky view you are after, NOT height.

A bit of height above the nearby ground can help with
multipath.  Survey-grade choke-ring antennas are better about this by
design.  Some folks use a metal "ground plane" under the GPS antenna
(it is not really operating as a ground plane, rather, it is simply
shielding the antenna from low-incidence signals).  If the antenna is
at least 10 feet above the nearby ground and your elevation mask is
set to 15 degrees or more, you shouldn't have multipath problems
serious enough to degrade GPS timing (i.e., other errors will
dominate).  Note that the elevation mask can't reject the multipath
itself -- it doesn't steer the antenna sensitivity -- but low
satellites are the ones that suffer the most multipath unless you are
in an "urban canyon" or have other strong L-band reflectors nearby,
so by excluding low satellites you also exclude the multipath.  Since
low satellites also suffer the worst atmospheric variability,
excluding them generally tightens up the timing solution also.

Best regards,

Charles

Dave wrote:

It's not just the height of the trees, it's the horizontal distance
from the antenna location to the trees, too -- the elevation angle
above the antenna location (elevation = arctan (tree height/distance
to trees) (in this case, "tree height" means height of the trees
above the horizontal plane of the antenna, so it includes any
difference in the ground height at the tree location, as well).

At the end of the day, you want the most open sky you can get,
particularly the southern hemisphere of sky, but the lowest
elevations (say, under 20 degrees elevation) are not nearly as
important as 20 through 90 degrees.

Best regards,

Charles

Lee, if I can make a couple of comments, first, you can have large
voltage differences among your 23 "ground" rods, depending on the ground
terminus of the lightning strokes. Second, antennae and feed lines that
do not attract lightning due to being "hidden" can still be subject to
large induced voltages.
I'd suggest all the ground rods and antenna bases be connected directly
with large cable so they are all truly at the same ground potential...
Don

Lee Mushel

--
“The power of accurate observation is commonly called cynicism by those
who have not got it.”
-George Bernard Shaw

Dr. Don Latham AJ7LL
Six Mile Systems LLC
17850 Six Mile Road
POB 134
Huson, MT, 59846
VOX 406-626-4304
Skype: buffler2
www.lightningforensics.com
www.sixmilesystems.com

Lightning is certainly one of Old Mother Nature's principal weapons as well
as being extremely unpredictable.  My House/Shack is on the side of a hill
with the Antenna Farm on top of the hill about 120 yds away with an
additional 30 ft. of elevation.  There is a metal "lightning rod" extending
high enough to provide a "cone of protection" for the house and is grounded
directly.  And there are five other metal antennas on that roof, two to a
separate ground and three to still another which is close to the shack
"ground field" which is three additional  ground rods.  All ground rods I
mention are the standard 8 ft. copper plated steel items.  Each of five
antennas in the antenna field also have individual ground rods and I guess
if you follow the cable shields you could say that they are all connected
together.    A couple of years ago I counted all ground rods and came up
with 23.  Before all of the metal was added and the "lightning rod" was the
only metal extending about 20 ft. above the roof and we had an electrical
storm my wife would complain that she could feel her hair trying to rise in
response to the field coming from the cable which ran across the roof and at
it's closest point was only 6-7 ft. from her head as the crow flies.  But
after all the additional metal was added in the form of antennas with
grounds  she no longer complained.

I do not claim to understand what goes on around here at an elevation of
about 102 ft. above the valley floor but I believe that we have been
"fortunate"  (or lucky if you prefer that word) and we have so much metal in
the air that most "discharges" are not of the type that is accompanied by
thunder!  Two years ago we had a tree die that was no more than 30 ft. from
the house.  Since I have not always been able to accurately predict where
trees will fall that I cut myself I hired a professional to take it down and
he took one look at it, reached up and stripped off a piece of bark and
commented, "See those lines?  This tree was struck by lightning.  That's
what killed it!"  But no lightning related damage to structure or equipment
here for nearly 15 years!

My only thought on the subject was that only a fool would fail to disconnect
an antenna that rises above the house roof  during an electrical storm.  I
freely admit that I have several ham radio VHF antennas  (and a GPS antenna
supplying the disciplined system for frequency reference) well below roof
peak level  (clear view to south for GPS, of course) that I do not
disconnect from inexpensive radios maintained for the purpose.

This is risk I accept.  And I certainly have seen paths followed by
lightning that are truly amazing!  ....and horrendously damaging.  Never
forget that you only live once and you do have a perfect right to enjoy your
hobby without fear.

Regards,

Lee A. Mushel  K9WRU

----- Original Message -----
From: "quartz55" quartz55@hughes.net
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Sunday, September 15, 2013 12:13 PM
Subject: Re: [time-nuts] New NTBW50AA

.  I'm not thrilled having it above the beams, it's the highest metal thing
in the area and most likely more prone to lightning than anything else
excpet the trees and it will blow around a bit up there as well as rotating
once in a while.  I did have a strike here once, but it was down by the barn
and was looking for the underground telephone cables, it blew apart a post
and knocked off the boards, it was maybe 100 yards from the shack.  It
wouldn't be much of a problem to dig a tiny trench to the fence and I may
try that after this precise survey is done, then do another and see if
anything changes.  I could hide it i

Don,

Thanks for the suggestion!  I have no doubt that you are correct and
especially so at the moment of any "strike" or discharge.  But these rods
cover an area approximately 200 by 500 ft. and I don't find heavy cable
"practical!"  Feedline varies from the RG-58 you would expect to 7/8 inch
Andrew (350').

Lee
----- Original Message -----
From: "Don Latham" djl@montana.com
To: "Discussion of precise time and frequency measurement"
time-nuts@febo.com
Sent: Sunday, September 15, 2013 3:54 PM
Subject: Re: [time-nuts] New NTBW50AA