csteinm...@yandex.com said:
> The fact that one thing is phase-locked to another does not necessarily
> mean it puts out a good, clean signal. At short time scales (tau less than
> ~100 seconds), the PPS signal from any GPS receiver is noisy. At tau =
> 1second, it is shockingly noisy
kb...@n1k.org said:
> The bigger problem for NTP is when the leap second correction process is
> thrown off by the âtime warpâ. When leap seconds get fixed in mid-August
> rather than the end of June ⦠not a good thing.
Is that still a problem? If so, do you have any details. I don't
hol...@hotmail.com said:
> Happy until the next power glitch... the setting does not seem to persist
> between boots. There may also be other conditions that causes it to forget
> your date.
I just power cycled mine. It came back correct without setting the date.
I've assumed there is a
petervince1...@gmail.com said:
> Can I just ask why the Z3801As are having week roll-over problems now - I
> didn't think it was 2048 weeks since GPS "zero-hour" until late on the 6th
> of April 2019?
It's probably 1024 weeks since a date was built into the firmware.
It's like the year 2000
I had one that screwed up. I power cycled and set the date. It's happy now.
I'm not sure of the exact recipe to tell it the right date. After feeding it
a date of roughly today, the status screen jumped to Jan 2007. After it
found a few satellites and such, it jumped to Sep 2016.
--
rich...@karlquist.com said:
> I thought I would check the brain trust here to see if anyone has seen a
> hobbyist grade temperature testing chamber or kit or homebrew design. I
> have some crystals, oscillators, and other electronics I would like to
> characterize over temperature. I know this
glennmaill...@bellsouth.net said:
> Is there a fix for the rollover problem for this instrument short of
> replacing the receiver? In searching the archives, this is the only
> solution that I see.
Sometimes, you can patch the downstream code to work around the bug. It's
only a few lines of
hol...@hotmail.com said:
> I did a little math on the dates and it looks like the rollover happened in
> the last couple of days...
Thanks for the heads up.
Mine started on Aug 17th
/var/log/ntp/clockstats.20160817:57617 2.033 127.127.26.1
T21997010102300103
8 64 0
That's from ntpd's
billm...@gmail.com said:
> If the conductor also has magnetic properties (e.g. if iron were used) then
> magnetic saturation could be an issue.
Ah... Sorry I wasn't clear. How about
Is skin depth an interesting concept if you are using materials commonly used
for magnetic shielding, for
billm...@gmail.com said:
> Skin depth is probably a good place to start with in roughly estimating the
> thickness needed. In copper at 50 Hz, ...
Is skin depth an appropriate concept for magnetic shielding? Or does it get
messed up by saturation?
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tract...@ihug.co.nz said:
> What is the coupling mechanism giving rise to the 50Hz disturbance?
My guess would be mechanical. Maybe from a nearby transformer.
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att...@kinali.ch said:
> Is there any advantage of using groups.io compared to a traditional
> mailinglist? If not, I would prefer a traditional mailinglist. But maybe I
> am just oldfashioned :-)
The obvious advantage is that there is a professional staff keeping things
running so you don't
kb...@n1k.org said:
> Ok let's toss some numbers into the mix.
> The counter time base one day after calibration is in the 0.5 to 1.5 ppb
> range.
I have two 5334Bs wih opt 010. It's been many years since either was near a
calibration lab.
One is 30 ppb fast, the other is 75 ppb fast. (I
lister...@gmail.com said:
> Connecting the 10 MHz output to the Channel A input (on the 5334B) or the
> frequency input (on the 5370B) and setting 50 Ohm termination and AC signals
> but without any other input or external reference results in a frequency
> that is off by about 0.1-0.2 Hz. Is
bill.i...@pobox.com said:
> Different regions can have different phase behavior. I have only seen West
> Coast plots on this list. When I did some work with this in Minnesota in the
> eighties, the phase variation was only about 6 seconds during a day and zero
> from day to day.
On the west
ziggy9+time-n...@pumpkinbrook.com said:
> It IS possible to hack a âstandardâ SV6 receiver such that it will work in
> the XL-DC...
Did your XL-DC have an actual SV6 in it? I didn't see one in the picture
Rick sent out a few days ago. There was a Trible sticker on a chip so I
suppose the
You could get a low cost GPS unit and compare the PPS from it to the PPS from
your setup with the long cable.
Modern GPS receivers are sensitive enough to work with a poor antenna
(indoors) and don't cost much.
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b...@evoria.net said:
> Earlier this year, with some help, I pulled the dish off of an old DishTV
> antenna on the roof and put a 5V bullet antenna on the mast. I also pulled
> a new cable through by attaching it to the old one. The problem is that I
> was not able to measure the new cable.
hol...@hotmail.com said:
> You might want to try a modern GPS receiver. I have some cheap (< $10-20)
> GPS modules with on board patch antennas that work indoors, sitting on the
> floor of the bottom level of a two story stucco-over-wire mesh house, away
> from windows, surrounded on all
albertson.ch...@gmail.com said:
> Next You want one that will last basically "forever" outdoors. The best
> kind have a plastic radome over a metal base. The base has pipe threads for
> mounting on a standard 3/4" galvanized plumbing pipe. The coax wires goes
> down this pie and never sees the
herb...@13thfloor.at said:
>> Ideally you would like a clear view of the sky from
>> about NE clear around to NW (270 degrees).
> That would opt for the balcony, as it faces north and extends the slanted
> roof, so basically clear view from NE to NW down to the horizon.
You are thinking the
ron...@sbcglobal.net said:
> I'm working on NTP and have no idea what's happening. The description says
> it takes over the PC clock, excluding other apps.
It doesn't make sense to have more than one program trying to adjust the
clock. They will just confuse each other.
I think what that is
rick.jon...@hpe.com said:
> HalM was kind enough to come over the other day with some antennae which we
> tried without success.
I was going to suggest taking the cover off and looking inside but it fell
off my to-do list.
GPS receivers are reasonably specialized. I doubt it anybody makes
david-tay...@blueyonder.co.uk said:
> Some notes on using PPS with Windows may be gleaned here. Although the
> device mentioned is no longer available, the general principles will apply.
> http://www.satsignal.eu/ntp/Sure-GPS.htm
It's available via eBay.
SKG16A Bluetooth/RS232/USB UART GPS
davidwh...@gmail.com said:
> I always thought they should bring the varactor or EFC ground out as a
> separate pin but I assume that since they do not, ground noise at least
> within the oscillator does not limit performance.
I'm pretty sure I've seen comments, probably on this list, about
glennmaill...@bellsouth.net said:
> In navigation we used the earth rate of 15.04 degrees per hour. This was
> treated as a 'constant' even though it varied with wind, waves on the ocean
> and other things affecting the instantaneous rotational speed of the earth.
Were the wind and waves and
david-tay...@blueyonder.co.uk said:
> From your data and my own measurements, I feel that using the serial NMEA
> stream would, today, be a last resort, as an Internet sync would be
> considerably better. Would you agree with that?
Depends on your internet connection and/or the specific GPS
t...@radio.sent.com said:
> As I pointed out, what's the difference between an inertial body moving in a
> straight line and a rotating body?
The rotating body has a natural unit of time so there is a convenient way to
make Q dimensionless.
For linear motion, the natural unit of decay would be
It was setup to only send GPRMC sentences.
http://users.megapathdsl.net/~hmurray/time-nuts/RMC-hist.png
Here is what it looks like over time:
http://users.megapathdsl.net/~hmurray/time-nuts/RMC-offset.png
There are interesting glitches at 3 hours and 23 hours. Anybody have any
ideas about
t...@radio.sent.com said:
> So loss effects frequency in one situation and amplitude in the other. How
> can Q relate to both situations?
It's energy loss in both cases.
Is there a term other than Q that is used to describe the rate of energy loss
for things that aren't oscillators?
--
hol...@hotmail.com said:
> A couple of people have asked about the poor message arrival time
> performance of the popular Adafruit Ultimate GPS receiver. I modified
> Lady Heather to analyze the message arrival times using a histogram
> instead of a simple average. When I looked at the
t...@leapsecond.com said:
> Just in case we have some newcomers to the thread I'd like to point out
> that this recent series of measurements of RS232 / NMEA have no bearing at
> all on the quality of the timing output. Timing NMEA is more of a
> curiosity; something to measure at the hundreds or
hol...@hotmail.com said:
> te a histogram of the values (along with the average and standard
> deviation). I'm now using the peak histogram bin(s) to determine the
> message offset time. The histogram technique has the advantage of ignoring
> outlier points that can be caused by the system
> So, you have plotted offset versus temp? Can we see that?
I don't have offset vs temperature. This is what I work with:
http://users.megapathdsl.net/~hmurray/time-nuts/LAN-clock.png
http://users.megapathdsl.net/~hmurray/time-nuts/LAN-temp.png
Scan the wiki page for PID controllers:
g...@rellim.com said:
>> The systems collecting the data have 200-300 microsec peak-peak of
>> clock offset, mostly tracking daily temperature swings.
> How do you know that?
Which "that"?
I don't have a formal proof, just a collection of data that all fits together.
You can get the clock
http://users.megapathdsl.net/~hmurray/time-nuts/T2-hist.png
24K samples from KS-24361
200K samples from Z3801A
The systems collecting the data have 200-300 microsec peak-peak of clock
offset, mostly tracking daily temperature swings.
A major fraction of the timing difference is explained by
mi...@flatsurface.com said:
> Why 6/1 and 12/1? Leap seconds can happen any month. June and December are
> only a preference.
Yes, but it's a very strong preference. My reading is that they will use Jun
and Dec as long as they can keep within a second.
Are there any interesting estimates on
att...@kinali.ch said:
> I am not sure you can apply this definition of Q onto earth. Q is defined
> for harmonic oscillators (or oscillators that can be approximated by an
> harmonic oscillator) but the earth isn't oscillating, it's rotating. While,
> for time keeping purposes, similar in
hol...@hotmail.com said:
> I originally thought the SCPI receivers would be right on time due to
> my original measurements of their message jitter, but when I started
> measureing the actual message arrival times... surprise, surprise, surprise!
> I think the issue is due to the fact that they
hol...@hotmail.com said:
> Here are the results of measuring the difference between the time code in a
> GPS receiver time message and the arrival time of the last byte of the
> message. Negative values mean that the receiver sends the timing message
> after the 1PPS pulse that it describes. The
kb...@n1k.org said:
> If you go back far enough in time â¦. there is another alternative:
>Big rectifier bank, turning AC into DC, often off of multiple phases
> or sources.
>Big DC motor running into a fairly large flywheel.
>AC generator (or in some cases DC
> 24 bit DAC
Which chip are you using? How many useful bits do you think you will get?
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t...@leapsecond.com said:
> Earth is a very noisy, wandering, drifting, incredibly-expensive-to-measure,
> low-precision (though high-Q) clock.
What is the Q of the Earth? It might be on one of your web pages, but I
don't remember seeing it. Google found a few mentions, but I didn't find a
att...@kinali.ch said:
> You can already get 24bit DAC's off the shelf from TI (DAC1282). I do not
> know how stable they are in reality. ...
There are 2 markets for DACs and ADCs. I'll call them DC and RF, but the RF
goes down to audio.
In the DC market, the data sheet talks about linearity
rich...@karlquist.com said:
> That's what we tried to do with the E1938A. A multiplying DAC is used based
> on a reference that is ovenized instead the crystal oven. That certainly
> eliminated the tempco issue with the reference, but then we discovered 1/f
> noise on the reference. We had to
rich...@karlquist.com said:
> Also in 1996, phase microsteppers were already legacy technology and didn't
> have a good reputation for spectral purity. Another non-panacea.
What is a phase microstepper and/or how does it compare to a DDS?
(Google gets lots of hits, but they all refer to
noah.ro...@gmail.com said:
> Discovered that my commercial GPS appliances opted to *apply* yesterday's
> pending leap second, which has made for an interesting day.
Could you please say more?
How are you working around it?
Vendor? Model? Can you take the cover off (or peer in through the
g...@rellim.com said:
> Yes, I know the problem being solved. Like today, the leap second being
> broadcast sooner than ntpd expects, so it picks the wrong month.
Do you know of any ntp servers that have picked the wrong month?
g...@rellim.com said:
>> I don't think there is anything in the
hol...@hotmail.com said:
> I get the Z3801A leap pending flag from the #T1 or #T2 time stamp in the
> :PTIM:TCOD? response.
I see it now. Started a bit after an hour UTC into the new day.
57589 4546.033 127.127.26.1 T22016072001154730+0038 64 0
So either I didn't look carefully enough or it
hol...@hotmail.com said:
> The Z3801A has it messed up... it says the leap will occur on 30 Sep 2016
> (73 days). The Z3801A has two different messages that report the leap
> day... both are wrong.
Which messages are you looking at?
There is a
[You sent that to 3 lists that I'm on. I'll reply here.
I think your X axis is off. Your left edge is 1 second and you don't have
data for that. peerstats is every 64 seconds. (unless you mucked with
maxpoll) I'm guessing the software you used is assuming they are every
second. There may
michael.c...@sfr.fr said:
> The relevant NTP leap-seconds-list file can be downloaded with anonymous ftp
> from the pub directory at time.nist.gov. (The leap-seconds-list file is a
> symbolic link to the data file leap-seconds.3676924800 in the same
> directory. )
The NIST servers at that
nsa...@kfu.com said:
> Yes, thatâs true. Given the facilities I have available with the present
> hardware, I donât believe I have much choice. I am not confident that I
> could tell the difference between noise in the phase detection system and
> PPS jitter variations that small. If the PA6H
jim...@earthlink.net said:
> except that virtually every UART in use today has some sort of buffering
> (whether a FIFO or double buffering) between the CPU interface and the bits
> on the wire, which completely desynchronizes the bits on the wire from the
> CPU interface.
The idea was to
> The systems gravitate towards PLL time constants that average it all away.
You are overlooking hanging bridges.
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how...@leadmon.net said:
> I have also run ppstest, and show a pps stream, granted the weird thing is
> it seems like I get two lines of the same output ever second so not sure
> what is up there.
One is clear changing, the other is assert changing.
There should be info in syslog or whereever
how...@leadmon.net said:
> Does anyone have any ideas, or have this all working under Ubuntu 16.04 LTS?
> I would sure love to get my time server back online, as I pretty much have
> everything on the network sync with it..
The PPS stuff on Linux needs some magic setup. You need to run
kb...@n1k.org said:
> Well, if you actually sit down and measure the serial timing on a modern GPS
> module, you will find that it is very consistent. That degrades quickly if
> you enable a few dozen sentences. Sub 10 ms accuracy is not a tough target
> to hit when standing still.
Do you
kb...@n1k.org said:
>If the objective is a time *display* that is read with a human eye,
> anything under 1 ms is not of much use. Your eye canât detect it.
What can your eye detect?
Is there good data? Does it vary with age or things like that?
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albertson.ch...@gmail.com said:
> I don't know what you'd do with 10KHz except divide it by 10,000 to create
> your own 1PPS but how to get it to "tick" on the exact UTC second?
If you are building a PLL, it's a lot easier to filter a 10KHz signal than a
1 Hz signal.
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> I've done NTP before, I wanted to do this with GPS since I have never done
> a GPS implementation before.
You loose your time-nut certification unless you use the PPS.
Most low cost GPS units speak NMEA. It's ascii text so you can debug stuff
with your favorite terminal program. cat works
kb...@n1k.org said:
> All of those motors in the building are rotating at line frequency. You
> donât just have an electromagnetic field. You can have an acoustic /
> vibration field as well. Probably not a big deal, but itâs there â¦.
Most of the medium sized motors run at slightly
t...@patoka.org said:
> In addition, even MCU has not enough resources to handle TCP/IP, DHCP and
> NTP, it is some solutions available to outsource it to dedicated chips. I
> was using WIZ5100 (assembled as a modules) with great success.
NTP is pretty simple. If you are willing to take a
johnswens...@comcast.net said:
> I'm looking into a TU36-D400-020 receiver.
> What antenna to use? I would prefer something mounted inside the case. It
> is wood so an internal antenna will hopefully work. The board comes with a
> pigtail but it is not SMA.
That's an old receiver. Modern
jfitzger...@alum.wpi.edu said:
> What organization is in charge of inserting leap seconds into the Martian
> time scale?
How good is the data on the rotation rate for Mars? Is it good enough so
that they would need leap seconds?
How about leap years/days? (assuming they have a calandar)
--
i...@blackmountainforge.com said:
> There is a company in the USA that manufactures a product called
> BatteryTender - excellent float charger and maintainer. Costco sells them
> for $40
How do those types of chargers work when there is a load?
It's not the typical "float" there is also
b...@evoria.net said:
> So, since I need to power the 5370 (preferably both) I'm looking at a deep
> cycle battery, a charger, and an inverter? At this point in the process, a
> power line monitor is looking like a good solution. At least it would tell
> me to ignore the test results.
Yes, you
b...@evoria.net said:
> So, what to do? I've been looking at UPS devices, and I don't even
> understand enough to waste my money on a bad one.
A UPS has 2 major properties. One is the amount of power it can put out.
The other is the battery size which translates into how long it will last.
rch...@earthlink.net said:
> âLongitude: The True Story of a Lone Genius Who Solved the Greatest
> Scientific Problem of His Time,â by Dava Sobel (Author).
There is also a coffee table version with lots of good pictures.
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jim...@earthlink.net said:
> I'm fine with writing the SCPI commands and parsing the output, I'm just
> looking for the "glue" between "send_message_to_instrument" or
> "read_message_from_instrument" and the instrument itself.
Why do you need any glue? What type of device is it? Why not just
kb...@n1k.org said:
> There is also the somewhat non-intuitive need to stick a low value resistor
> in the base. Done properly, they are very reproducible and reasonably
> insensitive to load.
Is that required for real circuits or just for the simulations?
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bro...@pacific.net said:
> At one point they were looking into making a GPS time receiver where the
> cable length calibration would be built-in.
How would you do that?
The obvious way is to compare the time you get with a known-good time, but if
you had that, why would you want this new GPS
p...@heypete.com said:
> I have seen those, but I have little experience with PICs and the Wife
> Acceptance Factor of buying more stuff for a one-off measurement is low.
The PIC family is very similar to AVRs. The picPET and friends are 8 pin
DIPs so the Wife is unlikely to notice the
d...@irtelemetrics.com said:
> I'm looking for a quick and dirty algorithm or method to generate a pulse
> train at arbitrary frequencies based on a fixed clock source. This will be
> run as code in a timer ISR in a microcontroller, so some
Google for DDS.
The hardware implementation is
dan...@verizon.net said:
> Maybe, but simply by adjusting mine by measuring the 32 kHz output with an
> accurate counter I can get them to keep to within about one second a month.
What did you adjust? I assume it's software.
How well do typical VCO adjustments work with tuning forks?
My
t...@patoka.org said:
> For very long time, may be Main Frequency (60 Hz) could be utilised. Say,
> MCU could count and compare Zero-Crossings and impulses from DS32xx chips.
> After several days, you'll see where it goes.
Power in Silicon Valley isn't stable enough to make that approach
I assume you are doing this for fun. That means you get to do whatever you
think will be fun.
The DS3231 is pretty crappy by time nuts standards. If you can also measure
the temperature, you should be able to make neat graphs. If you watch it as
the temperature ramps up slowly, you should
> The highest Q I remember seeing were BVA's that reached 2e6 to 3e6 @ 5MHz
What determines the Q of a crystal? Is it atomic level impurities? Crystal
defects? ...
How has that changed over time? Is there a Moore's law for crystals?
How does the quality of crystals used for timing compare
stev...@suddenlink.net said:
> The phrase "over-determined clock solution" is used in the Trimble
> Thunderbolt user manual in describing operation of the Thunderbolt GPS
> receiver.
> What does "over-determined clock solution" mean?
You are trying to solve for X, Y, Z, and T. (or the polar
> Also how many hobbyists are going to have reels of parts?
Reels of small resistors or caps are ballpark of $20. I'd be happy to buy
one for any part that is likely to get use multiple times on a board and
again on the next board.
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kb...@n1k.org said:
> Iâve been doing SMT assembly for 40 years. I have never ever seen anybody
> with a process that âjust workedâ. They all involve some amount of fine
> tuning and design optimization.
As an example... I remember supplying dead chips to the fab house so they
could
t...@electrictime.com said:
> In the suburb of Boston where we are located - you never have to correct an
> electrical clock between the daylight saving time changes. This of course
> assumes you haven't lost power - due to major snow storms etc
I agree with the spirit of your comment, but
g...@rellim.com said:
> While you are waiting check out the attached scatter plot. Now THAT is a
> good $25 GPS! Beats the heck outta any Garmin. CEP(95) of 1.5 meters over
> 1,000 seconds.
What type of GPS was that?
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> The ATTinys have brownout detectors in them thatâs supposed to keep them
> from going bonkers during undervolt periods.
Startup and/or brownout has long been a nasty problem area for digital
designers.
In the old old days, there was typically a R/C delay on the reset pin to a
CPU. That
att...@kinali.ch said:
> Temperature, in an office or lab, does not change that much to cause large
> differences.
Maybe in your lab.
I'd expect that will change as people get more sensitive to energy costs.
Things like turning down/off the heat/cooling at night can lead to large
swings.
In general, if you have a mysterious GPS thing, especially high volume
consumer gear, gpsd is a very good place to start. They are focused on
position but it puts time into shared memory where ntpd can get it.
> generic operation under Linux (Ubuntu)
gpsd is developed on Linux. It works on
bruce.griffi...@xtra.co.nz said:
> More likely the missing GPS receiver board is installed over the ground
> plane.
There is a small metal shield in the upper right with some coax coming out of
it. It says FURUNO. They make GPS stuff.
Google finds:
david-tay...@blueyonder.co.uk said:
> I think that all the GPS devices I've used sent the time /after/ the PPS
> pulse. I've never met one which sent it before.
That makes sense for NMEA format messages which have fractional seconds in
some of the message formats. Mostly they are 0, but if
hol...@hotmail.com said:
> The receiver is reporting the correct UTC offset and appears to be working
> properly... it's just that the time is one second off from what 7 other
> models of receivers are reporting...
I'm pretty sure that I've seen one GPS unit that was off by a second. I'm
bruce.griffi...@xtra.co.nz said:
> All the filtering and down mixing is done in the digital domain.
> Anitialiasing filters in front of the ADCs are also be required.
What sort of bandwidth is expected?
The usual trick with audio ADCs is to have a low cost analog filter that
does't have a
kb...@n1k.org said:
> The glitches are to narrow (short duration) and far to regular for the
> ionosphere to be the issue.
Is multipath from a large airliner in a landing pattern likely to cause that
sort of problems?
I'm 20+ miles off the end of SFO, but it's common to see large planes
bneu...@t-online.de said:
> Hello Fellow time-nuts, I am looking for a simple solution to discipline my
> 10 MHz reference OCXO in my private lab with an 1 PPS signal from a separate
> GPS receiver. I am curious if there is a solution possible without
> programming a microcontroller, as I am an
How GPS Found Its Way
08:36 minutes, Brad Parkinson
http://www.sciencefriday.com/segments/how-gps-found-its-way/
Marconi prize
Stanford Professor Bradford Parkinson, Father of GPS, to Receive the 2016
Marconi Prize
preilley_...@comcast.net said:
> I have a question. I, of small brain, am wondering: if the time
> difference between the top of the mountain and the bottom of the mountain is
> 20 nS over 24 hours could you repeat the same experiment using GPS?The
> time difference of 20 nS is measurable
mag...@rubidium.dyndns.org said:
> Friday was spectacular, as we where a few lucky to be bussed out the LIGO
> detector, Livingston. Extremely fascinating hardware. It's essentially a
> Michelson interferometer with 4 km arms. When you are there you only see
> half of it, as the building
catg...@bordernet.com.au said:
> What I am trying to understand is, what does it REALLY mean when the
> manufacturer's specs for a frequency standard or 'clock' claim a certain
> accuracy. For ease and argument's sake let us assume that the accuracy is
> given as 100 ppm or 1e-4
...
> But
jim...@earthlink.net said:
> Well, in deep space optical comm, we send many photons with a laser, and we
> use pulse position modulation at the receiver detecting single photons (or
> "few photons"), by which we can send "many bits/photon" (e.g. if you have
> 256 possible time slots in which
t...@leapsecond.com said:
> Any of these methods is going to be a challenge, given their 500 ps
> requirement and their $2k budget.
How stable are surplus rubidium oscillators?
How close could you get if you brought two of them together, compared phase,
drove them to the site for a nights
att...@kinali.ch said:
> The limit for TDCs in FPGAs seems to be around 5-20ps RMS (which makes it
> more like 15-50ps in "real" precision) depending on type and technology.
> Going down to below 20ps usually means to take the latest tech FPGA with
> lots of redundant structures, which makes the
> What was the reason for holdover?
Crappy antenna location.
> What puzzles me is the large hump upwards in DACvalue. Anyone knows what is
> the reason?
My guess is poor filtering on the initial data when coming out of holdover,
probably complicated by inadequate testing and/or that case
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