Re: Clarifications about PPS SHM content

[Gary E. Miller]

Yo Martin!

On Wed, 25 Mar 2020 02:31:29 -0400
Martin Boissonneault <address@hidden> wrote:

> >> I have a Nooelec NESDR SMArtee for comparison, and the LNA does
> >> help me pull in more planes.  
> > I see 300 miles do I really better?  
> 
> I envy your reception! I currently cannot do better as I have no way
> to cable the antennas to the outside.

My Antenna is on a mast, on my house roof, on butte.

> The inboard LNA benefits the
> common indoors mini-antenna hooked by a few feets of thin cable.

GHz signals do not pass walls or windows well.

> Do you feed ADSBexchange <https://www.adsbexchange.com/> and OpenSky 
> network <https://opensky-network.org/>?

I feed FlightRadar24, in return for a free business account.  They
have good coverage in my area.  The adsbx looks so-so, and the opensky
not good at all.  Any way to see where their feeders are?

> I wonder if you feed UAT 978MHz?

Yes.

> > At a GHz you want the ground plane directly the antenna.  
> 
> ROTFL!!! No, my ground is not a small bag of dirt attached to the 
> grounding wire ;-) The antennas are a few feet from the receivers,
> with a ground plane (cover from my old washing machine).

Too big.  A 1 GHz a ground plane begger than about 60cm is sub-optimal.

u-blox has some good white papers on the subject.

> > I'd like to see real data to prove that.  
> 
> See /initial_turbo/ there: Overclocking options in config.txt 
> <https://www.raspberrypi.org/documentation/configuration/config-txt/overclocking.md>
>  
> and the thread 
> <https://www.raspberrypi.org/forums/viewtopic.php?f=29&t=6201&start=425#p180099>
>  
> linked.

I asked for data, not guesses.

> I do use /initial_turbo=60/, so the maximum speed is used until 60 
> seconds or until /cpufreq/ sets a frequency, which will be done by
> the performance governor in my configuration (Right?).

Don't ask me, look at what your system tells you.  Data, not anecdotes.

> but it makes
> sense to have the CPU use the same governor all the time instead of
> possibly hopping from one speed to another on time servers.

ALL governors change the CPU speeds.  Only how much and when is different.

> > The RasPi overheats at the drop of a hat.  Very rare to keep one
> > running at full speed.  
> 
> I put small heatsinks 
> <https://www.buyapi.ca/product/aluminum-heatsink-for-raspberry-pi-b2-2-pack/> 
> on and it doesn't usually overheat. My recorded stats show a handful
> of potential overheats, which where probably when I recompiled the
> kernel.

"usually"?  I feel so much better now.  :-)

> I'm confused:
> sudo cat /sys/devices/system/cpu/cpu0/cpufreq/cpuinfo_cur_freq
> 600000
> cat /sys/devices/system/cpu/cpu0/cpufreq/scaling_cur_freq
> 1400000
> So, the frequency is scaling from 600MHz to 1.4GHz? What does that do
> to NTPd???

Not much is you are using KPPS.

> Well, some like the DS3231 are pretty good as they use a TCXO, they 
> apply a capacitive correction factor to the oscillator depending on
> the ambient temps. The frequency precision on that one is from
> 2.0ppm to 3.5ppm without any calibration.

And you confirmed that how?  Or you believed the amrketing?

> According to /timedatectl/, my system clock and RTC are in sync and
> kept in sync. That's all I care about, my RasPi is always on and the
> RTC is only needed for short periods of time.

Yes, as long as you do not reboot often.

> >> /vm.dirty_expire_centisecs/ to 2.5 minutes,/vm.dirty_ratio = 40/
> >> and /vm.dirty_background_ratio = 30/. Do you think that's
> >> allright?  
> > You tell me.  Did it help or hurt?  
> 
> I/Os are down, but I don't see a significant impact on time.

You should see less frequency jitter.  Not much, but noticeable.

> > And good to verify those setting occasionally.  
> 
> Yes, for some reason I lost my settings in the past because of
> (shuffles excuses card pack and picks one) Cosmic rays ;-)

Common with the u-blox.

> It seems that UBX-CFG-TMODE2 does not work on the MAX-M8Q, the
> message returns a NAK. So, 2D/3D might have some real impact.

Yup.  Not on the M8Q.  No time mode at all.

> > Optimal OXCO temp is pretty high, I seem to remember near 55C?  If
> > your house gets that hot in the summer you have other problems.  
> 
> Of course it doesn't, but it reached and held near 40__C for days. 
> Consequently, the RasPi cooling was less efficient, and it's temps
> shot up above 65__C, with only a piece of paper as a cover. It's
> visible in my graphs between June and October 2019.

Then set your temp at 70C and leave it there all year.

RGDS
GARY
---------------------------------------------------------------------------
Gary E. Miller Rellim 109 NW Wilmington Ave., Suite E, Bend, OR 97703
        address@hidden  Tel:+1 541 382 8588

            Veritas liberabit vos. -- Quid est veritas?
    "If you can't measure it, you can't improve it." - Lord Kelvin

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