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KIWI OSD inserter

  • Porównanie inserterów IOTA VTI oraz KIWI OSD: https://www.youtube.com/watch?v=KyVN-QVOfv0&t=69s
  • You ran your KIWI-OSD off a battery – which is the cleanest source of power –  a noisy power supply, or crackly power or video cables or connectors, or electrically noisy appliances on the same circuit do, or allow,  emit electrical spikes that mimic the 1pps signal, and this tricks the KIWI-OSD (or any VTI for that matter) into thinking that it received extra 1pps signals.
  • Ustawianie jasności napisów – Adjusting the blue trimpot clockwise had the effect of re-introducing some white into the digits when turned up to maximum, as well as darkening the block of shading. That means I can now read the display again, no matter how dark the background is, without having to jump through hoops.
  • In the IOTA-VTI, the ephemeris is regularly updated and compared with the  current display. Whenever a discrepancy is detected, a screen message is  displayed. The number of seconds that it can be in error is small, because  of how a default GPS-UT offset is built into in the GPS receiver. The 2nd version of the VTI was improved by including a battery to ensure the  actual GPS-UTC offset was held between sessions. The KIWI functions quite differently. Once it is powered u p, it only  monitors the occurrence of the seconds marker. It does not monitor whether  the value of the second is being correctly displayed. The only way to  validate the value of the seconds display is to perform a reset. And to be  sure that the KIWI has downloaded a current ephemeris, you must wait 12.5  minutes (or some such similar value). If you don’t do the reset, the Kiwi is  functionally incapable of alerting you to a mismatch between the displayed  time and actual time.

Two important aspects of this. Firstly, if the Kiwi is used regularly (i.e.  at least monthly) the GPS-UTC offset should be retained in the GPS receiver  such that the displayed time is OK from power-up (assuming no leap seconds).  However you have no means of knowing, apart from doing the reset, of whether  or not the receiver had retained the last GPS-UT offset. As a result, the  reset process is essential to ensure integrity in the time base. As for the KIWI updating the almanac, someone reported, maybe Steve Preston, that you had to press the reset button ‘twice’ to get the new almanac time stamps to show correctly on screen. You can certainly test that against your WWV signal and find out if one button push is sufficient, or if you need two button pushes.

  • Every time you push the yellow button in a Kiwi, you have to do it twice – once to see the message (either “Previous times OK” or “Use frame counts”).  That message stays on the screen until you push the button again, at which time the box resets, goes through the process of displaying lat, long, elevation, etc. and then begins timestamping.
    As you soon you see the message “Previous times OK”, your next button push should put the box into the correct status with an updated almanac where you can trust its timestamps.

Here’s how KIWI-OSD works (Dave Gault):

Cały proces opisany jest tu (21 kwiecień 2017): http://www.kuriwaobservatory.com/pdf_files/KIWI-OSD_HowStartUpWorks.pdf

  • BEFORE Power is applied.  KIWI-OSD know nothing about time.  The GPS receiver retains some sort of Almanac that gives the GPS-time to UTC time offset.  It could be the Almanac that was installed at the factory when the receiver was made (in the case of my KIWI-OSD P#1 GPS receiver, that was 2003 or 2004.  It could be the Almanac that was downloaded when it was used last night.  Who knows…?
  • Power is applied and a GPS-fix is obtained.  The GPS outputs the 1pps signal.  KIWI monitors the 1pps for about 10 seconds during the startup sequence and adjust it’s clock frequency to run true.
  • During the monitoring period described in ‘b’ the GPS is also outputting NMEA sentences that describe the time of the last 1pps and other stuff like geolocation. The time it outputs is based on the Almanac resident in it’s memory (see point ‘a’),  but KIWI-OSD ignores the NMEA sentences during this period.
  • At the end of the monitoring period, KIWI takes a look at the NMEA sentences and receives the first time data.  It outputs Geolocation data and outputs the first timestamp onto Field #00001.
  • KIWI-OSD then ignores the NMEA sentences thereafter, and ONLY increments the time display based on the sequence of 1pps signals.
  • Sometime during the next 12 minutes or so of uninterrupted running, it downloads a fresh Almanac from the satellite constellation and the GPS will output NMEA sentences with the correct time.  This maybe the same as the almanac that it used last night, or it will be different to the one installed in the factory in 2004.  KIWI-OSD will never know because it’s ignoring the NMEA sentences.
  • When the operator presses the reset button (and only then), KIWI-OSD takes a look at the NMEA sentence to get the time.

If it’s the same as the startup time + ‘x’ number of 1pps signals, then KIWI-OSD outputs a “PREVIOUS TMES OK” message.

If the time is different, then it outputs an “ERROR USE FIELD COUNT” message.

  • If you have received “ERROR USE FIELD COUNT “ message then you are good to go.  Simply press the reset button again to force a restart to observe your event(s).
  • If however you received an “PREVIOUS TMES OK” message then you are left guessing; Was the 12 minutes I allowed to download the fresh almanac enough? Was the 12 minutes uninterrupted – did it get ½ way through the download, and the GPS loose signal and have to start over? Remember KIWI-OSD doesn’t output the satellite count, so you’ll never know, until you press that reset button again, and again and again.  And again (twice) for good measure.  In all likelihood, it will be OK – but you’ll never know fore sure until you press that dam button.
  • Note:- If you do however get an unexpected “ERROR USE FIELD COUNT “ message, the only way you can indeed use the field counts to salvage your observation is if you have recorded the start up sequence and say 10 seconds of running.

IOTA-VTI on the other hand monitors the GPS every second, keeping watch on both the 1pps and the NMEA sentences and if there is an error in either it alerts the observer immediately, and reports exactly when the error occurred.